Resistance of Tuta absoluta to insecticides - … of Tuta absoluta to insecticides Because of the...

Resistance of Tuta absoluta to insecticides

Because of the short generation time and the frequent applications of insecticide to manage T. absoluta resistance to several insecticides has developed. In 1999 significant resistance of T. absoluta to acephate and deltamethrin was reported1. In the same year resistance to deltamethrin, lamba=cyhalothrin, mevinphos, metamidophos and esphenvalerate was reported in Chile2. In 2000 resistance to Cartap was reported in Brazil3,4. In 2001 resistance to abamectin was additionally reported in Brazil4,5. In 2005 an Argentine study confirmed T. absoluta resistance in that country to deltamethrin and abamectin as well as methamidophos6. Among the widely used insecticides that are still effective are imidacloprid7 and Bacillus thruingiensis.

References

1. CASTELO BRANCO, M.; FRANÇA, F.H., MEDEIROS, M.A.; LEAL, J.G.T. Uso de inseticidas para o controle da traça-do-tomateiro e traça-dascrucíferas: um estudo de caso. Horticultura Brasileira, v. 19 n. 1, p. 60-63, março, 2001.2. SALAZAR E.; ARAYA J. Tomato moth, Tuta absoluta (Meyrick) response to insecticides in Arica, Chile. Agric. Téc. v.61 n.4 Chillán oct. 20013. SIQUEIRA H. A. A. ,GUEDES R. N. C.; PICANCO M. C. Cartap resistance and synergism in populations of Tuta absoluta (Lep., Gelechiidae). J. Appl. Ent. 124, 233-238. 20004. SIQUEIRA H. A. A. ,GUEDES R. N. C.; PICANCO M. C . Insecticide resistance in populations of Tuta absoluta (Lepidoptera: Gelechiidae). Agricultural and Forest Entomology. Volume 2, Issue 2, Pages 147-153. 20015. SIQUEIRA H. A. A., GUEDES R. N. C, FRAGOSO D. B and MAGALHA L. C. Abamectin resistance and synergism in Brazilian populations of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) International Journal of Pest Management. 47(4) 247-251. 20016. LIETTII M., BOTTOII E., ALZOGARAY R. Insecticide resistance in Argentine populations of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). Neotrop. Entomol. vol.34 no.1 Londrina Jan./Feb. 20057. DANTE.M; GIMÉNEZ R. Efficacy of imidacloprid to control the tomato borer (Tuta absoluta meyrick). IDESIA (Chile) V 26, Nº 1, p 65-67. 2008

60 Hortic. bras., v. 19, n. 1, mar. 2001.

Em agosto de 1999, foi verificado queno Núcleo Rural da Taquara (DF) a

produção de tomate e brassicas estavaseriamente comprometida devido aosdanos ocasionados pela traça-do-toma-teiro (Tuta absoluta) e pela traça-das-crucíferas (Plutella xylostella). Diver-sos tipos de inseticidas, com freqüênciaque variava de semanal a diária, foramutilizados na região. A impossibilidadede controle das pragas foi atribuída, pe-los agricultores, à possível “falsificaçãodos produtos”. Não foi levantada a hi-pótese de que a ineficiência dos produ-tos poderia ser devida à resistência daspragas aos inseticidas. Resistência detraça-do-tomateiro a cartap já foi obser-vada no Brasil (Siqueira et al., 2.000) e

CASTELO BRANCO, M.; FRANÇA, F.H., MEDEIROS, M.A.; LEAL, J.G.T. Uso de inseticidas para o controle da traça-do-tomateiro e traça-das-crucíferas: um estudo de caso. Horticultura Brasileira, v. 19 n. 1, p. 60-63, março, 2.001.

Uso de inseticidas para o controle da traça-do-tomateiro e traça-das-crucíferas: um estudo de caso.Marina Castelo Branco1; Félix H. França1; Maria A. Medeiros1, José Guilherme T. Leal2

1/Embrapa Hortaliças, C. Postal 218, 70.359-970, Brasília - D.F; E-mail: [email protected] 2/EMATER-DF. Escritório LocalNúcleo Rural da Taquara, s/n. 70.000-000 Brasília – DF

RESUMOEm agosto de 1999, produtores de tomate e brassicas da Núcleo

Rural da Taquara tiveram seus cultivos seriamente comprometidosdevido à impossibilidade de controle da traça-do-tomateiro e da tra-ça-das-crucíferas. Diversos inseticidas, alguns com o mesmo prin-cípio ativo ou, pertencentes ao mesmo grupo químico, eram aplica-dos de uma a sete vezes por semana sem qualquer eficiência nocontrole das pragas. Lavouras foram abandonadas em diferentes estádiosde desenvolvimento. A fim de definir uma estratégia de controleque viabilizasse a produção de tomate e brassicas na região, foi ava-liado em laboratório a eficiência da dose comercial de alguns inseti-cidas usados no controle das duas pragas. Para isso, foram coletadasduas populações de traça-do-tomateiro e uma população de traça-das-crucíferas. Para traça-do-tomateiro, cartap, abamectin, lufenuron,acefate e deltametrina causaram respectivamente 100; 90; 67 e 0%de mortalidade das larvas. Para traça-das-crucíferas, B. thuringiensis,abamectin, cartap, acefate and deltametrina causaram 100; 96; 86;79 e 5% de mortalidade respectivamente. De acordo com estes re-sultados foi recomendada a suspensão imediata do uso de piretróidese organofosforados para o controle das duas pragas. Abamectin ecartap foram recomendados para o controle da traça-do-tomateiro eB. thuringiensis para o controle de traça-das-crucíferas.

Palavras-chave: Brassica oleracea, Lycopersicon esculentum,Tuta absoluta, Plutella xylostella, tomate, repolho, couve-flor,controle químico, resistência a inseticida.

ABSTRACTUse of insecticides for controlling the South American Tomato

Pinworm and the Diamondback Moth: a case study.

In August 1999, at the “Núcleo Rural da Taquara”, FederalDistrict, Brazil, tomato and brassica crops were severely damagedby the South American Tomato Pinworm (Tuta absoluta) and theDiamondback Moth (Plutella xylostella). During that time growersrelated that they had been spraying insecticides one to seven timesper week without controlling the pests. In the fields it was observedthat there were crops with different ages and levels of chemicalresidues which allowed the pests to multiplicate continuously. Thenit was decided that the first step to solve the problem would be toevaluate the efficacy of the recommended field rate of someinsecticides in laboratory bioassays. Two Brazilian Tomato Pinwormpopulations and one Diamondback Moth population were collected.Cartap, abamectin, lufenuron, acephate and deltamethrin caused 100;90; 67 and 0% of larval mortality to the South American TomatoPinworm, respectively. B. thuringiensis, abamectin, cartap, acephateand deltamethrin caused 100; 96; 86; 79 and 5% of mortality to theDiamondback Moth, respectively. According to laboratory results itwas recommended that the use of pyrethroid and organophosphorouscompounds must be suspended immediately. Abamectin and cartapmust be used to control the South American Tomato Pinworm andB. thuringiensis must be employed to Diamondback Moth control.

Keywords: Brassica oleracea, Lycopersicon esculentum, Tutaabsoluta, Plutella xylostella, tomato, cabbage, cauliflower,chemical control, insecticide resistance.

(Aceito para publicação em 04 de janeiro de 2.001).

resistência de traça-das-crucíferas a di-versos inseticidas já foi observada emvárias partes do mundo (Castelo Branco& Gatehouse, 1997; Cameron & Walker,1998; Baker, 1999; Kovaliski, 1999).

Observações preliminares de tomatedo local constataram a presença de mi-nas de traça-do-tomateiro em pratica-mente todas as folhas e, em alguns ca-sos, até 100% de frutos danificados. Emlavouras de brassicas foram observadosfuros de traça-das-crucíferas em folhasde repolho e couve-flor e, em um cultivode couve-flor, foram encontradas mais de100 larvas/planta. O sistema de produ-ção destas culturas envolvia: plantio con-tínuo e sucessivo de tomate e brassicas;abandono de restos culturais nas áreas de

cultivo; mistura de inseticidas; utilizaçãoem rotação de dois ou três produtos dife-rentes, em uma mesma semana, sem ob-servação de critérios técnicos.

Zhao et al. (1995), em ensaios reali-zados na China, observaram que testesde laboratório onde se avaliava a eficiên-cia da dose comercial de inseticidas parao controle da traça-das-crucíferas erambons indicadores da eficiência dos inse-ticidas em campo. A fim de determinarquais os inseticidas ineficientes para ocontrole da traça-das-crucíferas e traça-do-tomateiro no Núcleo Rural daTaquara, testes de laboratório foram rea-lizados. De posse destes dados e das ob-servações de campo, recomendações parao manejo da cultura foram sugeridas.

61Hortic. bras., v. 19, n. 1, mar. 2001.

MATERIAIS E MÉTODOS

1. Populações coletadasForam coletados ovos, larvas e

pupas de duas populações de traça-do-tomateiro (Populações 1 e 2) e de umapopulação de traça-das-crucíferas (Po-pulação 3) no Núcleo Rural da Taquara.Os agricultores forneceram dados sobreos inseticidas utilizados e freqüência deaplicação, conforme segue:

1.1 Traça-do-tomateiro: abamectin,Bacillus thuringiensis, chlorfluzuron,ciflutrina, deltametrina, fenpropatrina,lufenuron, metomil, permetrina etriflumuron. As pulverizações foramrealizadas com um inseticida ou commistura de produtos a cada 24 horas.

1.2 Traça-do-tomateiro: abamectin,Bacillus thuringiensis, betaciflutrina,ciflutrina, cartap, fenpropatrina,lufenuron, metomil, permetrina,triflumuron. As pulverizações eram rea-lizadas a cada três dias, com um inseti-cida ou com mistura de dois inseticidas(piretróide + lufenuron).

1.3 Traça-das-crucíferas: abamectin,chlorfluzuron, deltametrina, metamidofóse outros inseticidas não identificados. Aspulverizações eram feitas com interva-lo que variavam de um a três dias.

2. Bioensaios2.1. Traça-do-tomateiro: Foram

utilizadas larvas de segundo e terceiroestádio de traça-do-tomateiro provenien-tes diretamente do campo. Os insetici-das abamectin (9 g.i.a./ha), acefate (750g.i.a./ha), cartap (625 g.i.a./ha),deltametrina (10 g.i.a./ha) e lufenuron(40 g.i.a./ha) foram diluídos consideran-do-se o volume de calda de 1.000 L/ha.Folíolos que não continham larvas detraça-do-tomateiro foram imersos nasolução de inseticida por 10 segundose, em seguida, colocados para secar atemperatura ambiente. Após estaremsecos, 10-15 larvas de traça-do-tomatei-ro foram colocadas em três folíolos emplaca de Petri (15 cm de diâmetro). Emoutro teste, folíolos infestados com lar-vas de traça-do-tomateiro foram imersosna solução de inseticida por 10 segun-dos (10-15 larvas/repetição) e transfe-ridos para placas de Petri. Foram utili-zadas quatro repetições por tratamento.

Para todos os inseticidas, a mortali-dade de larvas foi avaliada após 24 h,exceto para lufenuron, onde a mortali-dade de larvas foi avaliada após seisdias. Para este último inseticida foi ain-da avaliado o número de adultos emer-gidos. Para a população 1 foram testa-dos abamectin, acefate, deltametrina elufenuron. Para a população 2 foram tes-tados acefate, cartap e deltametrina. Osprodutos cuja mortalidade de larvas foisuperior a 90% foram considerados comoeficientes para o controle da praga.

Para a análise estatística foi utiliza-do o esquema fatorial 5 x 2 e 4 x 2 [in-seticidas x posição das larvas nas folhas(sobre ou dentro das minas)] para aspopulações 1 e 2, respectivamente. Osdados foram submetidos à análise devariância e ao teste DMS (p<0,05) paraa separação das médias.

2.2.Traça-das-crucíferas: Larvas epupas foram coletadas em cultivo decouve-flor e criadas em laboratório atéa emergência de adultos. Os adultos fo-ram liberados em gaiola contendo fo-lhas de repolho para a obtenção dos ovosos quais foram mantidos em caixas plás-ticas com folhas de repolho até que aslarvas se desenvolvessem até o segun-do estádio, quando foram utilizadas nobioensaio. Foi avaliada a eficiência dosseguintes inseticidas: acefate (750 g i.a./ha), abamectin (9 g i.a./ha), Bacillusthuringiensis (18 g i.a./ha), cartap (300g i.a./ha) e deltametrina (6 gi.a./ha). Asdiluições foram realizadas consideran-do-se um volume de calda de 400 l/ha.

Discos de folhas de repolho de 4 cmde diâmetro foram imersos na soluçãoinseticida e secos à temperatura ambien-te, no laboratório. Foram transferidospara placas de Petri com 9 cm de diâ-metro e sobre cada folha foram coloca-das 15 larvas de traça-das-crucíferas.

A mortalidade de larvas foi avalia-da após 48 h. Os dados foram submeti-das à análise de variância e foi utilizadoo teste DMS (p<0,05) para a separaçãode médias.

2.3. Inimigos naturais: Um total de50 ovos de traça-do-tomateiro foramcoletados no campo em cada uma dasduas áreas de tomate. Os ovos foramindividualizados em cápsulas de gelati-na para a verificação de ocorrência deparasitóides.

Larvas de traça-das-crucíferascoletadas no campo foram também se-paradas e criadas até o estágio de pupa.Quando as pupas foram obtidas (172 nototal), foram individualizadas em cáp-sulas de gelatina para a observação daemergência de parasitóides ou adultosda praga.

RESULTADOS E DISCUSSÃO

1. Traça-do-tomateiro: Para as duaspopulações de traça-do-tomateiro hou-ve apenas efeito do inseticida na morta-lidade das larvas. Não houve efeito daposição das larvas sobre os folíolos (lar-vas sobre os folíolos ou no interior des-tes) nem da interação inseticida x posi-ção das larvas. Este resultado é diferen-te do observado por Castelo Branco &França (1993) onde, quando folhas detomate foram tratadas com cartap, amortalidade de larvas de traça-do-toma-teiro no interior das minas foi significa-tivamente menor do que a mortalidadede larvas sobre as folhas. A causa destadiferença não pôde ser identificada, masé possível que o grau de suscetibilidadedas populações ao inseticida de algumamaneira interfira nos resultados.

As doses comerciais dos inseticidasdeltametrina e acefate causaram a mor-talidade de menos de 2% das larvas daspopulações 1 e 2 (Tabelas 1 e 2).

Lufenuron ficou em uma posiçãointermediária, causando entre 67 e 72%de mortalidade das lagartas (Tabela 1).No entanto, este produto, por ser umregulador de crescimento, afeta tambéma emergência de adultos. Uma média de13% dos adultos emergiram, quando aslarvas foram colocadas sobre as folhas.Já quando as larvas estavam dentro dasfolhas, este percentual subiu para 26%.Ainda que mais de 10% dos adultos datraça-do-tomateiro tenham emergido,inseticidas reguladores de crescimentocomo lufenuron afetam a fertilidade defêmeas (França & Castelo Branco,1996), podendo contribuir para a redu-ção da população da praga em campo.

Abamectin causou a mortalidade demais de 90% das larvas da população 1(Tabela 1) e cartap causou a mortalida-de de todas as larvas da população 2(Tabela 2). Estes resultados indicam queestes dois inseticidas são os produtos

Uso de inseticidas para o controle da traça-do-tomateiro e traça-das-crucíferas: um estudo de caso.

62 Hortic. bras., v. 19, n. 1, mar. 2001.

mais eficientes para o controle da pragana região.

Dos 50 ovos da traça-do-tomateirocoletados de cada população, nenhumparasitóide emergiu. Este resultado podeindicar a ausência de parasitóides naregião ou a eliminação destes.

2. Traça-das-crucíferas:Deltametrina foi o produto menos eficien-te, causando a mortalidade de menos de6% das larvas (Tabela 3). Acefate ecartap se situaram em uma posição in-termediária com uma mortalidade varian-do de 79 a 86% (Tabela 3).Abamectin eBacillus thuringiensis causaram morta-

lidade superior a 96% (Tabela 3). Estesresultados indicaram uma boa eficáciados dois inseticidas para o controle dapraga. Abamectin não é registratdo paraa cultura de brássicas, não tendo por-tanto o seu uso recomendado.

Das 172 pupas de traça-das-crucíferas obtidas, apenas duas estavamparasitadas. Uma por Apanteles sp. e aoutra por Oomyzus sokolowiskii. Entreas pupas 87 originaram adultos e 83 nãoemergiram. Esta baixa ocorrência deparasitóides pode ser atribuída ao ele-vado número de aplicações de insetici-da e ao uso de produtos extremamente

tóxicos como por exemplo metamidofóse deltametrina (Talekar & Yang, 1991;Kao & Tzeng, 1992). Este resultado di-fere do observado por França &Medeiros (1998) onde em uma avalia-ção de inseticidas em campo foi obser-vada população alta de parasitóides (mé-dia > 4,0 adultos por planta) nas parce-las tratadas com deltametrina, indican-do a sobrevivência destes no local doexperimento. Como nesta área de culti-vo foram utilizados diferentes tipos deinseticida, não foi possível a identifica-ção dos produtos que mais contribuírampara a redução da população dos

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Tabela 1. Mortalidade de larvas de traça-do-tomateiro tratadas com diferentes inseticidas. Larvas sobre folhas ou no interior das minas.População 1. Taquara, Embrapa Hortaliças, 1999.

1/ número de larvas encontradas após 24 h para todos os inseticidas a exceção de Match®, onde o número de larvas é o número de larvasencontrado após seis dias.Médias seguidas de mesma letra não diferem entre si pelo teste DMS (p> 0,05)

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Tabela 2: Mortalidade de larvas de traça-do-tomateiro tratadas com diferentes inseticidas. Larvas sobre folhas ou no interior das minas.População 2. Taquara, Embrapa Hortaliças, 1999.

1/ número de larvas encontradas após 24 h para todos os inseticidas a exceção de Match®, onde o número de larvas é o número de larvasencontrado após seis dias.Médias seguidas de mesma letra não diferem entre si pelo teste DMS (p> 0,05)

M. Castelo Branco et al.

63Hortic. bras., v. 19, n. 1, mar. 2001.

parasitóides. Estudos que visem avaliara seletividade de alguns destes produ-tos se fazem necessários.

É sabido que as doses recomenda-das de qualquer inseticida são capazesde matar um determinado percentual dapopulação da praga, geralmente 95%,independentemente da sua densidadepopulacional (Knipling, 1979). Então,quando a densidade populacional é bai-xa, os produtos tendem a ser mais efi-cientes do que quando a densidadepopulacional é mais elevada. No NúcleoRural da Taquara, o sistema de produ-ção de tomate e brassicas (plantios su-cessivos e não eliminação de restos cul-turais) e as condições ambientais (tempoquente e seco) eram favoráveis ao cres-cimento descontrolado das populações detraça-das-crucíferas e traça-do-tomatei-ro (França et al., 1985; Haji et al., 1988;Castelo Branco, 1992). Deste modo, ne-nhum inseticida, mesmo os consideradoseficientes em testes de laboratório, apre-sentaram eficiência no campo.

Assim, para a viabilização de lavou-ras de tomate e brassicas na região esobrevivência de parasitóides e preda-dores que possam auxiliar na reduçãodas populações das pragas, são neces-sárias a implementação de medidas ra-cionais de uso de inseticidas e outraspráticas de manejo da cultura que visem,principalmente, reduzir as condiçõesfavoráveis ao crescimento populacionaldos insetos. São recomendadas as se-guintes medidas:

a) pulverizações semanais de inseti-cidas;

b) eliminação de inseticidas perten-centes a grupos químicos consideradosineficientes nos testes de laboratório;

c) introdução de um esquema de rota-ção de inseticidas (Castelo Branco, 2.000);

c) uso de irrigação por aspersão pararemoção de ovos e mortalidade de lar-vas e pupas (Costa et al., 1998;Junqueira et al., 1998);

d) destruição de restos culturais;e) não utilização de plantio

seqüenciado de tomate ou brássicas.As recomendações aqui descritas

foram seguidas por um agricultor doNúcleo Rural da Taquara e com isso foirecuperada uma lavoura de tomate e umplantio de couve-flor que já haviam sidoconsiderados perdidos.

AGRADECIMENTOS

A Hozanan P. Chaves pelo auxílionos trabalhos de campo e laboratório.Aos agricultores do Núcleo Rural daTaquara pelas informações prestadas.

LITERATURA CITADA

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CAMERON, P; WALKER, G. Warning: D.Bmoth resistant to pesticide. Commercial-Grower. v. 53, n. 2, p. 12-13, 1998.

CASTELO BRANCO, M. Flutuação populacionalda traça-do-tomateiro na região do DistritoFederal. Horticultura Brasileira, Brasília, v.10, p. 33-34, 1992.

CASTELO BRANCO, M. Como lidar com a re-sistência. Cultivar HF, v. 3, p. 25-27, 2000.

CASTELO BRANCO, M.; FRANÇA, F.H. Ava-liação da suscetibilidade de três populações deScrobipalpuloides absoluta a Cartap.Horticultura Brasileira, Brasília, v. 11, n. 1,p. 32-34, 1993.

CASTELO BRANCO, M.; GATEHOUSE, A.G.Insecticide resistance in Plutella xylostella(Lepidoptera: Yponomeutidae) in the FederalDistrict, Brazil. Anais da SociedadeEntomológica do Brasil, Jaboticabal, v. 26, p.75-79, 1997.

COSTA, J.S.; JUNQUEIRA, A.M.E.; SILVA,W.L.C.; FRANÇA, F.H. Impacto da irrigaçãovia pivô-central no controle da traça-do-toma-teiro. Horticultura Brasileira, Brasília, v. 16,n. 1, p. 19-23, 1998.

FRANÇA, F.H.; CASTELO BRANCO, M. Con-trole de pragas de hortaliças com produtos re-guladores de crescimento de insetos.Horticultura Brasileira, Brasília, v.14, n. 1, p.4-8, 1996.

FRANÇA, F.H.; MEDEIROS, M.A. Impacto dacombinação de inseticidas sobre a produçãode repolho e parasitóides associados com a tra-ça-das-crucíferas. Horticultura Brasileira,Brasília, v. 16, n. 2, p. 132-135, 1998.

FRANÇA, F.H.; CORDEIRO, C.M.T.;GIORDANO, L.B.; RESENDE, A.M. Contro-le da traça-das-crucíferas em repolho, 1984.Horticultura Brasileira, Brasília, v. 3, n. 2,p.47-53, 1985.

HAJI, F.N.P.; OLIVEIRA, C.A.V.; AMORIMNETO, M.S.; BATISTA, J.G.S. Flutuaçãopopulacional da traça-do-tomateiro noSubmédio São Francisco. PesquisaAgropecuária Brasileira, Brasília, v. 23, n. 1,p. 7-14, 1988.

JUNQUEIRA, A.M.R.; COSTA, J.S.; CASTELOBRANCO, M. FRANÇA, F.H. Impacto dediferentes lâminas de irrigação nos danos dePlutella xylostella em plantas de repolho. In:CONGRESSO BRASILEIRO DEOLERICULTURA, 38., 1998, Petrolina. Re-sumos... Petrolina, SOB, 1998. Resumo 140.

KAO, S.S.; TZENG, C.C. Toxicity of insecticidesto Cotesis plutellae, a parasitoid of theDiamondback Moth. In: TALEKAR, N.S.(Ed.). Diamondback Moth and other cruciferpests: Proceedings of the Second InternationalWorkshop. Taiwan: AVRDC, 1992. p. 287-296.

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SIQUEIRA, H.A.A.; GUEDES, R.N.C.;PICANÇO, M.; OLIVEIRA, E.E. Cartapresistance and synergism in populations of Tutaabsoluta (Lepidoptera: Gelechiidae). In.INTERNATIONAL CONGRESS OFENTOMOLOGY, 21; BRAZILIANCONGRESS OF ENTOMOLOGY, 18., 2000.Foz do Iguaçu, Abstracts. Londrina: SEB/Embrapa Soja, 2000. v. 1, p. 353.

TALEKAR, N.S.; YANG, J.C. Characteristic ofparasitism of diamondback moth by two larvalparasites. Entomophaga, v. 36, p. 95-104,1991.

ZHAO, J.Z.; WU, S.C.; ZHU, G.R. Bioassays withrecommended field concentrations of severalinsecticides for resistance monitoring inPlutella xylostella. Resistant PestManagement, v. 7, n. 1, p. 13-14,1995.

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Tabela 3 Mortalidade de larvas de traça-das-crucíferas tratadas com diferentes inseticidas.População 3. Taquara, Embrapa Hortaliças, 1999.

Médias seguidas de mesma letra não diferem entre si pelo teste DMS (p> 0,05)

Uso de inseticidas para o controle da traça-do-tomateiro e traça-das-crucíferas: um estudo de caso.

Agricultura Técnica

Agric. Téc. v.61 n.4 Chillán oct. 2001

RESPUESTA DE LA POLILLA DEL TOMATE, Tuta absoluta (Meyrick),

A INSECTICIDAS EN ARICA1

Tomato moth, Tuta absoluta (Meyrick) response to insecticides in Arica, Chile

Erika R. Salazar2 y Jaime E. Araya3

1 Recepción de originales: 22 de noviembre de 1999. 2 Instituto de Investigaciones Agropecuarias, Centro Regional de Investigación La Platina, Casilla 439, Correo 3, Santiago, Chile. 3 Universidad de Chile, Facultad de Ciencias Agronómicas, Departamento de Sanidad Vegetal, Casilla 1004, Santiago, Chile. E-mail: [email protected]

ABSTRACT

Larval susceptibility of Tuta absoluta (Meyrick) collected on tomato (Lycopersicon esculentun Mill.) crops in Azapa, Arica (18º 31 S lat, 70º 11 W long), Chile, was compared by toxicological tests with several commonly used insecticide doses applied on two development stage larvae groups (stadia 1-2 and 3-4). To determine resistance to insecticides, LD50, LD90, and regression slopes between probit mortality and log dosage were calculated. Resistance to studied insecticides was verified, since LD50 at least doubled those in Ovalle and Quillota, locations where T. absoluta had the greatest resistance in other study. Deltamethrin and mevinphos were the least and most toxic compounds, respectively. Larvae of both development levels were equally susceptible to deltamethrin, while larger larvae were more resistant to mevinphos than smaller ones. Results with esfenvalerate and - cyhalothrin on large larvae, and metamidophos on small larvae, were too variable and this caused a defective probit analysis and resistance evaluation to these insecticides in such larval groups. Parasite may have also developed resistance to insecticides; this may explain the resurgence of populations in the Valley. Possible parasite resistance, which are present even with insecticide treatments at extremely high dosages, could have affected accuracy in the regressions obtained, particularly on large larvae.

Key words: Deltamethrin, esfenvalerate, - cyhalothrin, mevinphos, metamidophos.

RESUMEN

Se comparó la susceptibilidad larvaria de la polilla del tomate, Tuta absoluta (Meyrick), colectada en tomate (Lycopersicon esculentun Mill.) en Azapa, Arica (18º 31 lat. Sur, 70º 11 long. Oeste), mediante pruebas de toxicología con varias dosis de insecticidas de uso común, aplicados sobre grupos de larvas de dos niveles de desarrollo (estadíos 1-2 y 3-4). Para determinar la resistencia a los insecticidas se

calcularon las DL50, DL90 y pendientes de las regresiones entre mortalidad (probit) y dosis (log). Se verificó la resistencia a los insecticidas estudiados, pues las DL50 al menos duplicaron aquellas en Ovalle y Quillota, localidades donde T. absoluta presentó la mayor resistencia en otro estudio. Deltametrina y mevinfos fueron los compuestos menos y más tóxicos, respectivamente. Las larvas de ambos niveles de desarrollo fueron igualmente susceptibles a deltametrina, mientras que las larvas grandes fueron más resistentes a mevinfos que las pequeñas. Los resultados con esfenvalerato y - cihalotrina sobre larvas grandes, y metamidofos en larvas pequeñas fueron muy variables, lo que impidió un buen ajuste probit y la evaluación de resistencia a estos compuestos en dichos grupos larvarios. El parásito también puede haber desarrollado resistencia a insecticidas, lo que puede explicar que en el Valle se hayan restablecido sus poblaciones. La posible resistencia de parásitos, presentes incluso en tratamientos insecticidas a dosis extremadamente altas, podría haber afectado la precisión de las regresiones obtenidas, especialmente sobre larvas grandes. Palabras clave: Deltametrina, esfenvalerato, - cihalotrina, mevinfos, metamidofos.

INTRODUCCIÓN

La polilla Tuta absoluta (=Scrobipalpuloides absoluta) (Meyrick) (Lepidoptera: Gelechiidae) es clave en el cultivo del tomate (Lycopersicon esculentum Mill.) en Chile (González, 1989; Prado, 1991); en cada temporada, el cultivo requiere aplicaciones frecuentes de insecticidas para evitar una reducción drástica de la producción y calidad de los frutos (Vargas, 1970; Apablaza, 1984). Salazar y Araya (1997) describieron la importancia de los daños y comprobaron el desarrollo de resistencia a algunos de estos compuestos mencionado por diversos autores (Acuña, 1970; Vargas, 1970; Campos, 1976; Moore, 1983) en varias localidades productoras.

Los insecticidas pueden aumentar los rendimientos al reducir los daños causados por las plagas, pero su uso repetido puede seleccionar gradualmente insectos resistentes (Lockwood et al., 1984; Brattsten, 1989; Metcalf, 1989).

Los cultivos de tomate en el Valle de Azapa reciben 15-17 aplicaciones de numerosos insecticidas en la temporada para controlar a T. absoluta, muchas veces en mezclas y con dosis mayores a las comerciales, lo que sugiere el desarrollo de resistencia. El objetivo de este estudio fue evaluar en laboratorio, con una metodología simple y de bajo costo, la efectividad de algunos insecticidas de uso habitual en el control de la polilla del tomate en el Valle de Azapa, utilizando larvas obtenidas en rastrojos de tomate.

MATERIALES Y MÉTODOS

Las pruebas se hicieron con larvas colectadas en rastrojos de tomate en el Valle de Azapa, en el Centro de Investigación y Capacitación Agrícola (CICA), San Miguel de Azapa (18º 31 lat Sur; 70º 11 long Oeste), Universidad de Tarapacá (a 12 km de Arica), en 1995. Se evaluaron los piretroides deltametrina (Decis 2,5 EC®), esfenvalerato (Halmark 7% LE®) y - cihalotrina (Karate 5% EC®), y los fosforados mevinfos (Phosdrin 24% LE®) y metamidofos [Monitor 600 (g L-1) CS®], por su amplia utilización por productores de tomate (Salazar y Araya, 1997).

Las larvas se colectaron del follaje de rastrojos de tomate con pincel y se utilizaron diariamente, manteniendo el excedente a baja temperatura (alrededor de 5ºC) para uso en pruebas posteriores. En cada tratamiento se usaron larvas pequeñas (estadíos 1-2, de 1,0-2,5 mm de longitud) y grandes (estadíos 3-4, de 4,5-7,5 mm). Las larvas de 2,5-4,5 mm se descartaron, para separar claramente ambos tamaños larvarios.

En las pruebas se determinó la mortalidad por contacto, asperjando con un aspersor manual De Vilbiss 1 mL de solución insecticida sobre grupos de 20 larvas seleccionadas al azar, en placas Petri inclinadas 45° de la horizontal, con papel filtro N°1 en el fondo. Aspersiones sobre papel fotográfico determinaron una gota similar a la de la torre Potter utilizada por Salazar y Araya (1997) y el aspersor manual a 1 m entre el aspersor y la placa Petri en este estudio. Se aplicaron al menos cinco dosis crecientes por insecticida y tamaño larvario, desde las dosis mínimas comerciales (0,4 mL L-1 de mezcla insecticida para los piretroides, y 1 ó 2 mL L-1 para los fosforados metamidofos y mevinfos, respectivamente), con tres repeticiones por tratamiento. Una vez secas, las larvas tratadas se trasladaron a frascos con follaje fresco de tomate sin insecticida y se mantuvieron a 18±2°C. La mortalidad se evaluó a las 48 h, considerando muertas aquellas larvas sin motilidad al ser estimuladas con pincel.

Para verificar la acción de cada insecticida (Busvine, 1980), los resultados de mortalidad se corrigieron por la fórmula de Abbott (1925) y procesaron mediante análisis probit (Finney, 1971; Busvine, 1980), siguiendo la metodología aplicada por Salazar y Araya (1997), para calcular, utilizando el programa computacional POLO PC, las DL50, DL90 y pendientes de las regresiones entre mortalidad (probit) y dosis (log). Se realizaron pruebas de Chi2 para comprobar el ajuste entre las mortalidades obtenidas y las esperadas, y corroborar el análisis probit. Las DL50 se analizaron mediante análisis de varianza; los promedios se separaron mediante pruebas de rango múltiple de Duncan (1955). Las diferencias estadísticas entre las pendientes de las regresiones se evaluaron mediante la prueba t de Student.

RESULTADOS Y DISCUSIÓN

Los resultados del análisis por insecticida se presentan en los Cuadros 1-3. Al no obtenerse mortalidad mayor al 90% con dosis razonables de insecticida, algunos DL90 se estimaron con las ecuaciones obtenidas con el programa POLO PC.

El Cuadro 1 presenta las DL50, intervalos de confianza al 95% y pendientes ± desviación estándar de la regresión lineal de los insecticidas evaluados.

Cuadro 1. Respuesta de larvas de Tuta. absoluta de San Miguel de Azapa, Arica1. Table 1. Tuta absoluta larvae response from San Miguel de Azapa, Arica1.

Insecticidas DL50 Intervalo de confianza al 95%

Pendiente ± desviación estándar

Estadíos 1-2

Deltametrina 571,26 201,30 - 412,09 2,72±0,31

Esfenvalerato 46,12 _ 1,18±0,25

- cihalotrina 35,28 17,40 - 332,94 0,96±0,16

Mevinfos 21,45 - 3,11±0,42

Estadíos 3-4

Deltametrina 476,09 _ 2,39±0,46

Mevinfos 35,84 26,02 - 53,76 23,29±0,35

Metamidofos 24,21 _ 1,94±0,29

1 Las poblaciones no presentaron distribución normal, lo que impidió su análisis estadístico.

Las pruebas de Chi2 indicaron que las rectas log (dosis) x mortalidad de esfenvalerato y - cihalotrina para larvas grandes (estadíos 1-2), y metamidofos para larvas pequeñas (estadíos 3-4), no se ajustaron a poblaciones de distribución normal de tolerancia, lo que impidió su análisis estadístico. Sin embargo, a pesar que la metodología en este ensayo es menos precisa que la que utiliza la torre Potter, igualmente se constató la poca eficiencia y la posible resistencia a los insecticidas estudiados, pues las DL50 obtenidas al menos duplican aquellas determinadas para Ovalle y Quillota, localidades con los mayores niveles de resistencia en el estudio de Salazar y Araya (1997).

Deltametrina no causó diferencias significativas de susceptibilidad entre ambos tamaños larvarios, aunque la mayor DL50 numérica ocurrió con las larvas pequeñas (Cuadro 2). Este resultado, diferente a los obtenidos por Salazar y Araya (1997) en otras localidades, pudo deberse al diferente método de aplicación de los insecticidas. En el tratamiento con mevinfos las larvas grandes fueron más resistentes que las pequeñas. Cuadro 2. DL50 (mL L-1) de los dos grupos larvarios (estadios 1-2 y 3-4) de Tuta absoluta de San Miguel de Azapa, Arica, tratados con cinco insecticidas1. Table 2. LD50 (mL L-1) of both larval groups (stadia 1-2 and 3-4) of Tuta absoluta from San Miguel de Azapa, Arica, treated with five insecticides1.

Larvas Estadíos 1-2 Estadíos 3-4 Deltametrina 571,26 a 447,09 a Esfenvalerato 46,12 -

- cihalotrina 35,27 -

Mevinfos 21,45 b 35,84 a Metamidofos - 24,21

1 Promedios en cada columna con letras iguales no son diferentes significativamente (P=0,05). El signo - indica que no hubo un buen ajuste probit.

Para las larvas de San Miguel de Azapa, deltametrina y mevinfos fueron los compuestos de menor y mayor toxicidad, respectivamente (Cuadro 3). Cuadro 3. Resistencia relativa de las larvas de Tuta absoluta de San Miguel de Azapa, Arica, a los insecticidas, en DL50 múltiplos de la dosis comercial1. Table 3. Tuta absoluta larvae from San Miguel de Azapa, Arica, relative resistance to the insecticides, in LD50-folds of the commercial dosage1.

Ingrediente activo Estadíos 1-2 Estadíos 3-4

Deltametrina 1428,16 a 1117,72a

Esfenvalerato 115,30 b -

- cihalotrina 88,19 b -

Mevinfos 17,92 c 10,72 c

Metamidofos - 24,21 b

1 Promedios en cada columna con letras iguales no son diferentes significativamente (P=0,05). El signo - indica que no hubo un buen ajuste probit. Salazar y Araya (1997) encontraron factores de resistencia (FR) a deltametrina de 7,1 y 8,2 para larvas grandes y pequeñas, respectivamente, de T. absoluta de Ovalle, y además confirmaron la resistencia a este piretroide en Quillota y Colina. También encontraron resistencia a esfenvalerato en Ovalle y Quillota, e incipiente en Colina, con FR de 2,0 y 1,9 para larvas grandes y pequeñas, respectivamente. Las mayores DL50 para - cihalotrina en larvas pequeñas y grandes ocurrieron en Ovalle y Quillota, respectivamente, con un menor nivel de resistencia en Colina. Sin embargo, estos autores indicaron que podrían haber subestimado los FR para deltametrina y esfenvalerato, debido a las altas dosis requeridas en ambos casos para matar al 50% de la población (control) susceptible de Requinoa, la que ya tendría algún grado de resistencia a estos insecticidas. Las poblaciones de Ovalle, Quillota y Colina fueron menos susceptibles a - cihalotrina. Las de Ovalle, Quillota y Colina fueron menos susceptibles para metamidofos que las de Requinoa. Para mevinfos, los mayores FR ocurrieron en Ovalle (5,45 y 4,72 para larvas grandes y pequeñas, respectivamente). Para todas las localidades, mevinfos fue el insecticida de mayor toxicidad relativa y por ende más efectivo. Sin embargo, el uso de este insecticida fue prohibido en Chile en 1995 por el Servicio Agrícola y Ganadero. En todas las localidades evaluadas por Salazar y Araya (1997), las larvas 3-4 fueron menos susceptibles a los insecticidas estudiados, en general con DL50 1,2-2,5 veces mayores que para larvas de menor desarrollo (estadíos 1-2). Estos resultados confirman otros informados en la literatura, pues la susceptibilidad a un producto químico disminuye con el aumento del tamaño larvario (Busvine, 1980).

En la comparación de Salazar y Araya (1997) de la toxicidad relativa de los insecticidas evaluados, mevinfos y deltametrina fueron los compuestos más y menos tóxicos, respectivamente, sobre todas las poblaciones de T. absoluta. De los piretroides evaluados para todas las localidades y tamaños larvarios, - cihalotrina

fue el más tóxico. En Ovalle, mevinfos y - cihalotrina fueron el fosforado y el piretroide más tóxicos. Metamidofos fue más tóxico que - cihalotrina sobre larvas grandes, mientras que ambos insecticidas no se diferenciaron estadísticamente en larvas pequeñas. En Quillota, mevinfos y - cihalotrina fueron los insecticidas más tóxicos. Los fosforados fueron más tóxicos que los piretroides en larvas grandes, mientras que mevinfos fue más tóxico que - cihalotrina sobre larvas pequeñas. Metamidofos fue el tercer insecticida en toxicidad. En Colina, mevinfos y - cihalotrina fueron también los insecticidas más tóxicos; se observó además, un aumento en la toxicidad de esfenvalerato sobre los resultados para Quillota y Ovalle, aunque sin diferencia estadística con metamidofos. En Requinoa, al igual que en las otras localidades, mevinfos y - cihalotrina fueron los compuestos más tóxicos. Ambos insecticidas presentaron resultados similares, con DL50 cercanos a las dosis comerciales recomendadas. Destacaron además, las DL50 para deltametrina sobre los estadíos 3-4 (29,85 veces) y 1-2 (12,34 veces), lo que evidenció una alta resistencia para deltametrina en esta localidad.

Si los resultados se comparan con los de Salazar y Araya (1997), se puede concluir que la población de Azapa ha desarrollado alta resistencia a los insecticidas estudiados. Esta hipótesis debe ser comprobada, sin embargo, utilizando una metodología de precisión similar a la de ese estudio, e incluyendo una población control susceptible.

Durante la evaluación de mortalidad se observaron algunas larvas grandes con alguna motilidad al estimulo con pincel, pero con tegumento marrón oscuro, por lo que se consideraron muertas. En otros recuentos se encontraron pupas de parásitos adosadas al cuerpo de las larvas de T. absoluta, revelando que aquellas larvas oscuras consideradas muertas estaban parasitadas. Se criaron algunas pupas, las que sin embargo se deshidrataron y no produjeron parasitoides adultos para su identificación. El parásito también puede haber desarrollado resistencia a insecticidas, lo que ha permitido que en el Valle de Azapa se restablezcan sus poblaciones (Vargas, 1970). La posible resistencia de parásitos larvarios es lógica al encontrarse larvas y/o pupas en sectores tratados con insecticidas en concentraciones extremadamente altas. Este factor podría haber afectado la precisión de las regresiones en los tratamientos sobre larvas grandes.

Una forma razonable de manejar la resistencia a los plaguicidas son programas de manejo integrado que reduzcan la frecuencia e intensidad de la selección y apliquen un mejor control natural y cultural, y el uso de variedades resistentes. En conjunto, estas medidas pueden eliminar gran parte de los individuos seleccionados antes que produzcan una progenie resistente a insecticidas (Metcalf, 1980). Para el manejo integrado es vital disminuir la presión de selección, aplicar insecticidas con menor frecuencia, evitar el uso de compuestos persistentes en el ambiente, formulaciones de lenta liberación, compuestos con presión de selección en varios estados de desarrollo del insecto, e incorporar métodos alternativos biológicos y culturales (Metcalf, 1980, 1989). Para manejar los insecticidas se deben analizar las poblaciones para conocer la susceptibilidad original y detectar temprano el desarrollo de resistencia, de manera de extender la vida útil de un insecticida hasta que la respuesta de la población indique la necesidad de cambiarlo. La secuencia de insecticidas alternativos debe limitar los compuestos con resistencia simple y cruzada (e.g., dimetoato y piretroides) y el uso de mezclas insecticidas. Se debe considerar el umbral económico, utilizar métodos

adecuados y aplicación oportuna, usar plaguicidas inocuos para los enemigos naturales, y productos selectivos en vez de compuestos tóxicos de amplio espectro.

Aunque la metodología en este trabajo logró resultados muy variables y fue menos precisa que la utilizada por Salazar y Araya (1997) con una torre Potter en laboratorio, nuestros resultados comprobaron la ineficacia de los insecticidas más utilizados contra T. absoluta en el Valle de Azapa, verificando el deterioro ambiental y productivo causado por la intervención con insecticidas de amplio espectro en ambientes poco diversificados y ecológicamente inestables. Se debe estudiar la incorporación de nuevos compuestos insecticidas con diversos modos de acción, de manera de evitar el desarrollo de resistencia y/o regenerar el sistema productivo de tomates en el extremo norte de Chile, con el objeto de proteger esta importante actividad agrícola, fuente de ingresos para numerosos productores durante todo el año, y evitar repetir situaciones de crisis productivas de tipo regional como las descritas por Metcalf (1989).

CONCLUSIONES

Aunque la metodología utilizada permitió una medición rápida de la pérdida de efectividad de los insecticidas más utilizados contra la polilla del tomate en el Valle de Azapa, algunos resultados fueron muy variables, lo que impidió un buen ajuste probit y la evaluación consiguiente de resistencia a estos compuestos. Estos estudios pueden afinarse mediante el uso de una torre de precisión tipo Potter y la comparación con una población susceptible. También se debe estudiar el desarrollo de resistencia a insecticidas en los enemigos naturales de T. absoluta, con miras a su posible utilización en programas de control integrado de esta plaga.

AGRADECIMIENTOS

Los autores agradecen la valiosa colaboración del Ingeniero Agrónomo Sr. Juan Machuca del Servicio Agrícola y Ganadero, Arica, y de los entomólogos Sres. Héctor Vargas y Dante Bobadilla, CICA, San Miguel de Azapa, Universidad de Tarapacá.

LITERATURA CITADA

Abbott, W.S. 1925. A method for computing the effectiveness of an insecticide. J. Econ. Entomol. 18:265-267. [ Links ]

Acuña, J. 1970. Control químico de la polilla del tomate Gnorimoschema absoluta (Meyr.). IDESIA, Universidad del Norte (Chile) 1:75-110. [ Links ]

Apablaza, J. 1984. Incidencia de insectos y moluscos plagas en siete hortalizas cultivadas en las regiones V y Metropolitana, Chile. Ciencia e Investigación Agraria 11:27-34. [ Links ]

Brattsten, L.B. 1989. Insecticide resistance: Research and management. Pestic. Sci. 26: 329-332. [ Links ]

Busvine, J.R. 1980. Recommended methods for measurement of pest resistance to pesticides. 132 p. FAO, Rome, Italy. [ Links ]

Campos, R. 1976. Control químico del "Minador de las hojas y tallos de la papa" (Scrobipalpula absoluta M.) en el Valle de Cañete. Rev. Peruana Entomol. 19:102-106. [ Links ]

Duncan, D.B. 1955. Multiple range and multiple F tests. Biometrics 11:1-42. [ Links ]

Finney, D.J. 1971. Probit analysis. 33 p. 3º ed. Cambridge Univ. Press, London, England. [ Links ]

Gonzalez, R.H. 1989. Insectos y ácaros de importancia agrícola y cuarentenaria en Chile. 310 p. Ograma, Santiago, Chile. [ Links ]

Lockwood, J.A., T.C. Sparks, and R.N. Story. 1984. Evolution of insect resistance to insecticide: A reevaluation of the roles of physiology and behavior. Bull. Entomol. Soc. Amer. 30:41-51. [ Links ]

Metcalf, R.L. 1980. Changing role of insecticides in crop protection. Ann. Rev. Entomol. 25:219-256. [ Links ]

Metcalf, R.L. 1989. Insect resistance to insecticides. Pestic. Sci. 26:333-358. [ Links ]

Moore, J. 1983. Control of tomato leafminer (S. absoluta) in Bolivia. Trop. Pest Management 29:231-238. [ Links ]

Prado, E. 1991. Artrópodos y sus enemigos naturales asociados a plantas cultivadas en Chile. 207 p. Serie Bol. Técnico Nº 169. Instituto de Investigaciones Agropecuarias, Santiago, Chile. [ Links ]

Salazar, E., y J.E. Araya. 1997. Detección de resistencia a insecticidas en la polilla del tomate. Simiente 67:8-22. [ Links ]

Vargas, H. 1970. Observaciones sobre la biología y enemigos naturales de la polilla del tomate. IDESIA, Universidad del Norte (Chile) 1:75-110. [ Links ]

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Agricultural and Forest EntomologyWhat is RSS?

Volume 2, Issue 2, Pages 147-153Published Online: 24 Dec 2001

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Insecticide resistance in populations of Tuta absoluta (Lepidoptera: Gelechiidae)

Herbert Álvaro A. Siqueira, Raul Narciso C. Guedes and Marcelo C. PicançoDepartamento de Biologia Animal, Universidade Federal de Viçosa, Viçosa, MG 36571 000, Brazil

Correspondence: Raul Narciso C. Guedes. Tel: + 55 31 899 2006; fax: + 55 31 899 2537; e-mail: [email protected]

KEYWORDSAbamectin • cartap • methamidophos • permethrin • tomato leafminer

ABSTRACT

Abstract1 Control failures of insecticides used against the tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in Brazilled to the investigation of the possible occurrence of resistance of this insect pest to abamectin, cartap, methamidophos andpermethrin.

2 The insect populations were collected from seven sites in the states of Minas Gerais, Rio de Janeiro, and São Paulo. Thesepopulations were subjected to concentration–mortality bioassays using insecticide-impregnated filter papers.

3 We were unable to obtain a single population which provided a susceptibility standard for all insecticides tested. Therefore,the resistance levels were estimated in relation to the most susceptible population to each insecticide. Resistance to abamectinand cartap were observed in all populations when compared with the susceptible standard population, with resistance ratiosranging from 5.2- to 9.4-fold and from 2.2- to 21.9-fold for abamectin and cartap, respectively. Resistance to permethrin wasobserved in five populations with resistance ratios ranging from 1.9- to 6.6-fold, whereas resistance to methamidophos wasobserved in four populations with resistance ratios ranging from 2.6- to 4.2-fold.

4 The long period and high frequency of use of these insecticides against this insect pest suggest that the evolution ofinsecticide resistance on them has been relatively slow. Alternatively, the phenomenon might be widespread among Brazilianpopulations of T. absoluta making the finding of suitable standard susceptible populations difficult and leading to anunderestimation of the insecticide resistance levels in this pest.

5 Higher levels of resistance to abamectin, cartap and permethrin are correlated with greater use of these compounds bygrowers. This finding suggests that local variation in insecticide use was an important cause of variation in susceptibility.

Accepted: 14 April 2000;

DIGITAL OBJECT IDENTIFIER (DOI)

10.1046/j.1461-9563.2000.00062.x About DOI

Introduction

The tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is an oligophagous insect which attacks solanaceouscrops, especially tomato, where it is one of its main pests ( Picanço et al. 1998 ). This insect was originally described in Peru,but it is widespread throughout South America ( Povolny 1975; Carballo et al. 1981 ; Muszinski et al. 1982 ; Souza & Reis

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< Previous Article

Agricultural and Forest EntomologyWhat is RSS?

Volume 2, Issue 2, Pages 147-153Published Online: 24 Dec 2001

All Content

Publication Titles

Advanced SearchCrossRef / Google SearchAcronym Finder

Save Article to My Profile Download CitationAbstract | References | Full Text: HTML

View with Table of Contents

Insecticide resistance in populations of Tuta absoluta (Lepidoptera: Gelechiidae)

Herbert Álvaro A. Siqueira, Raul Narciso C. Guedes and Marcelo C. PicançoDepartamento de Biologia Animal, Universidade Federal de Viçosa, Viçosa, MG 36571 000, Brazil

Correspondence: Raul Narciso C. Guedes. Tel: + 55 31 899 2006; fax: + 55 31 899 2537; e-mail: [email protected]

KEYWORDSAbamectin • cartap • methamidophos • permethrin • tomato leafminer

ABSTRACT

Abstract1 Control failures of insecticides used against the tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in Brazilled to the investigation of the possible occurrence of resistance of this insect pest to abamectin, cartap, methamidophos andpermethrin.

2 The insect populations were collected from seven sites in the states of Minas Gerais, Rio de Janeiro, and São Paulo. Thesepopulations were subjected to concentration–mortality bioassays using insecticide-impregnated filter papers.

3 We were unable to obtain a single population which provided a susceptibility standard for all insecticides tested. Therefore,the resistance levels were estimated in relation to the most susceptible population to each insecticide. Resistance to abamectinand cartap were observed in all populations when compared with the susceptible standard population, with resistance ratiosranging from 5.2- to 9.4-fold and from 2.2- to 21.9-fold for abamectin and cartap, respectively. Resistance to permethrin wasobserved in five populations with resistance ratios ranging from 1.9- to 6.6-fold, whereas resistance to methamidophos wasobserved in four populations with resistance ratios ranging from 2.6- to 4.2-fold.

4 The long period and high frequency of use of these insecticides against this insect pest suggest that the evolution ofinsecticide resistance on them has been relatively slow. Alternatively, the phenomenon might be widespread among Brazilianpopulations of T. absoluta making the finding of suitable standard susceptible populations difficult and leading to anunderestimation of the insecticide resistance levels in this pest.

5 Higher levels of resistance to abamectin, cartap and permethrin are correlated with greater use of these compounds bygrowers. This finding suggests that local variation in insecticide use was an important cause of variation in susceptibility.

Accepted: 14 April 2000;

DIGITAL OBJECT IDENTIFIER (DOI)

10.1046/j.1461-9563.2000.00062.x About DOI

Introduction

The tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is an oligophagous insect which attacks solanaceouscrops, especially tomato, where it is one of its main pests ( Picanço et al. 1998 ). This insect was originally described in Peru,but it is widespread throughout South America ( Povolny 1975; Carballo et al. 1981 ; Muszinski et al. 1982 ; Souza & Reis


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1986). It was initially reported in Brazil between September 1979 and October 1980 at Morretes county, state of Paraná, fromwhere it spread throughout the country, and has been considered a serious problem for tomato production since then (Muszinski et al. 1982 ; Souza & Reis 1986; França 1993; Guedes et al. 1994 ; Picanço et al. 1995 ).

The larval injury to the tomato plant leads to direct yield loss. The leafminers attack the tomato plants in all of theirdevelopmental stages, damaging the stems, apices, flowers and fruits besides mining their leaves ( Souza et al. 1992 ; Mirandaet al. 1998 ). This kind of damage resembles those of other Gelechiidae pests of solanaceous crops, such as Keiferialycopersicella (Wals.) in Central and North America and Phthorimaea operculella (Zell.) in the Americas, Europe, Africa andAsia ( Sannino & Nicodemo 1979; Juvick et al. 1982 ; Abbas et al. 1993 ; Ebora et al. 1994 ; Pouey et al. 1994 ). When in highdensities, T. absoluta is able to cause significant production losses in tomato crops ( Souza et al. 1992 ; Picanço et al. 1998 ).

The main control method for T. absoluta is the use of insecticides, but some of the compounds recommended for its control areapparently not providing the desired effect ( Castelo Branco & França 1992; Guedes et al. 1994 ). It has been hypothesized thatexcessive insecticide applications commonly applied to the tomato crop during a single cultivation period, sometimes up to 36sprays, could have led to the evolution of resistant populations, besides eliminating their natural enemies, and leading toadditional occupational hazards ( Castelo Branco & França 1992; Gonçalves et al. 1994 ; Picanço et al. 1995 ).

Permethrin and cartap were initially the only insecticides for use against T. absoluta, leading to their large scale utilization inBrazil for a long period ( Souza & Reis 1986). The use of abamectin and methamidophos is more recent (i.e. early 1990s) andabamectin, in mixture with mineral oil, shows high efficiency against the pest ( Guedes et al. 1995 ; Castelo Branco et al. 1996 ;Picanço et al. 1998 ). However, some investigators pointed out that the use of mineral oil in insecticide mixtures can increaseproblems of insecticide resistance in insect pest populations ( Castelo Branco et al. 1996 ; Picanço et al. 1996 ).

Insecticide resistance has been reported all over the world to almost every group of insecticides used against insect pests (Lockwood et al. 1984 ; Georghiou 1986; Kay & Collins 1987). Therefore, it is necessary to develop management tactics to delayor even prevent the evolution of insecticide resistance in insect pest populations, and the detection and monitoring of suchphenomena is of key importance to achieve this ( Dennehy et al. 1983 ; Tabashnik & Roush 1990). Owing to control failures ofinsecticides used against T. absoluta and the report of resistant populations of this pest in Chile ( Moore 1983; Salazar & Araya1997), the present study was carried out to detect the existence of Brazilian populations of T. absoluta resistant to the maininsecticides used against it and to quantify that resistance and its relationship with insecticide use in seven sites in Brazil.

Materials and methods

Five populations of T. absoluta from the state of Minas Gerais, one population from the state of Rio de Janeiro, and anotherfrom São Paulo ( Fig. 1; Table 1) were used in this study. These last two populations were obtained from laboratory colonies,established from local populations, with intended use as potential standard susceptible populations. For each of these sites,information on insecticide use was obtained from appropriate growers or State extension personnel. Colonies of T. absolutawere established from at least 200 larvae obtained from heavily infested leaves from each sampling site. The individualpopulations were reared on tomato plants of variety Santa Clara, without insecticide exposure, enclosed in cages andmaintained in a greenhouse.

Fig. 1 Sites of origin of the populations of tomato leafminer (T.absoluta) in the Brazilian states of Minas Gerais, Rio de Janeiro andSão Paulo. The numbers correspond to locations indicated inTable 1.[Normal View ]

Table 1 Origin and year of collection of populations of the tomato leafminer (T. absoluta).

Code number County State Place Month and year collected

1 Araguari Minas Gerais Field August 19982 Guiricema Minas Gerais Field September 19983 Lavras Minas Gerais Field August 19984 Uberlândia Minas Gerais Field April 19985 Viçosa Minas Gerais Field October 19976 São João da Barra Rio de Janeiro Laboratory August 19977 Paulínia São Paulo Laboratory August 1998

The four technical grade insecticides used were abamectin (Novartis Biociências, São Paulo, SP), cartap (Iharabrás, Sorocaba,SP), methamidophos (Bayer, São Paulo, SP), and permethrin (Zeneca Agrícola, Holambra, SP). All of these insecticides arecurrently recommended for controlling T. absoluta in Brazil.


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Insecticide bioassays were carried out using insecticide-impregnated filter paper (9 cm diameter) placed in Petri dishes (9 cmdiameter × 1.5 cm height). For each bioassay, six to seven different insecticide concentrations were applied; control treatments(acetone for abamectin and permethrin, ethanol for methamidophos, and distilled water for cartap) were included. Threereplicates with 20 second instar larvae of T. absoluta were used at each insecticide concentration. For each replicate, we useda filter paper impregnated with 1 mL of insecticide dissolved in the appropriate solvent (i.e. acetone, ethanol or distilled water).Insecticide concentrations were calculated as µg a.i./cm2 of treated surface. Insects were counted as dead if they were unableto walk. Concentration–mortality data were subjected to probit analysis (Proc Probit, Sas Institute 1997).

Correlation analysis (Proc CORR, Sas Institute 1997) was used to test the association between the insecticide use and itsresistance ratio across the sites studied. No association between insecticide use and resistance ratio could result from poorestimation of insecticide use, resistance ratio, or both, or lack of a causal relationship between insecticide use and resistanceratio. In addition, multiple regression analysis (Proc REG, Sas Institute 1997) was used to determine whether the use of theother insecticides contributed to variation in resistance ratio of a particular insecticide. The dependent variable (i.e. theresistance ratio of a particular insecticide) was used in the multiple regression models to test the four independent variables (i.e.the use of each of the four insecticides under investigation).

Results

The results of 2 test ( 2 and P values) used to measure how well the data of each concentration–response curve fit theassumptions of the probit model are presented on Tables 2–5. As values (responses) predicted by the probit model did not differsignificantly from values actually observed in the bioassays (low 2-values and P > 0.05), the probit model was suitable for theconcentration–response analyses.

Table 2 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to permethrin.

Population n Slope ± SEMLC50 (95% CL)µg a.i./cm2

LC90 (95% CL)µg a.i./cm2

Resistanceratio * 2 Prob.

Uberlândia 421 0.51 ± 0.04 47.8 (39.2–59.0) 319 (221–532) – 4.06 0.54Viçosa 362 0.63 ± 0.07 71.5 (58.7–85.9) 389 (275–669) 1.50 6.37 0.17Paulínia 360 0.70 ± 0.07 89.3 (76.6–103) 305 (237–447) 1.87 0.26 0.99Lavras 422 0.56 ± 0.09 142 (108–219) 575 (325–2194) 2.97 9.57 0.09São João da Barra 360 0.58 ± 0.08 158 (117–290) 528 (289–4475) 3.31 7.80 0.10Araguari 420 0.80 ± 0.07 187 (165–212) 600 (469–875) 3.90 5.63 0.34Guiricema 365 0.86 ± 0.07 316 (273–361) 1088 (845–1628) 6.61 2.59 0.63

* LC 50 resistant/LC50 susceptible.

Table 3 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to abamectin.




Uberlândia 360 0.80 ± 0.10 0.97 (0.87–1.09) 2.40 (1.99–3.14) – 4.34 0.36Paulínia 361 0.76 ± 0.12 5.00 (4.21–5.81) 18.2 (14.5–25.1) 5.16 3.30 0.51Guiricema 360 0.67 ± 0.06 5.87 (4.90–6.96) 21.9 (16.8–32.3) 6.04 2.80 0.59São João da Barra 420 0.45 ± 0.03 5.96 (4.51–7.52) 48.7 (35.1–76.7) 6.14 1.19 0.95Viçosa 421 0.49 ± 0.04 6.76 (5.28–8.37) 47.1 (34.8–71.2) 6.97 1.93 0.86Lavras 360 0.67 ± 0.08 8.31 (7.10–9.87) 34.7 (25.1–56.6) 8.57 0.48 0.98Araguari 360 0.63 ± 0.09 9.09 (7.68–10.92) 36.0 (25.3–65.0) 9.37 6.79 0.15


Table 4 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to methamidophos.


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Insecticide bioassays were carried out using insecticide-impregnated filter paper (9 cm diameter) placed in Petri dishes (9 cmdiameter × 1.5 cm height). For each bioassay, six to seven different insecticide concentrations were applied; control treatments(acetone for abamectin and permethrin, ethanol for methamidophos, and distilled water for cartap) were included. Threereplicates with 20 second instar larvae of T. absoluta were used at each insecticide concentration. For each replicate, we useda filter paper impregnated with 1 mL of insecticide dissolved in the appropriate solvent (i.e. acetone, ethanol or distilled water).Insecticide concentrations were calculated as µg a.i./cm2 of treated surface. Insects were counted as dead if they were unableto walk. Concentration–mortality data were subjected to probit analysis (Proc Probit, Sas Institute 1997).

Correlation analysis (Proc CORR, Sas Institute 1997) was used to test the association between the insecticide use and itsresistance ratio across the sites studied. No association between insecticide use and resistance ratio could result from poorestimation of insecticide use, resistance ratio, or both, or lack of a causal relationship between insecticide use and resistanceratio. In addition, multiple regression analysis (Proc REG, Sas Institute 1997) was used to determine whether the use of theother insecticides contributed to variation in resistance ratio of a particular insecticide. The dependent variable (i.e. theresistance ratio of a particular insecticide) was used in the multiple regression models to test the four independent variables (i.e.the use of each of the four insecticides under investigation).

Results

The results of 2 test ( 2 and P values) used to measure how well the data of each concentration–response curve fit theassumptions of the probit model are presented on Tables 2–5. As values (responses) predicted by the probit model did not differsignificantly from values actually observed in the bioassays (low 2-values and P > 0.05), the probit model was suitable for theconcentration–response analyses.

Table 2 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to permethrin.




Uberlândia 421 0.51 ± 0.04 47.8 (39.2–59.0) 319 (221–532) – 4.06 0.54Viçosa 362 0.63 ± 0.07 71.5 (58.7–85.9) 389 (275–669) 1.50 6.37 0.17Paulínia 360 0.70 ± 0.07 89.3 (76.6–103) 305 (237–447) 1.87 0.26 0.99Lavras 422 0.56 ± 0.09 142 (108–219) 575 (325–2194) 2.97 9.57 0.09São João da Barra 360 0.58 ± 0.08 158 (117–290) 528 (289–4475) 3.31 7.80 0.10Araguari 420 0.80 ± 0.07 187 (165–212) 600 (469–875) 3.90 5.63 0.34Guiricema 365 0.86 ± 0.07 316 (273–361) 1088 (845–1628) 6.61 2.59 0.63


Table 3 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to abamectin.




Uberlândia 360 0.80 ± 0.10 0.97 (0.87–1.09) 2.40 (1.99–3.14) – 4.34 0.36Paulínia 361 0.76 ± 0.12 5.00 (4.21–5.81) 18.2 (14.5–25.1) 5.16 3.30 0.51Guiricema 360 0.67 ± 0.06 5.87 (4.90–6.96) 21.9 (16.8–32.3) 6.04 2.80 0.59São João da Barra 420 0.45 ± 0.03 5.96 (4.51–7.52) 48.7 (35.1–76.7) 6.14 1.19 0.95Viçosa 421 0.49 ± 0.04 6.76 (5.28–8.37) 47.1 (34.8–71.2) 6.97 1.93 0.86Lavras 360 0.67 ± 0.08 8.31 (7.10–9.87) 34.7 (25.1–56.6) 8.57 0.48 0.98Araguari 360 0.63 ± 0.09 9.09 (7.68–10.92) 36.0 (25.3–65.0) 9.37 6.79 0.15


Table 4 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to methamidophos.


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São João da Barra 362 0.67 ± 0.06 59.9 (50.9–70.8) 243 (184–357) – 7.75 0.10Viçosa 401 0.62 ± 0.07 62.3 (53.9–72.1) 192 (154–256) 1.04 8.06 0.15Lavras 420 0.67 ± 0.05 79.3 (53.4–99.0) 239.6 (204–305) 1.32 7.78 0.17Uberlândia 440 0.80 ± 0.11 155 (137–175) 530 (420–744) 2.59 8.10 0.23Araguari 343 2.17 ± 0.42 191 (179–201) 279 (263–303) 3.19 5.34 0.25Paulínia 400 1.16 ± 0.17 225 (202–246) 473 (421–556) 3.76 5.66 0.34Guiricema 400 1.23 ± 0.16 252 (228–275) 535 (473–637) 4.22 7.51 0.19


Table 5 Comparative susceptibility of populations of tomato leafminer (T. absoluta) to cartap.




Paulínia 363 1.90 ± 0.21 0.44 (0.41–0.47) 0.74 (0.67–0.84) – 5.34 0.25Guiricema 363 2.24 ± 0.52 0.97 (0.92–1.03) 1.60 (1.39–2.19) 2.25 4.68 0.32Lavras 420 1.90 ± 0.20 1.87 (1.76–1.98) 3.15 (2.89–3.55) 4.22 5.06 0.41Uberlândia 400 1.04 ± 0.13 4.57 (4.13–5.04) 10.4 (9.08–12.5) 10.4 4.30 0.51Viçosa 420 0.71 ± 0.10 4.81 (4.22–5.47) 15.5 (12.5–20.7) 10.9 5.44 0.36São João da Barra 420 0.77 ± 0.04 7.16 (6.34–8.18) 20.9 (16.8–28.1) 16.2 6.66 0.25Araguari 341 1.01 ± 0.11 9.68 (8.47–10.87) 25.3 (21.3–32.4) 21.9 6.86 0.14


There was significant variation in the susceptibility among the insect populations studied for the four insecticides investigatedbased on the criterion of failure of 95% CL at the LC50s to overlap. We were unable to identify a general standard susceptiblepopulation. Therefore, the resistance ratios were taken by comparison with the population most susceptible to each insecticide.The population from Uberlândia was the most susceptible one for permethrin and abamectin ( Tables 2 and 3), whereas SãoJoão da Barra was the most susceptible to methamidophos ( Table 4) and Paulínia was most susceptible to cartap ( Table 5).

LC50s for permethrin were significantly greater for five of the populations of T. absoluta relative to the population fromUberlândia ( Table 2). LC50 for the population from Viçosa resembled that of Uberlândia and Paulínia, differing from theremaining ones. Permethrin resistance ratios ranged from 1.5- to 6.6-fold among the populations of the leafminer studied. LC50sfor abamectin were significantly greater for all insect populations when compared with the population from Uberlândia, withresistance ratios ranging from 5.2- to 9.4-fold ( Table 3).

Resistance to methamidophos was observed in only four insect populations when compared with the population from São Joãoda Barra, the most susceptible one to this insecticide ( Table 4). These four populations were from Araguari, Guiricema,Paulínia and Uberlândia, and their resistance ratios to methamidophos ranged from 2.6- to 4.2-fold. By contrast, the populationsfrom Lavras and Viçosa were susceptible to this insecticide. Resistance to cartap was observed in all of the populations studiedin comparison with the most susceptible one ( Table 5), as was observed for abamectin, but with a different susceptibilitystandard. The cartap resistance ratios ranged from 2.3- to 21.9-fold among the T. absoluta populations.

Slopes of the concentration–mortality curves for permethrin and abamectin were relatively similar among the different insectpopulations. However, there was a greater variation in slopes for the insecticides methamidophos and cartap, with somepopulations showing slopes twice as great as those of some others. These high slopes of concentration–mortality curvesprobably reflect a higher homogeneity of response to these insecticides in these populations ( Finney 1971).

Insecticide use varied among sites and the total number of sprays per cultivation cycle per site ranged from seven to 22, thenumber of applications in Uberlândia and Araguari, respectively. Overall number of sprays per cultivation cycle per site forabamectin (mean = 4.3, range = 0–8) and cartap (mean = 4.7, range = 0–8) were greater than for methamidophos (mean = 3.0,range = 0–10) and permethrin (mean = 1.4, range = 0–3). Variation in use of each insecticide was significantly correlated withthe variation in resistance ratio for the same insecticide ( Fig. 2), except for methamidophos (r= 0.36, P= 0.42). Multipleregression analyses showed that the use of other insecticides did not contribute to the resistance ratio of any particularinsecticide. Only the use of the insecticide to which the resistance has been observed provided good regression models, with


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the exception of methamidophos, for which we were unable to obtain any significant model (dferror = 5, F= 9.88, P= 0.02 andr2 = 0.66 for abamectin resistance; dferror = 5, F= 17.08, P= 0.01 and r2 = 0.77 for cartap resistance; dferror = 5, F= 4.23, P=0.10 and r2 = 0.46 for methamidophos resistance; dferror = 5, F= 9.13, P= 0.03 and r2 = 0.65 for permethrin resistance).

Fig. 2 Correlations between number of sprays per cultivation cycle andresistance ratio of T. absoluta for the same insecticide across sevensites.[Normal View ]

Discussion

Among the insecticides investigated here, only resistance to methamidophos had been previously recorded in Chileanpopulations of T. absoluta ( Salazar & Araya 1997). Resistance of T. absoluta to abamectin, cartap and permethrin is reportedhere for the first time. The resistance levels observed in Brazilian populations of the tomato leafminer are relatively low(< 10-fold), but they are possible causes of the control failures with these insecticides ( Souza et al. 1992 ).

There were significant differences in the resistance levels among different populations for each insecticide. Such variability inresistance levels indicates the occurrence of differential selection pressures, genetic diversity in the resistance mechanismsamong the insect populations, or both ( Kerns & Gaylor 1992). The response to abamectin was similar among the resistantinsect populations, but there was greater variability of response among populations for the other insecticides. This may becaused by the different level of use of these compounds in the different areas from where the populations were obtained. Theresistance levels were lower for permethrin and methamidophos, and greater for abamectin and cartap, which may be due to ahigher selection pressure provided by the more intensive use of abamectin and cartap ( Souza et al. 1992 ; Picanço et al. 1995), or the lack of good susceptible standard populations, especially for the insecticides methamidophos and permethrin,underestimating the resistance to these two compounds.

The persistence of an insecticide on a plant leads to the continuous selection of resistant individuals, which may contribute to afaster resistance evolution ( Roush 1989). The lower resistance levels to permethrin in comparison with cartap, compoundsused for about the same length of time in Brazil, might be due to the lower persistence of the former, leading to a lower selectionpressure for resistance on the leafminer populations ( Souza & Reis 1986; Guedes et al. 1994 ). In addition, permethrin ismainly used during the tomato harvest, due to its short pre-harvest interval, unlike cartap, which may have favoured a strongerselection pressure for cartap resistance ( Guedes et al. 1994 ). Despite the low permethrin resistance levels in Brazilianpopulations of T. absoluta observed in our study, the more resistant populations of this insect were obtained from areas of highfrequency of insecticide application and where there were reports of chemical control failures, as in the counties of Araguari andGuiricema ( Souza et al. 1992 ; Picanço et al. 1995 ).

The populations of T. absoluta showed low levels of resistance to methamidophos, similar to those observed for permethrin.This may be due to the relatively lower efficiency of this compound in controlling T. absoluta compared to abamectin and cartap,for example, as reported by Souza et al. 1992 ) . This is probably one of the reasons for its lesser use in comparison with theother compounds, as well as its high toxicity to mammals ( Ware 1994). The resistance levels to methamidophos reported herefor Brazilian populations of T. absoluta resemble those for Chilean populations ( Salazar & Araya 1997).

Abamectin resistance has never been reported in T. absoluta before, despite suspicions of the occurrence of this phenomenonin different populations of this pest as a result of its widespread use, usually in mixture with mineral oil ( Guedes et al. 1995 ;Castelo Branco et al. 1996 ; Castelo Branco et al. 1996 ). The use of mineral oil in mixture with abamectin apparently increasesthe persistence of the insecticidal effects on the plant ,exerting a higher selection pressure on the pest population ( CasteloBranco et al. 1996 ). The use of the insecticide alone does not seem to produce strong selection pressure for resistancebecause of the low doses used in the field and its fast degradation in the environment without bioaccumulation ( Clark et al.1994 ). The low levels of resistance to abamectin observed in our study suggest that the importance of mineral oil in theevolution of abamectin resistance in T. absoluta is probably overestimated. The low variability in response to this insecticideamong different populations of the pest insect is probably a reflection of its widespread use throughout Brazil.

Cartap resistance has not been the object of much attention. The only studies on the subject are those reported by Liu et al.(1982) and Cheng 1988) with the diamondback moth Plutella xylostella. Our results indicate resistance to cartap in Brazilian


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the exception of methamidophos, for which we were unable to obtain any significant model (dferror = 5, F= 9.88, P= 0.02 andr2 = 0.66 for abamectin resistance; dferror = 5, F= 17.08, P= 0.01 and r2 = 0.77 for cartap resistance; dferror = 5, F= 4.23, P=0.10 and r2 = 0.46 for methamidophos resistance; dferror = 5, F= 9.13, P= 0.03 and r2 = 0.65 for permethrin resistance).

Fig. 2 Correlations between number of sprays per cultivation cycle andresistance ratio of T. absoluta for the same insecticide across sevensites.[Normal View ]

Discussion

Among the insecticides investigated here, only resistance to methamidophos had been previously recorded in Chileanpopulations of T. absoluta ( Salazar & Araya 1997). Resistance of T. absoluta to abamectin, cartap and permethrin is reportedhere for the first time. The resistance levels observed in Brazilian populations of the tomato leafminer are relatively low(< 10-fold), but they are possible causes of the control failures with these insecticides ( Souza et al. 1992 ).

There were significant differences in the resistance levels among different populations for each insecticide. Such variability inresistance levels indicates the occurrence of differential selection pressures, genetic diversity in the resistance mechanismsamong the insect populations, or both ( Kerns & Gaylor 1992). The response to abamectin was similar among the resistantinsect populations, but there was greater variability of response among populations for the other insecticides. This may becaused by the different level of use of these compounds in the different areas from where the populations were obtained. Theresistance levels were lower for permethrin and methamidophos, and greater for abamectin and cartap, which may be due to ahigher selection pressure provided by the more intensive use of abamectin and cartap ( Souza et al. 1992 ; Picanço et al. 1995), or the lack of good susceptible standard populations, especially for the insecticides methamidophos and permethrin,underestimating the resistance to these two compounds.

The persistence of an insecticide on a plant leads to the continuous selection of resistant individuals, which may contribute to afaster resistance evolution ( Roush 1989). The lower resistance levels to permethrin in comparison with cartap, compoundsused for about the same length of time in Brazil, might be due to the lower persistence of the former, leading to a lower selectionpressure for resistance on the leafminer populations ( Souza & Reis 1986; Guedes et al. 1994 ). In addition, permethrin ismainly used during the tomato harvest, due to its short pre-harvest interval, unlike cartap, which may have favoured a strongerselection pressure for cartap resistance ( Guedes et al. 1994 ). Despite the low permethrin resistance levels in Brazilianpopulations of T. absoluta observed in our study, the more resistant populations of this insect were obtained from areas of highfrequency of insecticide application and where there were reports of chemical control failures, as in the counties of Araguari andGuiricema ( Souza et al. 1992 ; Picanço et al. 1995 ).

The populations of T. absoluta showed low levels of resistance to methamidophos, similar to those observed for permethrin.This may be due to the relatively lower efficiency of this compound in controlling T. absoluta compared to abamectin and cartap,for example, as reported by Souza et al. 1992 ) . This is probably one of the reasons for its lesser use in comparison with theother compounds, as well as its high toxicity to mammals ( Ware 1994). The resistance levels to methamidophos reported herefor Brazilian populations of T. absoluta resemble those for Chilean populations ( Salazar & Araya 1997).

Abamectin resistance has never been reported in T. absoluta before, despite suspicions of the occurrence of this phenomenonin different populations of this pest as a result of its widespread use, usually in mixture with mineral oil ( Guedes et al. 1995 ;Castelo Branco et al. 1996 ; Castelo Branco et al. 1996 ). The use of mineral oil in mixture with abamectin apparently increasesthe persistence of the insecticidal effects on the plant ,exerting a higher selection pressure on the pest population ( CasteloBranco et al. 1996 ). The use of the insecticide alone does not seem to produce strong selection pressure for resistancebecause of the low doses used in the field and its fast degradation in the environment without bioaccumulation ( Clark et al.1994 ). The low levels of resistance to abamectin observed in our study suggest that the importance of mineral oil in theevolution of abamectin resistance in T. absoluta is probably overestimated. The low variability in response to this insecticideamong different populations of the pest insect is probably a reflection of its widespread use throughout Brazil.

Cartap resistance has not been the object of much attention. The only studies on the subject are those reported by Liu et al.(1982) and Cheng 1988) with the diamondback moth Plutella xylostella. Our results indicate resistance to cartap in Brazilian


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populations of T. absoluta. The observed cartap resistance levels in T. absoluta reached moderate levels (> 10-fold and <100-fold) in four of the populations studied (i.e. Uberlândia, Viçosa, São João da Barra and Araguari), with the highest levelobserved in the population from Araguari (22-fold). Such resistance levels are a probable explanation for the control failures withcartap against T. absoluta reported by França 1993) . However, Castelo Branco et al. 1996 ) suggested that the low efficiencyof cartap against T. absoluta was probably due to a poor application technology. However, our results do not provide supportfor this contention. Nevertheless, poor application may be a contributing factor to the low efficiency of cartap in controllingresistant populations of T. absoluta in some areas. The low to moderate levels of resistance to cartap and the long period ofuse of this insecticide in Brazil suggest that the resistance to cartap has a slow rate of evolution in populations of T. absoluta.

The significant positive correlations between frequency of application and resistance ratio suggest that the variation insusceptibility of T. absoluta populations was caused by local variation in insecticide use. The only exception to this observationwas the insecticide methamidophos, whose resistance ratios were not significantly correlated with its use, probably due to apoor estimation of this insecticide use in São João da Barra, where it is commonly used (10 sprays per cultivation cycle). Thepopulation collected in this site was the most susceptible to this insecticide. After eliminating these data from the correlationanalysis (for methamidophos), there was a significant and positive correlation between frequency of methamidophos applicationand its resistance ratio across the remaining sites (r= 0.88, P= 0.02). The results obtained with the multiple regression did notsuggest any pattern of cross-resistance among the insecticides studied.

In summary, our data indicate that populations of T. absoluta from Brazil show resistance to abamectin, cartap, methamidophosand permethrin, confirming the suspicions raised by other investigators (e.g. Souza et al. 1992 ; França 1993; Guedes et al.1994 ). The resistance levels ranged from low (< 10-fold) to moderate (> 10-fold and < 100-fold) levels for the main insecticidesused for a long time, which suggests a low rate of evolution of this phenomenon in T. absoluta, but also explains some of thecontrol failures observed with the use of these compounds against this insect. Alternatively, the phenomenon might bewidespread among Brazilian populations of T. absoluta, making finding suitable standard susceptible populations difficult andleading to an underestimation of the insecticide resistance levels in this insect. This is one of the few reported cases ofresistance to cartap in insect pests reaching moderate levels in some populations. This finding opposes claims of poorapplication technology as the sole explanation of control failures with the use of this insecticide against T. absoluta. Thecorrelations between insecticide use and resistance ratio across seven sites suggest that local variation in insecticide use wasan important cause of variation in susceptibility. There was no evidence of cross-selection among the insecticides studied.

Acknowledgements

We would like to express our gratitude to Nilton C. Picinato (DuPont) and Norma E. Pereira (Universidade Estadual do NorteFluminense) for providing the T. absoluta populations from Paulínia (SP) and São João da Barra (RJ), respectively; and to theagrochemical companies Iharabrás, Novartis Biociências, Zeneca Agrícola and Bayer for providing the technical gradeinsecticides used in this study. The information about insecticide use provided by growers and State extension personnel wasgreatly appreciated. We also would like to thank A. D. Watt and three anonymous referees for their valuable suggestions.Financial support was provided by FAPEMIG, CNPq and CAPES and is acknowledged here.

References

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Guedes, R.N.C., Picanço, M.C., Guedes, N.M.P., Madeira, N.R. 1995 Sinergismo do óleo mineral sobre a toxicidade deinseticidas para Scrobipalpuloides absoluta (Lepidoptera: Gelechiidae) . Pesquisa Agropecuária Brasileira, 30, 313 318.Guedes, R.N.C., Picanço, M.C., Matioli, A.L., Rocha, D.M. 1994 Efeito de inseticidas e sistemas de condução do tomateiro nocontrole de Scrobipalpuloides absoluta (Meyrick) (Lepidoptera: Gelechiidae) . Anais Da Sociedade Entomológica Do Brasil,23, 321 325.Juvick, J.A., Berlinger, M.J., Bem-David, T., Rudich, J. 1982 Resistance among accessions of genera Lycopersicon andSolanum to four of the main insect pests of tomato in Israel . Phytoparasitica, 10, 145 156.Kay, I.R. & Collins, P.J. 1987 The problem of resistance to insecticides in tropical insect pests. Insect Science and itsApplications, 8, 715 721.Kerns, D.L. & Gaylor, M.J. 1992 Insecticide resistance in field populations of the cotton aphid (Homoptera: aphididae). Journalof Economic Entomology, 85, 1 8.Liu, M.Y., Tzeng, Y.J., Sun, C.N. 1982 Insecticide resistance in the diamondback moth. Journal of Economic Entomology, 75,153 155.Lockwood, J.A., Sparks, T.C., Story, R.N. 1984 Evolution of insect resistance to insecticides: a reevaluation of the roles ofphysiology and behavior. Bulletin of the Entomological Society of America, 30, 41 57.Miranda, M.M.M., Picanço, M., Zanuncio, J.C., Guedes, R.N.C. 1998 Ecological life table of Tuta absoluta (Meyrick)(Lepidoptera: Gelechiidae) . Biocontrol Science and Technology, 8, 597 606.Moore, J.E. 1983 Control of tomato leafminer (Scrobipalpula absoluta) in Bolívia . Tropical Pest Management, 29, 231 238.Muszinski, T., Lavendowski, I.M., Maschio, L.M.A. 1982 Constatação de Scrobipalpula absoluta (Meyrick) (Lepidoptera:Gelechiidae), como praga do tomateiro (Lycopersicon esculentum Mill.), no litoral do Paraná. Anais Da SociedadeEntomológica Do Brasil, 11, 291 292.Picanço, M.C., Guedes, R.N.C., Leite, G.L.D., Fontes, P.C.R., Silva, E.A. 1995 Incidência de Scrobipalpuloides absoluta(Meyrick) (Lepidoptera: Gelechiidae) em tomateiro sob diferentes sistemas de tutoramento e controle químico de pragas .Horticultura Brasileira, 13, 180 183.Picanço, M., Leite, G.L.D., Guedes, R.N.C., Silva, E.A. 1998 Yield loss in trellised tomato affected by insecticidal sprays andplant spacing. Crop Protection, 17, 447 452.Picanço, M.C., Silva, E.A., Lôbo, A.P., Leite, G.L.D. 1996 Adição de óleo mineral a inseticidas no controle de Tuta absoluta(Meyrick) (Lepidoptera: Gelechiidae) e Helicoverpa zea (Bod.) (Lepidoptera: Noctuidae) em tomateiro . Anais Da SociedadeEntomológica Do Brasil, 25, 497 501.Pouey, G.F., Chirinos, D.T., Rivero, G. 1994 Notas sobre Keiferia lycopersicella (Walsingham), (Lepidoptera: Gelechiidae), enVenezuela . Boletin de Entomologia Venezoelana, 9, 203 206.Povolny, D. 1975 On three neotropical species of Gnorimoschemini (Lepidoptera: Gelechiidae) mining Solanaceae . ActaUniversitatis Agriculturae, 23, 379 393.Roush, R.T. 1989 Designing resistance management programs: how can you choose? Pesticide Science, 26, 423 441.Salazar, E.S. & Araya, J.E. 1997 Detección de resistencia a insecticidas em la polilla del tomate. Simiente, 67, 8 22.Sannino, L. & Nicodemo, F. 1979 Su una insolita infestazione di Phthorimea operculella Zell. (Lepidoptera: Gelechiidae) altabacco nel salernitano . Annales Nel Istituto Superior Nel Tabacco Scafati, 5, 125 135.SAS Institute 1997 SAS User's Guide: Statistics, Version 6.12. SAS Institute, Cary, NC, USA.Souza, J.C. & Reis, P.R. 1986 Controle da traça-do-tomateiro em Minas Gerais. Pesquisa Agropecuária Brasileira, 21, 343354.Souza, J.C., Reis, P.R., Salgado, L.O. 1992. Traça Do Tomateiro: Histórico, Reconhecimento, Biologia, Prejuízos E Controle.EPAMIG, Belo Horizonte, MG, Brazil.Tabashnik, B.E. & Roush, R.T. 1990 Introduction. Pesticide Resistance in Arthropods R. T. Roush & B. E. Tabashnik), pp. 1 3.Chapman & Hall. New York.Ware, G.W. 1994. The Pesticide Book. 4th edn. Thomson, Fresno, CA.Accepted 14 April 2000


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Guedes, R.N.C., Picanço, M.C., Guedes, N.M.P., Madeira, N.R. 1995 Sinergismo do óleo mineral sobre a toxicidade deinseticidas para Scrobipalpuloides absoluta (Lepidoptera: Gelechiidae) . Pesquisa Agropecuária Brasileira, 30, 313 318.Guedes, R.N.C., Picanço, M.C., Matioli, A.L., Rocha, D.M. 1994 Efeito de inseticidas e sistemas de condução do tomateiro nocontrole de Scrobipalpuloides absoluta (Meyrick) (Lepidoptera: Gelechiidae) . Anais Da Sociedade Entomológica Do Brasil,23, 321 325.Juvick, J.A., Berlinger, M.J., Bem-David, T., Rudich, J. 1982 Resistance among accessions of genera Lycopersicon andSolanum to four of the main insect pests of tomato in Israel . Phytoparasitica, 10, 145 156.Kay, I.R. & Collins, P.J. 1987 The problem of resistance to insecticides in tropical insect pests. Insect Science and itsApplications, 8, 715 721.Kerns, D.L. & Gaylor, M.J. 1992 Insecticide resistance in field populations of the cotton aphid (Homoptera: aphididae). Journalof Economic Entomology, 85, 1 8.Liu, M.Y., Tzeng, Y.J., Sun, C.N. 1982 Insecticide resistance in the diamondback moth. Journal of Economic Entomology, 75,153 155.Lockwood, J.A., Sparks, T.C., Story, R.N. 1984 Evolution of insect resistance to insecticides: a reevaluation of the roles ofphysiology and behavior. Bulletin of the Entomological Society of America, 30, 41 57.Miranda, M.M.M., Picanço, M., Zanuncio, J.C., Guedes, R.N.C. 1998 Ecological life table of Tuta absoluta (Meyrick)(Lepidoptera: Gelechiidae) . Biocontrol Science and Technology, 8, 597 606.Moore, J.E. 1983 Control of tomato leafminer (Scrobipalpula absoluta) in Bolívia . Tropical Pest Management, 29, 231 238.Muszinski, T., Lavendowski, I.M., Maschio, L.M.A. 1982 Constatação de Scrobipalpula absoluta (Meyrick) (Lepidoptera:Gelechiidae), como praga do tomateiro (Lycopersicon esculentum Mill.), no litoral do Paraná. Anais Da SociedadeEntomológica Do Brasil, 11, 291 292.Picanço, M.C., Guedes, R.N.C., Leite, G.L.D., Fontes, P.C.R., Silva, E.A. 1995 Incidência de Scrobipalpuloides absoluta(Meyrick) (Lepidoptera: Gelechiidae) em tomateiro sob diferentes sistemas de tutoramento e controle químico de pragas .Horticultura Brasileira, 13, 180 183.Picanço, M., Leite, G.L.D., Guedes, R.N.C., Silva, E.A. 1998 Yield loss in trellised tomato affected by insecticidal sprays andplant spacing. Crop Protection, 17, 447 452.Picanço, M.C., Silva, E.A., Lôbo, A.P., Leite, G.L.D. 1996 Adição de óleo mineral a inseticidas no controle de Tuta absoluta(Meyrick) (Lepidoptera: Gelechiidae) e Helicoverpa zea (Bod.) (Lepidoptera: Noctuidae) em tomateiro . Anais Da SociedadeEntomológica Do Brasil, 25, 497 501.Pouey, G.F., Chirinos, D.T., Rivero, G. 1994 Notas sobre Keiferia lycopersicella (Walsingham), (Lepidoptera: Gelechiidae), enVenezuela . Boletin de Entomologia Venezoelana, 9, 203 206.Povolny, D. 1975 On three neotropical species of Gnorimoschemini (Lepidoptera: Gelechiidae) mining Solanaceae . ActaUniversitatis Agriculturae, 23, 379 393.Roush, R.T. 1989 Designing resistance management programs: how can you choose? Pesticide Science, 26, 423 441.Salazar, E.S. & Araya, J.E. 1997 Detección de resistencia a insecticidas em la polilla del tomate. Simiente, 67, 8 22.Sannino, L. & Nicodemo, F. 1979 Su una insolita infestazione di Phthorimea operculella Zell. (Lepidoptera: Gelechiidae) altabacco nel salernitano . Annales Nel Istituto Superior Nel Tabacco Scafati, 5, 125 135.SAS Institute 1997 SAS User's Guide: Statistics, Version 6.12. SAS Institute, Cary, NC, USA.Souza, J.C. & Reis, P.R. 1986 Controle da traça-do-tomateiro em Minas Gerais. Pesquisa Agropecuária Brasileira, 21, 343354.Souza, J.C., Reis, P.R., Salgado, L.O. 1992. Traça Do Tomateiro: Histórico, Reconhecimento, Biologia, Prejuízos E Controle.EPAMIG, Belo Horizonte, MG, Brazil.Tabashnik, B.E. & Roush, R.T. 1990 Introduction. Pesticide Resistance in Arthropods R. T. Roush & B. E. Tabashnik), pp. 1 3.Chapman & Hall. New York.Ware, G.W. 1994. The Pesticide Book. 4th edn. Thomson, Fresno, CA.Accepted 14 April 2000


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Abamectin resistance and synergism in Brazilian populations of Tuta absoluta (Meyrick)(Lepidoptera: Gelechiidae)

(Keywords: tomato leafminer, Brazil, insecticide resistance, diethyl maleate, piperonyl butoxide, triphenylphosphate)

H. A. A. SIQUEIRA, R. N. C. GUEDES*, D. B. FRAGOSO and L. C. MAGALHAÄES

Departamento de Biologia Animal, Universidade Federal de VicË osa, VicË osa, MG 36571-000, Brazil

Abstract. Failures in the control of the tomato leafminer Tuta absoluta(Meyrick) by means of abamectin in Brazil, and a recent report ofabamectin resistance in Brazilian populations of this pest species, led tothe investigation of the possible involvement of detoxification enzymesusing insecticide synergists. Resistance to abamectin was observed inall populations when compared with the standard susceptible popula-tion, with resistance ratios ranging from 5.2- to 9.4-fold. Piperonylbutoxide was the most efficient synergist with abamectin synergismratios ranging from 3.0- to 5.3-fold and providing significant resistancesuppression, but complete suppression of abamectin resistance wasonly obtained in one population of T. absoluta. Triphenylphosphate wasan abamectin synergist which was not as efficient as piperonyl butoxide,but it provided complete suppression of abamectin resistance in four ofthe six resistant populations studied, suggesting a major involvement ofesterases as an abamectin resistance mechanism in these populations.The importance of cytochrome P450, inhibited by piperonyl butoxide,seems secondary to esterases. Diethyl maleate also synergizedabamectin in nearly all populations, but provided only partial suppres-sion of abamectin resistance in the leafminer populations studied.Therefore, glutathione-S-transferases seem to be of minor importanceas an abamectin resistance mechanism in Brazilian populations of T.absoluta.

1. Introduction

Brazil is the eighth greatest producer of tomatoes in theworld, with 60,000 ha of the crop grown annually, and anaverage productivity of 44 t.ha-1 (FAO, 1994). Tomato produc-tion for fresh consumption is the most important source ofincome for small producers in several regions of the country.However, this vegetable crop is often severely damaged bypests in the tropics, and pesticides are intensively used tocontrol insects and pathogens in Brazil (Gravena, 1991;Makishima, 1991; PicancËo et al., 1998). This situation substan-tially increases the crop production cost and leads to humanhealth and environmental problems in addition to selecting forresistance to pesticides. The tomato leafminer, Tuta (=Scrobi-palpuloides) absoluta (Meyrick) (Lepidoptera: Gelechiidae), isconsidered to be one of the most important pests of tomatoproduction in Brazil (Souza and Reis, 1986; Souza et al., 1992).It is an oligophagous insect, distributed throughout the Neo-tropical region, attacking solanaceous plants. It is of majorimportance in Venezuela, Colombia, Chile, Equator, Bolivia,Argentina, Peru (Povolny, 1975), and Uruguay (Carballo et al.,1981). Its occurrence has been reported even in Japan (Nakanoand Paulo, 1983).

It has been a serious problem to tomato production in Brazilsince its introduction and rapid spread in the 1980s. Thedamage caused by T. absoluta resembles that caused by otherGelechiidae such as Keiferia lycopersicella (Wals.) in Centraland North America, and Phthorimaea operculella (Zell.) in theAmericas, Europe, Africa and Asia (Sannino and Nicodemo,1979; Juvick et al., 1982; Abbas et al., 1993; Ebora et al., 1994;Pouey et al., 1994). At high densities it can cause severe yieldlosses (Souza et al., 1992; PicancËo et al., 1998).

Chemical control has been the primary control strategy forthis insect since the early 1980s (Souza and Reis, 1986), withsome farmers still making up to 36 insecticide applicationsduring the crop cycle (PicancËo et al., 1995). Producers haveobserved insecticide failures in controlling this pest andresearchers have shown reduced insecticide activity in the field(Souza et al., 1992; FrancËa, 1993; Guedes et al., 1994),suggesting the development of resistant populations to com-pounds used against T. absoluta (GoncË alves et al., 1994).

Abamectin was first used around 1990 due to control failureswith other insecticides (Castelo Branco, 1990). Studies onabamectin resistance in T. absoluta populations have not yetbeen carried out, despite reports of resistance in this species toother insecticides in Chile (Salazar and Araya, 1997). However,studies on abamectin resistance have been carried out inresistant strains of house flies (Musca domestica L.) (Roush andWright, 1986), German cockroaches (Blattella germanica (L.))(Cochran, 1990, 1994), Colorado potato beetle (Leptinotarsadecemlineata (Say)) (Argentine and Clark, 1990; Argentine etal., 1992), and spider mites (Tetranichus urticae Koch and T.mcdanuli McGregor) (Campos et al., 1995; Beers et al., 1998).No cross-resistance (i.e., resistance to two or more insecticidesdue to the same mechamism) to abamectin was detected inthese studies (Clark et al., 1995). Among lepidopteran pests,only the diamondback moth, Plutella xylostella, has beensubjected to more intense investigation of abamectin resistance(Abro et al., 1988; Iqbal and Wright, 1997). Resistancemechanisms to abamectin have been studied in a few species,where several major resistance mechanisms and some minorfactors have been implicated (Clark et al., 1995).

The aim of this study was to survey abamectinresistance in Brazilian populations of T. absoluta and toassess the possible involvement of detoxification enzymes in

International Journal of Pest ManagementISSN 0967-0874 print/ISSN 1366-5863 online Ó 2001 Taylor & Francis Ltd

http://www.tandf.co.uk/journalsDOI: 10.1080/09670870110044634

*To whom correspondence should be addressed. Fax: +55 (31)3899-2537; e-mail: [email protected]

INTERNATIONAL JOURNAL OF PEST MANAGEMENT, 2001, 47(4) 247±251

abamectin resistance using insecticide synergists in in vivo’assays.

2. Material and methods

Five populations of T. absoluta from the State of MinasGerais, one from SaÄo Paulo State and another from Rio deJaneiro State, were used in this study (Table 1). A fieldpopulation collected from UberlaÃndia County, State of MinasGerais, was used as an abamectin susceptible standardpopulation because it was obtained from a site where thisinsecticide had not been used and it was reported as apopulation susceptible to this insecticide in a previous investiga-tion (Siqueira, 1999). Colonies of T. absoluta were establishedfrom at least 200 larvae obtained from heavily infested leavesfromeach sampling site. The individual populations were rearedon tomato plants of variety Santa Clara, without insecticideexposure, enclosed in cages and maintained under greenhouseconditions at a temperature and daylength varying from 22 to288C and from 10 to 14 h respectively, during the study period.The colonies were maintained for two generations in thelaboratory before starting the bioassays.

In vivo bioassays, using insecticide-impregnated filter paper(9 cm diameter) placed in Petri dishes (9 cm diameter61.5 cmheight), were carried out. Technical grade abamectin (NovartisBiocieÃncias, SaÄo Paulo, SP) was used in the investigation. Thethree synergists used were diethyl maleate, piperonyl butoxideand triphenylphosphate (Aldrich Chemical Co., Milwauke, WI,USA). Diethyl maleate is an inhibitor of glutathione-S-trans-ferases, while piperonyl butoxide and triphenylphosphate areinhibitors of cytochrome P450-dependent monooxygenases and

esterase respectively (Raffa and Priester, 1985; Bernard andPhilogeÁne, 1993).

Three replicates with 20 second instar larvae of T. absolutawere used at each insecticide concentration. For each concen-tration±mortality regression line, six to seven different insecticideconcentrations were applied; a control treatment of acetonealone was included and used for correcting mortality in the othertreatments. On each replicate of each concentration we used afilter paper impregnated with 1 ml of insecticide dissolved inacetone. Insecticide concentrations were calculated as mg a.i./cm2 of treated surface. Insects were counted as dead if theywere unable to walk. The synergist bioassays followed the samemethodology described above using a insecticide:synergistproportion of 1:10. The synergists were applied on filter paperwith dried insecticide residues at the specified concentration,where 1 ml of the synergist solution proportional to eachinsecticide concentration was applied. No mortality was ob-served in preliminary assays with the synergists used alone atthe highest concentrations used in this investigation when inmixture with abamectin. Concentration±mortality data weresubjected to probit analysis (PROC PROBIT, SAS Institute,1987).

3. Results

The concentration±mortality regression lines were obtainedfor all combinations of insecticide or insecticide + synergist andevery insect population under study (tables 2±5). There wassignificant variation on the susceptibility among the insectpopulations studied in response to abamectin. The resistanceratios were calculated by dividing the LC50 of the mostsusceptible population (UberlaÃndia) to this insecticide by theLC50 of the other insect populations (table 2). The LC50 of thesusceptible population was significantly smaller than those ofthe other populations based on the criterion of failure of 95% CLto overlap (table 2). The resistance ratio among the resistancepopulations ranged from 5.2- to 9.4-fold. Slopes of theconcentration±mortality curves for abamectin were relativelysimilar among the different insect populations, showing similarhomogeneity of response for all populations.

Piperonyl butoxide synergized abamectin for all populations,based on the criterion cited above, except for the UberlaÃndiapopulation which was slightly antagonized. Resistance suppres-sion was complete for the PaulõÂnia population, and nearlycomplete for the remaining populations (table 3). Diethyl maleate

H. A. A. Siqueira et al.248

Table 1. Origin and year of collection of leafminer populations (T.

absoluta)

County State LocalMonth/

Collection year

Araguari Minas Gerais Field 08/1998Guiricema Minas Gerais Field 09/1998Lavras Minas Gerais Field 08/1998

UberlaÃndia Minas Gerais Field 04/1998VicËosa Minas Gerais Field 10/1997

SaÄo JoaÄo da Barra Rio de Janeiro Greenhouse 08/1997PaulõÂnia SaÄo Paulo Greenhouse 08/1998

Table 2. Relative susceptibility of populations of tomato leafminer (Tuta absoluta) to abamectin

Population n Slope+SEMLC50 (95% CL)(mg a.i./cm2)

LC90 (95% CL)(mg a.i./cm2)

Resistanceratioa w

2 P

UberlaÃndia 360 0.80+0.10 0.97 (0.87 ± 1.09) 2.40 (1.99 ± 3.14) Ð 4.34 0.36 NSPaulõÂnia 361 0.76+0.12 5.00 (4.21 ± 5.81) 18.22 (14.51 ± 25.09) 5.16 3.30 0.51 NSGuiricema 360 0.67+0.06 5.87 (4.90 ± 6.96) 21.92 (16.78 ± 32.34) 6.04 2.80 0.59 NSSaÄo JoaÄo da Barra 420 0.45+0.03 5.96 (4.51 ± 7.52) 48.74 (35.13 ± 76.67) 6.14 1.19 0.95 NSVicËosa 421 0.49+0.04 6.76 (5.28 ± 8.37) 47.15 (34.80 ± 71.20) 6.97 1.93 0.86 NSLavras 360 0.67+0.08 8.31 (7.10 ± 9.87) 34.66 (25.14 ± 56.57) 8.57 0.48 0.98 NSAraguari 360 0.63+0.09 9.09 (7.68 ± 10.92) 35.97 (25.33 ± 65.02) 9.37 6.79 0.15 NS

aLC50 resistant/LC50 susceptible.

NS, not significant.

synergized significantly the populations from Araguari, Lavras,SaÄo JoaÄo da Barra and VicË osa; however, it had no effect on thepopulations from PaulõÂnia and Guiricema and even antagonizedabamectin in the UberlaÃndia population at its LC50. Resistancesuppression was smaller than with piperonyl butoxide for theAraguari, Lavras, SaÄo JoaÄo da Barra and VicËosa populations(table 4). There was no resistance suppression for the PaulõÂniaand Guiricema populations. Triphenylphosphate synergized allpopulations, except the one from UberlaÃndia, in which a slightantagonism to abamectin was observed (table 5). This synergistcompletely suppressed abamectin resistance in four populationsand nearly did so in the remaining two among the six testedpopulations.

Synergising insecticides usually results in steeper concen-tration±response curves if the population is heterogeneous for

resistance. This was generally the case in our study, which isexpected for field-collected populations. However there were afew exceptions, mainly for triphenylphosphate, where no changein slope was observed probably reflecting a higher homogeneityof response to this synergist in the populations studied.

4. Discussion

T. absoluta resistance to abamectin was reported bySiqueira (1999). The occurrence of this phenomenon in differentpopulations of this pest was suspected as a result of itswidespread use, usually in a mixture with mineral oil (Guedes etal., 1995; Castelo Branco and FrancË a, 1996; Castelo Branco etal., 1996). The low levels of resistance to abamectin observed inour study suggest that the importance of mineral oil in the

Abamectin resistance and synergism in T. absoluta 249

Table 3. Relative susceptibility of populations of tomato leafminer (Tuta absoluta) to abamectin+ piperonyl butoxide (1:10)


Resistanceratioa

Synergismratio b w2 P

UberlaÃndia 360 1.25+0.11 1.30 (1.19 ± 1.42) Ð 0.75 2.51 0.64 NSPaulõÂnia 340 1.04+0.21 1.24 (1.04 ± 1.40) 0.95 4.03 5.47 0.32 NSGuiricema 360 1.75+0.19 1.94 (1.65 ± 2.24) 1.49 3.03 8.74 0.07 NSSaÄo JoaÄo da Barra 360 1.22+0.23 1.68 (1.53 ± 1.84) 1.29 3.55 4.68 0.24 NSVicËosa 360 0.89+0.08 2.04 (1.77 ± 2.31) 1.57 3.31 5.53 0.24 NSLavras 340 1.40+0.20 1.58 (1.44 ± 1.72) 1.22 5.26 3.18 0.53 NSAraguari 361 0.61+ 0.07 2.70 (2.08 ± 3.30) 2.08 3.37 3.21 0.52 NS

aResistance Ratio (= LC50 synergized resistant /LC50 synergized susceptible).bSynergism Ratio (= LC50 unsynergized abamectin/ LC50 synergized abamectin).


Table 4. Relative susceptibility of populations of tomato leafminer (Tuta absoluta) to abamectin + diethyl maleate (1:10)


Resistanceratio a


UberlaÃndia 366 1.47+0.20 1.84 (1.68 ± 1.99) Ð 0.53 4.49 0.34 NSPaulõÂnia 367 0.83+0.04 4.03 (3.45 ± 4.63) 2.19 1.24 5.12 0.28 NSGuiricema 400 0.55+0.08 4.84 (3.97 ± 6.07) 2.63 1.21 8.89 0.11 NSSaÄo JoaÄo da Barra 362 1.01+0.14 2.73 (2.43 ± 3.05) 1.48 2.18 6.23 0.18 NSVicËosa 360 0.89+0.10 2.52 (2.18 ± 2.86) 1.37 2.68 4.56 0.34 NSLavras 360 1.34+0.17 2.19 (2.01 ± 2.39) 1.19 3.79 5.22 0.27 NSAraguari 363 0.89+0.08 6.30 (5.43 ± 7.13) 3.42 1.44 3.80 0.43 NS



Table 5. Relative susceptibility of populations of tomato leafminer (Tuta absoluta) to abamectin + triphenylphosphate (1:10)


Resistanceratio a


UberlaÃndia 343 0.89+0.30 1.95 (1.67 ± 2.25) Ð 0.50 6.70 0.15 NSPaulõÂnia 361 0.57+0.08 2.18 (1.65 ± 2.70) 1.12 2.29 7.05 0.76 NSGuiricema 360 0.71+0.08 4.06 (3.37 ± 4.77) 2.08 1.45 1.30 0.86 NSSaÄo JoaÄo da Barra 363 0.76+0.09 2.28 (1.91 ± 2.65) 1.17 2.61 1.88 0.13 NSVicËosa 360 0.64+0.08 2.17 (1.71 ± 2.61) 1.11 3.12 6.16 0.19 NSLavras 366 1.29+0.19 2.21 (2.02 ± 2.42) 1.13 3.76 5.09 0.28 NSAraguari 362 0.67+0.05 5.06 (4.12 ± 6.03) 2.60 1.80 2.82 0.59 NS



evolution of abamectin resistance in T. absoluta is probablyoverestimated, even though it does provide support for thecontention that abamectin resistance is one of the causes ofcontrol failures of this insecticide observed in field. The intensiveuse of abamectin in T. absoluta control programmes seems notto have been enough to select highly resistant strains. This isprobably due to the low dose of abamectin used in the field andits fast degradation in the environment without bioaccumulationwhich do not seem to provide strong selection pressure forresistance (Clark et al., 1995).

Besides using enzymes to maintain their normal home-ostasis, insects may also use them for protection againstxenobiotics. Among the known insecticide resistance mechan-isms, it is not surprising that enhanced activity of detoxificationenzymes is one of the most commonmechanisms of resistanceto insecticides (Scott, 1990a). Insect detoxification enzymes areimportant resistance mechanisms and synergists are helpful inproviding preliminary evidence of their involvement as resis-tance mechanisms (Brindley and Selim, 1984; Scott, 1990b;Bernard and PhilogeÁne, 1993; Ishaaya, 1993). In this study,abamectin toxicity was enhanced by the synergists diethylmaleate, piperonyl butoxide and triphenyl phosphate whichrespectively inhibit the detoxification enzymes glutathione-S-transferases, cytochrome P450-dependent monooxygenases,and esterases (Raffa and Priester, 1985; Bernard and Philo-geÁne, 1993), providing some interesting information regardingabamectin resistance mechanisms in this insect-species.

Piperonyl butoxide nearly completely suppressed the resis-tance to abamectin in all populations, except for the PaulõÂniapopulation of T. absoluta where the suppression was complete.The synergism to abamectin by piperonyl butoxide suggests anenhanced cytochrome P450-dependentmonooxygenase activityin this insect species as an abamectin resistance mechanism.This effect by piperonyl butoxide has been observed in otherarthropod species. The involvement of monooxygenases inabamectin resistance was observed in Colorado potato beetle,house flies, two-spotted spider mites, Spodoptera littoralis andHelicoverpa armigera (Scott, 1989; Christie and Wright, 1990;Argentine et al., 1992; Campos et al., 1996).

Gluthatione-S-transferases are also probably involved inabamectin resistance in T. absoluta. Our results indicate partialsuppression of abamectin resistance by diethyl maleate whichinhibit gluthatione-S-transferases. However this seems to be amechanism of minor importance. Argentine et al. (1992) foundthat gluthatione-S-transferases were not important as a resis-tance mechanism in L. decemlineata and carboxylesterasespossibly play an important role in abamectin resistance in thisspecies. Despite the occurrence of partial suppression by diethylmaleate in the populations from PaulõÂnia and Guiricema, thesynergistic effect was not significant. Triphenylphosphate andpiperonyl butoxide are stronger synergists to abamectin thandiethyl maleate suggesting enhanced detoxification by es-terases and cytochrome P450-dependent monooxygenases inpopulations of T. absoluta resistant to abamectin.

Triphenylphosphate completely suppressed abamectin re-sistance in four T. absoluta populations (from Lavras, PaulõÂnia,SaÄo JoaÄo da Barra, and VicË osa) and provided partial suppres-sion in two populations (from Araguari and Guiricema). Theseresults suggest a major involvement of esterases as anabamectin resistance mechanism in Brazilian populations of T.

absoluta, with cytochrome P450-dependent monooxygenasesprobably playing a secondary role in addition to gluthatione-S-transferases as a mechanism of minor importance. Thecoexistence of different resistance mechanisms in the sameinsect populations suggests an oligo or polygenic basis forabamectin resistance in these populations.

The use of synergists in insecticide resistance managementprogrammes has been frequently suggested (e.g. Oppenoorth,1985; Guedes, 1991; DenholmandRowland, 1992; Bernard andPhilogeÁne, 1993). However theymay not be useful formanagingabamectin resistance in Brazilian populations of T. absoluta,because of the likely occurrence of multiple resistance mechan-isms. Nonetheless, synergists can be important tools formanaging T. absoluta populations lacking insecticide cross-resistance. Resistance to abamectin is polyfactorial in both L.decemlineata and M. domestica, which has resulted in severalmajor resistance mechanisms (e.g. excretion, oxidative meta-bolism, penetration) and minor factors (e.g. altered target site,conjugation, esteratic hydrolysis/sequestration) associated withthe phenomenon (Clark et al., 1995). The resistance toabamectin in T. absoluta populations may be oligo- or evenpolyfactorial, but further investigations are necessary to betterassess this possibility.

Acknowledgements

We would like to express our gratitude Nilton C. Picinato(DuPont) and Norma E. Pereira (Universidade Estadual doNorte Fluminense) for providing the T. absoluta population fromPaulõÂnia (SP) and SaÄo JoaÄo da Barra (RJ) respectively; andNovartis BiocieÃncias for providing the technical grade abamectinused in this study. Financial support was provided by FAPEMIG,CNPq and CAPES and is acknowledged here.

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Abamectin resistance and synergism in T. absoluta 251

January - February 2005 Neotropical Entomology 34(1) 113

CROP PROTECTION

Insecticide Resistance in Argentine Populations of Tuta absoluta (Meyrick)(Lepidoptera: Gelechiidae)

MARCELA M.M. LIETTI1, EDUARDO BOTTO2 AND RAÚL A. ALZOGARAY3

1Cátedra de Zoología Agrícola, Facultad de Ciencias Agrarias, Universidad Nacional de Rosario (U.N.R.)C.C. 14, (S2125ZAA) Zavalla, Santa Fe, Argentina. E-mail: [email protected]

2Insectario de Investigaciones para Lucha Biológica, IMYZA-CNIA, INTA. C.C. 25, (1712)Castelar, Buenos Aires, Argentina

3Centro de Investigaciones de Plagas e Insecticidas (CIPEIN-CITEFA/CONICET)J. B. de La Salle 4397, (B1603ALO) Villa Martelli, Buenos Aires, Argentina

E-mail: [email protected]

Neotropical Entomology 34(1):113-119 (2005)

RESUMO - A traça-do-tomateiro, Tuta absoluta (Meyrick), é uma das pragas chaves no tomateiro naArgentina. O controle químico tem sido o principal método de controle empregado a partir da suadispersão nos anos 70. Contudo, tem-se observado uma redução na eficácia de alguns dos inseticidasrecomendados a partir da década de 80. O objetivo deste trabalho foi estudar a toxicidade de trêsinseticidas amplamente usados no controle químico de T. absoluta (abamectina, deltametrina emetamidofós) em larvas de uma população susceptível de laboratório (CASTELAR) e duas populaçõescolectadas em casa de vegetação (ROSARIO e BELLA VISTA). Inseticidas foram diluídos em acetonae aplicados topicamente na região dorsal mediana do abdome de larvas no segundo dia do quartoestágio larval. Para cada inseticida estimou-se o LD50 e calculou-se o Nível de Resistência (NR = LD50decada população de casa de vegetação/LD50 população de laboratório). As populações de ROSARIO eBELLA VISTA mostraram os seguintes NRs: > 68.38 para deltametrina; 2.48 e 3.49 para abamectina,respetivamente; e 0.79 e 0.86 para metamidofós, respetivamente. A resistência a deltametrina observadaem ROSARIO pode ser resultante da alta pressão seletiva exercida pelos piretróides nessa localidade.A resistência incipiente a abamectina detectada em BELLA VISTA pode ter sido causado pelo usofreqüente do inseticida nessa localidade ou pode estar associada à variação natural.

PALAVRAS-CHAVE: Traça-do-tomateiro, deltametrina, abamectina, metamidofós, resistência a inseticidas

ABSTRACT - The tomato leafminer, Tuta absoluta (Meyrick), is one of the key pests of tomato inArgentina. Since its dispersal in the 1970s, chemical control has been the main method of controlling it.However, reduced efficacy of some of the recommended insecticides has been observed since the1980s. The aim of this work was to study the toxicity of three insecticides widely used in chemicalcontrol of T. absoluta (abamectin, deltamethrin and methamidophos) on larvae from a laboratorysusceptible population (CASTELAR) and two greenhouse populations (ROSARIO and BELLA VISTA).Insecticides were dissolved in acetone and topically applied to the mid-dorsal abdominal region of two-day old 4th instar larvae. LD50 values were estimated and the Resistance Ratio (RR) for each insecticidewas calculated (RR = LD50 value of each greenhouse population/LD50 value of the susceptiblepopulation). ROSARIO and BELLA VISTA populations showed the following RRs values: > 68.38 fordeltamethrin; 2.48 and 3.49 for abamectin, respectively; and 0.79 and 0.86 for metamidophos, respectively.Deltamethrin resistance observed in ROSARIO could be due to the high selective pressure exerted bypyrethroids in this location. Deltamethrin resistance in BELLA VISTA is more difficult to explain,because pyrethroids were scarcely used in the greenhouse where the insects were sampled. The incipientabamectin resistance detected in the BELLA VISTA population could result from the frequent use ofthis insecticide in this location, although natural variation can not be discarded.

KEY WORDS: Tomato leafminer, deltamethrin, abamectin, metamidophos, insecticide resistance

Resistência a Inseticidas em Populações Argentinas de Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

114 Insecticide Resistance in Argentine Populations of Tuta absoluta (Meyrick)... Lietti et al.

Tomato crop is the second horticultural crop in Argentina,with a harvested area of 24,000 ha and an average yield of30,833 kg/ha (FAO 1996). Seventy per cent of the productiondestination is for consumption in natura and the rest isindustrialized (Gómez Riera 1992). Tomato produced undergreenhouses as well as in outdoor areas for consumption innatura brings the highest gross financial return to farmers inthe Litoral Region (Buenos Aires, Corrientes and Santa Feprovinces) (Stoppani & Rodríguez 1992).

The tomato leafminer, Tuta absoluta (Meyrick), is aneotropical oligophagous insect, which attacks solanaceouscrops. Since the 1960s it has become one of the key pests oftomato crops in many South American countries (Souza etal. 1983, Larraín 1986, IAN 1994). A fruit importation fromChile may have introduced it to Mendoza province(Argentina) in April 1964 (Bahamondes & Mallea 1969);dissemination to other tomato production regions occurredthrough fruit commercialization (Benavent et al. 1978, Cáceres1992, Riquelme 1993).

Larvae can damage tomato plants during all growth stages,producing large galleries in their leaves, burrowing stalks,apical buds, green and ripe fruits (Cáceres 1992, IAN 1994). Itcan cause important yield losses in different productionregions and under diverse production systems (Benavent etal. 1978, Cáceres 1992).

Since its introduction, chemical control has been the mainmethod of control used against T. absoluta in all productionregions in Argentina. Horticultural growers have tried todecrease its injure applying insecticides two times a weekduring a single cultivation period. Effective chemical controlwas difficult to achieve because of the mine-feedingbehaviour of larvae, lack of a threshold action, and deficientspraying technology.

Initially, the only insecticides used against tomatoleafminer in Argentina were organophosphates, which weregradually replaced by pyrethroids during the 1970s. In theearly 1980s, cartap, alternated with pyrethroids, andthiocyclam were introduced with the former showing excellentefficacy at that moment. During the 1990s, insecticides withnovel sites of action such as abamectin, acylurea insectgrowth regulators, spinosad, tebufenozide and chlorfenapyrwere introduced (Galarza & Larroque 1984, Polack 1999,Cáceres 2000).

Reports of insecticide resistance development inpopulations of T. absoluta were scarce. A decrease in thecontrol efficiency of organophosphorous insecticides wasobserved in Bolivia and Chile, which could be satisfactorilycontrolled by pyrethroids (Moore 1983, Larraín 1986).Recently, the existence of resistance to organophosphatesand pyrethroids in Chile (Salazar & Araya 1997, 2001) and toabamectin, cartap, methamidophos and permethrin in Brasil(Siqueira et al. 2000, 2001) were reported.

The suspicion about the development of resistance inArgentine populations of T. absoluta has been present sincethe 1980s, when growers and agronomic advisers observedthat some of the compounds recommended for its controlwere loosing its effectiveness in the field. Apparently, theloss in effectiveness has not occurred with the same intensityand to the same compounds in all tomato producing regions.

Nevertheless, the susceptibility of different populations todistinct active ingredients has not yet been determined.Owing to a decreasing activity of some insecticides usedagainst T. absoluta and the report of resistant populationsin Chile and Brasil, it is necessary to detect and quantifythe resistance to the main insecticides used for its controlin Argentina.

The objective of this work was to evaluate the toxicityof abamectin, deltamethrin and methamidophos to alaboratory-susceptible and two greenhouse populations ofT. absoluta, in order to establish if insecticide resistancehas developed in the last ones. The three insecticides usedin this study are currently registered and widely used byfarmers as chemical control of T. absoluta and other tomatopests in Argentina (CASAFE 2001).

Material and Methods

Biological Material. A susceptible population of T. absoluta(CASTELAR population), reared since 1993 withoutexposure to insecticides, was provided by the Insectario deInvestigaciones para Lucha Biológica, IMIZA, CNIA-INTA.(Castelar, Buenos Aires Province).

Greenhouse individuals of T. absoluta were collectedfrom tomato crops cultivated in the Módulo Experimentalde Nuevas Tecnologías (Rosario, Santa Fe Province)(ROSARIO population) and in the Experimental Station,INTA (Bella Vista, Corrientes Province) (BELLA VISTApopulation). Both populations came from experimentalcrops grown under greenhouses and exposed to intensechemical treatments to maintain them free of pests. Thegreenhouses are made of wood and covered by plastic.The sides of them are lifted, whenever required, forregulating the temperature inside it. Information aboutinsecticides used in each site during the current cultivationperiod was obtained. Individuals from both the susceptibleand the greenhouse populations were separately rearedon greenhouse organically-grown tomato plants(Lycopersicon esculentum Mill) cv. Presto (Petoseed ®)in a controlled environment room at 25 ± 2°C and under aphotoperiod of 14:10 L:D. The experimental work was doneon two-day old 4th larval stage.

Chemicals. The insecticides used in this study wereabamectin 94% (Chemotecnica, Argentina), deltamethrin >99% (Roussell-Uclaf, France) and methamidophos 68%(Bayer, Argentina). Acetone pro-analysis (Merck,Argentina) was used as solvent.

Bioassay. Insecticides were topically applied to the mid-dorsal abdominal region of the larvae using a micro syringeprovided with a dispenser. Each insect received 0.2 µl of asolution of insecticide in acetone. Control groups weretopically treated with acetone alone. Five to seven doses ofeach compound and 15 to 20 larvae for each dose were usedto estimate the Lethal Dose 50% (LD50) values. Three tofive independent replicates for each bioassay were done.Data of the different replicates were pooled when theconfidence limits of their respective LD50 overlapped.


After treatment, the larvae were individually placed in 3 cm3

plastic vials (13 x 35 mm) in a controlled environment room at 27± 2°C and under a photoperiod of 14:10 (L:D). Mortality wasrecorded 24h after treatment under stereoscopic microscope (10x).Larvae were considered as dead when they were not able tomove back to ventral position after being placed on their dorsum.

The LD50 values were calculated using the Probit method(Lichtfield & Wilcoxon 1949). In all cases, differences betweenvalues were considered significant (P < 0.05) if the respective95% confidence limits did not overlap.

Resistance Ratios (RRs) values were calculated bydividing the LD50 value of each greenhouse population bythe LD50 value of the susceptible population. Confidencelimits of RRs were calculated according to Robertson &Preisler (1992). RRs were considered significantly differentfrom 1 (P < 0.05) when their 95% confidence limits did notinclude 1.

Results

Fig. 1 shows the dose-response relationship for abamectinand metamidophos in an insecticide susceptible(CASTELAR) and two greenhouse populations (BELLAVISTA and ROSARIO) of T. absoluta. The DL50 and RRsvalues are shown in Table 1. The LD50 value of deltamethrinwas 0.35 µg/larva for the CASTELAR population. The LD50values of deltamethrin could not be calculated for the BELLAVISTA and ROSARIO populations because the highest doseapplied (24 mg/larva, which is near the solubility limit of theinsecticide) caused only 31.9 and 18.3% of mortality,respectively. The RRs values were > 68.4 in both cases,indicating a high resistance to deltamethrin.

The LD50 values of methamidophos were 0.81, 0.70 and0.65 µg/larva for the CASTELAR, BELLA VISTA andROSARIO populations, respectively. No significantdifferences among those values were observed (P > 0.05).The RRs values were not significantly different from 1 (P >0.05). Hence, no resistance to this insecticide was observedin the greenhouse populations.

The LD50values of abamectin were 0.16, 0.57 and 0.41 ηg/larva for the CASTELAR, BELLA VISTA and ROSARIOpopulations, respectively. The BELLA VISTA LD50 value wassignificantly higher than the CASTELAR one (P < 0.05), butthere was no significant difference between the ROSARIOand CASTELAR values (P > 0.05). BELLA VISTA andROSARIO RRs were 3.49 and 2.48, respectively. Both valuesdiffered significantly from 1 (P < 0.05). These results indicateda slight resistance to abamectin in the BELLA VISTApopulation.

Discussion

There are very few studies of insecticide resistance in T.absoluta. Salazar & Araya (1997) reported resistance todeltamethrin, metamidophos, esfenvalerate, lambda-cyhalothrin and mevinphos in Chilean populations of thispest. Studying different larval stages from several localities,they found RRs values ranging from 2.2 to 8.2 for deltamethrin,from 1.6 to 3.9 for metamidophos, from 1.9 to 12.6 for

Figure 1. Dose-response regressions for metamidophosand abamectin topically applied on T. absoluta 4th larval stagefrom a laboratory (CASTELAR) and two greenhousepopulations (ROSARIO and BELLA VISTA).

dose (µg/insect)0,1 1,0 10,0

mor

talit

y (%

)

10

20304050607080

90

95

9899

CASTELAR (1)

BELLA VISTA (3)ROSARIO (2)

231metamidophos

dose (ng/insect)0,01 0,10 1,00 10,00

mor

talit

y (%

)

10

20

3040506070

80

90

95

98CASTELAR (1)

BELLA VISTA (3)ROSARIO (2)

2 31 abamectin

Metamidophos

CASTELAR (1)ROSARIO (2)BELLA VISTA (3)

Abamectin

Mor

talit

y (%

)M

orta

lity

(%)

Dose (ng/insect)

1 3 2

132

9998

95

90

80706050403020

98

95

90

80

7060504030

20

0.1 1.0 10.0

0,01 0,10 1,00 10,00

esfenvalerate, from 1.8 to 11.5 for lambda-cyhalothrin, andfrom 1.9 to 5.5 for mevinphos. Later, Salazar & Araya (2001)found higher RRs values for the same insecticides in otherpopulations of T. absoluta.

Resistance to abamectin, cartap, methamidophos andpermethrin was reported in several Brazilian populations ofT. absoluta (Siqueira et al. 2000). The RRs values varied from5.2 to 9.4 for abamectin, from 2.2 to 21.9 for cartap, from 2.6 to4.2 for metamidophos, and from 1.9 to 6.6 for permethrin. Inother study, Siqueira et al. (2001) studied the toxicity ofabamectin, with and without synergists, to six abamectinresistant populations of T. absoluta. A complex result was

CASTELAR (1)ROSARIO (2)BELLA VISTA (3)

Dose ( g/insect)�


Table 2. Insecticides applied to control the ROSARIOpopulation of T. absoluta before the insects were collectedfor this study. Módulo Experimental de Nuevas Tecnologías,Rosario, Santa Fe.

Table 1. Susceptibility of Argentine populations of the tomato leafminer, T. absoluta, to insecticides.

195% CL = 95% confidence limits; 2Resistance ratio = LD50 greenhouse population/LD50 laboratory population; 3NS = No significant;4Significantly different from the laboratory-susceptible population (CASTELAR) (P < 0.05); 5Significantly different from 1 (P < 0.05).

obtained: piperonyl butoxide (an inhibitor of the mixedfunction microsomal oxidases activity —MFMO—)suppressed the abamectin resistance completely in only onepopulation and partially in the rest; triphenylphosphate (aninhibitor of the esterase activity) suppressed completely theabamectin resistance in four populations; diethyl maleate (aninhibitor of the glutathion S-transferase activity) suppressedpartially the resistance in nearly all populations. These resultssuggested to the authors that the resistance to abamectin inT. absoluta populations may be oligo or even polyfactorial,and that several genes should be involved.

In this work, the existence of insecticide resistance inArgentine populations of T. absoluta has been experimentallydemonstrated for the first time. Deltamethrin resistance wasobserved in the two populations studied (ROSARIO andBELLA VISTA), and a weak resistance to abamectin wasobserved just in one of them (BELLA VISTA).

Deltamethrin is an insecticide widely used in the HorticulturalBelt of Rosario city (where the ROSARIO population wascollected). We found a high level of resistance (> 68.4) todeltamethrin in individuals from the ROSARIO population. In75% of cases, pyrethroids (deltamethrin or lambda-cyhalothrin)were sprayed before our sampling (Table 2). The deltamethrinresistance observed could be due to the high selective pressureexerted by pyrethroids on this population.

Abamectin was introduced for tomato leafminer controlin the Horticultural Belt of Rosario city in the 1990s toovercome the decrease of cartap efficacy. The ROSARIOpopulation received no application of abamectin, neitherbefore the insects collection nor in recent previous years(Table 2). We found no significant differences between theLD50 values of this insecticide evaluated on the ROSARIO

and CASTELAR populations.Metamidophos is a broad spectrum systemic insecticide

used by the farmers in the Horticultural Belt of Rosario cityonly during the vegetative growth stage of tomato because ofits pre-harvest interval of 10 days. The lack of resistance tometamidophos in the ROSARIO population could be due tothe scarce use of this compound in the sampling site (Table 2).

Deltamethrin was ineffective to control the tomatoleafminer in the Experimental Station of Bella Vista city asresulted from efficacy assays carried out in the period 1981to 1987 (Cáceres 1992), when this pest began to compromisetomato production in this location. However, deltamethrin isused by farmers to control several tomato and pepper pestspecies (9.5% of the total number of sprays per cultivationcycle) (S. Cáceres, personal communication). The total numberof sprays received by the BELLA VISTA population before

Insecticide Population n Slope ± SE

LD50 (95% CL) 1

µg a.i./larva χ2 Resistance Ratio2

(95% CL)1

Deltamethrin CASTELAR 479 0.88 ± 0.13 0.35 (0.22 – 0.55)

3.06NS 3

--

ROSARIO 115 -- > 24.00 -- > 68.38 BELLA VISTA 130 -- > 24.00 -- > 68.38 Methamidophos CASTELAR 230 4.42 ± 0.45 0.81

(0.65 – 0.96) 2.12NS

--

ROSARIO 222 1.85 ± 0.44 0.65 (0.21 – 1.06)

1.06NS

0.79 (0.40 – 1.60)

BELLA VISTA 146 4.16 ± 0.45 0.70 (0.55 – 0.85)

0.71NS

0.86 (0.65 – 1.5)

ηg a.i./larva Abamectin CASTELAR 348 0.97 ± 0.12 0.16

(0.09 – 0.27) 4.83NS

--

ROSARIO 324 1.35 ± 0.19 0.41 (0.23 – 0.62)

0.98NS

2.48 5

(1.22 – 5.02) BELLA VISTA 188 1.43 ± 0.29 0.57 4

(0.28 – 0.92) 1.47NS

3.49 5

(1.64 – 7.42)

Months (year 2000) Insecticide

Number ofapplications

Commercial name

June to October

Deltamethrin 7 Decis 5

July to November

Lamdba-cyhalotrin

5 Karate

July Methamidophos 1 TamaronAugust Cartap 1 Padam 50 SPSeptember and October

Imidacloprid 2 Confidor


Table 3. Insecticides applied to control the BELLA VISTApopulation of T. absoluta before the insects were collectedfor this study. Experimental Station, INTA, Bella Vista,Corrientes.

the insect collection was 11, with seven applications ofabamectin (63.6%), three of imidacloprid (27.3%) and one ofdeltamethrin (9%) (Table 3). During the two previous years,deltamethrin was not used in the greenhouse where thispopulation was collected, but it was applied in othergreenhouses of the same Experimental Station.

In the BELLA VISTA population, a high deltamethrinresistance (RR > 68.4) was observed, although this populationreceived a relatively low number of pyrethroids applications.This result is more difficult to explain. Deltamethrin was usedin other greenhouses in the Horticultural Belt of Bella Vista,so resistance could be due to migration. An incipientabamectin resistance was observed in BELLA VISTA (seebelow), so an alternative explanation is that deltamethrinresistance is due to cross-resistance after abamectin selectivepressure. Pyrethroids and abamectin have different sites ofaction, however, a common metabolic detoxificationmechanism could confer resistance to both insecticidegroups. For instance, abamectin resistance in the Coloradopotato beetle, Leptinotarsa decemlineata (Say), largelyresulted from increased MFMO activity (Clark et al. 1994).The involvement of MFMO in the resistance to deltamethrinwas also confirmed in Cidia pomonella (L.) after in vitrometabolism studies (Sauphanor et al. 1997). Abro et al. (1988)reported a cypermethrin resistant population of Plutellaxylostella (L.) which was also resistant to abamectin,indicating that cross-resistance between pyretroids and thelatter is possible. The simultaneous application of piperonylbutoxide was followed by partial reversion of the resistanceto deltamethrin in C. pomonella (Sauphanor et al. 1997).Piperonyl butoxide also synergized abamectin in resistantindividuals of P. xylostella (Abro et al. 1988) and, as discussedabove, T. absoluta (Siqueira et al. 2001). These results suggestthat MFMO activity could be a mechanism of resistance toboth pyrethroids and abamectin.

Abamectin, in combination with mineral oil, wasintroduced for chemical control of the tomato leafminer inBella Vista in 1994 and it is still effective in the field (Cáceres2000). Abamectin has been used in the greenhouses of theExperimental Station of Bella Vista before collecting theBELLA VISTA population and during the last two years, anda weak resistance to this compound (RR = 3.5) was observed.It is possible that resistance is arising due to the selectivepressure exerted by the application of abamectin. Otherpossibility is that the values observed are due to naturalvariation (this can not be confirmed because in Argentina

there is not a baseline of insecticide toxicity to T. absoluta).Methamidophos was not used for chemical control of the

tomato leafminer in the Bella Vista Experimental Station, mainlydue to the relatively low efficacy of this compound incomparison with abamectin (Cáceres 1992). Nevertheless,metamidophos is used by growers to control several tomatoand pepper pest species (26.2% of the total number of spraysper cultivation cycle on tomato and pepper) (S. Cáceres,personal communication). The lack of usage in the samplingsite would explain that no resistance was observed for thiscompound in the BELLA VISTA population (Table 3).

In the Litoral Region of Argentina, protected tomatoproduction offers a favorable environment for thedevelopment of T. absoluta from May to August, providingit with food and shelter. Moreover, since populations developfaster in greenhouses than outdoors, the population leveland the consequent damage abruptly increase since earlyOctober, which leads to early use of insecticides underprotected cultivation. The tomato leafminer has severalbiological traits that favor resistance development. It hasmany generations per year (more than five), which overlap inprotected crops, it has a relatively high fecundity (an averageof 40 to 55 eggs per female) and it survives in the soil at thepupa stage (Botto 2000). The larvae and pupae are transportedform one region to another in infested containers and fruits,allowing the mixing of individuals subjected to differentchemical regimens.

Although a rotation of different active ingredients wasdone during each cultivation cycle in the two populationsstudied, it was not aimed to manage resistance. The lack ofinsecticide resistance management tactics favors resistancedevelopment. The occurrence of resistant individuals undergreenhouses constitutes a potential danger. Taking intoaccount that the sides of the greenhouses are lifted wheneverrequired, for regulating the temperature inside them, theresistant individuals might migrate outdoors in spring,colonizing outdoor tomato crops. When insecticides areapplied, the resistant individuals have a biological advantagein contrast with susceptible ones. This would contribute tothe development of resistance in outdoor tomato crops.

Resistance development is a consequence of insecticideapplications on an insect population and it must bemanaged. Resistance management should be a componentof integrated pest management, which seeks to minimizepesticide usage through the application of alternativetactics such as cultural control and conservation of naturalcontrol through selective insecticides. Monitoring thesusceptibility of different populations exposed to distinctactive ingredients is essential. The data obtained by meansof a monitoring plan should be used to design resistancemanaging strategies, for example, the alternation ofinsecticides with different modes of action anddetoxification, or the diminishing of conventional insecticideuse by employing alternative control tools. Several pests,such as thrips and white flies, develop on tomato crops andare sometimes controlled by the same compounds usedagainst the tomato leafminer. For this reason, insecticideresistance management of T. absoluta should be consideredin the context of key-pest arthropod complexes of crops.

Month (year 2000) Insecticide

Number ofapplications

Commercialname

April Deltamethrin 1 Decis 5 May to September

Abamectin 7 Vertimec

July to September

Imidacloprid 3 Confidor


Acknowledgments

To the Centro de Investigaciones de Plagas e Insecticidasfor providing the technical grade insecticides deltamethrinand abamectin. To Bayer Argentina for donating the technicalgrade insecticide metamidophos. To Ing. Agr. Sara Cáceres(E.E.A.INTA Bella Vista) for sending the T. absolutapopulation from Bella Vista. To the two anonymous reviewersfor their helpful comments.

Literature Cited

Abro, G.H., R.A. Dybas, S.J. Green & D.J. Wright. 1988.Toxicity of avermectin B1 against a susceptible laboratorystrain and an insecticide-resistant strain of Plutellaxylostella (Lepidoptera: Plutellidae). J. Econ. Entomol.81: 1575-1580.

Bahamondes, L.A. & A.R. Mallea. 1969. Biología enMendoza de Scrobipalpuloides absoluta (Meyrick)Povolny (Lepidoptera – Gelechiidae), especie nueva parala República Argentina. Rev. FCA UNCuyo (Argentina)XV: 96-104.

Benavent, J., E. Kueffner & A. Vigiani. 1978. Organizacióny planificación de la investigación para el desarrollo deun programa de control integrado de la polilla del tomateScrobipalpula absoluta (Meyrick), Lepidoptera:Gelechiidae, en la República Argentina. Curso dePerfeccionamiento en Control Integrado de Plagas.Compendio, Tomo II. Buenos Aires, INTA, 16p.

Botto, E.N., S.A. Ceriani, S.N. López, E.D. Sani, G. Segade,C. Cédola & M.M. Viscarret. 2000. Control biológicode plagas en cultivos protegidos en la Argentina.Posibilidades para su utilización. Rev. Investigac. INTA,RIA 29: 83-99.

Cáceres, S. 1992. La polilla del tomate en Corrientes. Biologíay control. Estación Experimental Agropecuaria Bella Vista,INTA, 19p.

Cáceres, S. 2000. La polilla del tomate: Manejo químico-cultural. Hoja de Divulgación 15. Estación ExperimentalAgropecuaria Bella Vista, INTA, 5p.

Cámara de Sanidad Agropecuaria y Fertilizantes de laRepública Argentina. 2001. Guía de productosfitosanitarios para la República Argentina. Buenos Aires,1.597p.

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Food Agriculture Organization. 1996. Anuario Producción.Statistics Series n° 135, v. 50. 235p.

Galarza, J. & O. Larroque. 1984. Control de Scrobipalpula

absoluta (Meyr.) (Lepidoptera: Gelechidae) en tomate.IDIA 421-424: 15-18.

Gómez Riera, P. (ed.). 1992. Argentina frutihortícola ‘92.Mendoza, Asociación Argentina de Horticultura(ASAHO), 266p.

Instituto Agronómico Nacional & Agencia de CooperaciónInternacional de Japón (JICA). 1994. Control integradode la palomilla del tomate Scrobipalpula absoluta(Meyrick, 1917). Caacupé, Paraguay, JICA, 173p.

Larraín, P. 1986. Eficacia de insecticidas y frecuencia deaplicación basada en niveles poblacionales críticos deScrobipalpula absoluta (Meyrick), en tomates. Agric.Técn. 46: 329-333.

Lichtfield, J.T. & F. Wilcoxon. 1949. A simplified method ofevaluating dose-effect experiments. J. Exp. Ther. 96: 99-113.

Moore, J.E. 1983. Control of tomato leafminer (Scrobipalpulaabsoluta) in Bolivia. Trop. Pest Manag. 29: 231-238.

Polack, L.A. 1999. Ensayos de eficacia de plaguicidas empleadoscontra la polilla del tomate Tuta absoluta (Meyrick). BuenosAires, Centro Agrícola El Pato, INTA. 2p.

Riquelme, A.H. 1993. Control integrado de plagas en tomate.San Juan, Editar, 34p.

Robertson, J.L. & H.K. Preisler. 1992. Pesticide bioassayswith arthropods. Boca Ratón, CRC Press, 127p.

Salazar, E.R. & J.E. Araya. 1997. Detección de resistencia ainsecticidas en la polilla del tomate. Simiente 67: 8-22.

Salazar, E.R. & J.E. Araya. 2001. Respuesta de la polilla deltomate, Tuta absoluta (Meyrick), a insecticidas en Arica.Agric. Téc. 61: 429-435.

Sauphanor, B., A. Cuany, J.C. Bouvier, V. Brosse, M. Amichot,& J.B. Bergé. 1997. Mechanism of resistance todeltamethrin in Cydia pomonella (L.) (Lepidoptera:Tortricidae). Pest. Biochem. Physiol. 58: 109-117.

Siqueira, H.A. de, R.N. Guedes, D.B. Fragoso & L.C.Magalhães. 2001. Abamectin resistance and synergismin brazilian populations of Tuta absoluta (Meyrick)(Lepidoptera: Gelechiidae). Int. J. Pest Manag. 47: 247-251.

Siqueira, H.A. de, R.N. Guedes & M.C. Picanço. 2000.Insecticide resistance in populations of Tuta absoluta(Lepidoptera:Gelechiidae). Agric. Forest Entomol. 2: 147-153.

Souza, J.C., P.R. Reis, A. de Pádua Nacif, J.M. Gomes &L.O. Salgado. 1983. Controle da traça-do-tomateiro.Histórico, reconhecimento, biología, prejuízos e controle.


Belo Horizonte, Empresa de Pesquisa Agropecuária deMinas Gerais, 15p.

Stoppani, M.I. & J.P. Rodríguez. 1992. El tomate(Lycopersicon esculentum Mill.) y su cultivo bajo

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Received 07/X/04. Accepted 07/X/04.

65Efecto del imidacloprid en el control de la polilla del tomate (Tuta absoluta Meyrick)Volumen 26, Nº 1, Páginas 65-72IDESIA (Chile) Enero - Abril 2008

1 Cátedra de Zoología Agrícola, Facultad de Agronomía, Universidad de Buenos Aires. Av. San Martín 4453, Buenos Aires (CP C1417DSE), Argentina. E-mail: [email protected]

2 Cátedra de Terapéutica Vegetal, Facultad de Agronomía, Universidad de Buenos Aires. Ídem anterior. E-mail: [email protected]

Fecha de Recepción: 06 Marzo 2006Fecha de Aceptación: 22 Octubre 2007

EFECTO DEL IMIDACLOPRID EN EL CONTROL DE LA POLILLA DEL TOMATE (TUTA ABSOLUTA MEYRICK)

EFFICACY OF IMIDACLOPRID TO CONTROL THE TOMATO BORER (TUTA ABSOLUTA MEYRICK)

Marcelo Dante Collavino1; Rosana Alejandra Giménez2

RESUMEN

La grave incidencia de Tuta absoluta en la producción de tomate, el alto uso de plaguicidas para su control, el riesgo de contami-nación del ambiente y la generación de resistencia hacen que sea muy importante encontrar formas alternativas de control eficiente de esta plaga. Con el fin de evaluar la eficacia del imidacloprid en el control de la polilla del tomate, en distintas dosis y formas de aplicación se desarrolló este ensayo en condiciones de invernáculo.Para ello se prepararon dos diluciones del insecticida, que fueron aplicadas de dos formas: por riego y por inmersión de la raíz del plantín con su pan de tierra.Para evaluar el daño se realizó el cálculo del porcentaje de folíolos dañados por planta y el número de lesiones por hoja en dis-tintos momentos desde la aplicación. El diseño fue factorial, completamente aleatorizado y con nueve repeticiones, aplicándose ANOVA. Se comprobó que hay diferencias significativas entre las diluciones y también entre las dos formas de aplicación (riego e inmersión). Siendo los tratamientos que mejor controlaron a la plaga: dilución al 3,5% aplicada por riego y dilución al 7% aplicada por inmersión. Palabras clave: Tuta absoluta, imidacloprid, riego, inmersión.

ABSTRACT

The incidence of Tuta absoluta in tomato production, the use of pesticides for its control, the risk of contamination to the envi-ronment and the creation of a generation of resistance, makes it very important to find alternative ways to efficiently control the tomato borer. This test was developed under greenhouse conditions to assess the effectiveness of the imidacloprid to the control of this pest at different rates and application forms. Two dilutions of the insecticide were prepared and applied in two different ways: by watering and by the immersion of the root of the plants into the soil bed. To evaluate the damage, calculations were carried out on the percentage of the leaves damaged on each plant and on the number of lesions on each leaf at different moments of the application. The design was factorial, completely randomized and with 9 replications, and an ANOVA was carried out. Significant differences were confirmed among the dilutions and also among the two application forms (watering and immersion). The better treatments were: dilution of 3,5% applied by watering and dilution of 7% applied by immersion. Key words: Tuta absoluta, imidacloprid, watering, immersion.

INTRODUCCIÓN

En el cultivo de tomate el tipo de producción más tecnificado es el realizado bajo invernáculo, donde el problema de la polilla del tomate (T. absoluta) es mucho más grave que a campo (Ripa, 1981).

Dentro del invernáculo es menor la incidencia de las bajas temperaturas, produciéndose condiciones muy favorables para incrementar la incidencia de esta plaga, que acorta su ciclo de vida y produce muchas generaciones superpuestas a lo largo del ciclo de cultivo.

IDESIA (Chile) Volumen 26, Nº 1, Enero-Abril, 200866

T. absoluta (Lepidoptera; Gelechiidae) pro-duce daños muy importantes al cultivo del tomate en casi todas las zonas de producción hortícola de Argentina (INTA, 1991). Las larvas lesionan el follaje haciendo galerías dentro de las hojas que pueden llegar a ocupar gran parte del área foliar. También penetran en el fruto construyendo túneles que al llenarse de excrementos causan la pudrición y caída de los mismos (Betancourt, 1995). De esta manera se pierde rendimiento y también disminuye la calidad de los frutos obtenidos.

Los graves daños que esta plaga produce han hecho que los productores aplicaran insecticidas muy frecuentemente, generando resistencia a la mayoría de los insecticidas utilizados, especialmente hacia los fosforados (Larraín, 1986). En Argentina, actualmente, están registrados numerosos productos para el control de esta plaga: ciflutrina, ciperme-trina, deltametrina, fenvalerato, lambdacihalotrina y permetrina (piretroides), acefato, clorpirifós, fenitrotión, metamidofós, piridafentión y triazofós (organofosforados), abamectín y cartap (microbio-lógicos), clorfluazurón, lufenurón, metoxifenocide, tebufenozide, teflubenzurón y triflumurón (IGR), spinosad (Naturalyte) y tiociclán hidrogenoxalato (nereistoxina) (CASAFE, 2001). Mientras que el imidacloprid se encuentra registrado para aplicar en el cultivo de tomate exclusivamente para controlar moscas blancas (Bemisia tabaci, Trialeurodes spp. y Aleurothripsus spp.) y minador del tomate (Faustinus cubae) y trips (Frankliniella schultzei).

Otros investigadores han realizado estudios para establecer la eficacia de insecticidas (Reis et al., 1998; Lima y Machado, 1996) en aplicaciones foliares para controlar T. absoluta.

El imidacloprid se caracteriza por tener un modo de acción sistémico y de contacto, amplio espectro de acción y posibilidad de ser absorbido tanto por follaje como por raíces. Además, posee un mecanismo de acción diferente al de la mayoría de los insecticidas, por lo que no se han registrado casos de resistencia en las plagas. Pertenece al grupo de las nitroguanidinas y posee un efecto residual de varias semanas y una baja toxicidad para mamíferos, con una dosis letal media (DL 50) oral aguda en rata 24 h de 450 mg/kg (CASAFE, 2001). Además, Epperlein et al. (1997) mostraron que este insecticida aplicado al suelo no produjo efectos adversos sobre artrópodos predadores de la superficie del suelo.

Todas estas características hacen que sea posible su aplicación mediante métodos no convenciona-les, haciendo tratamientos menos contaminantes y más económicos, como serían las aplicaciones localizadas, evitando la pulverización foliar en cobertura total.

Así, con el fin de encontrar formas alternativas de control eficiente de la polilla del tomate, evalua-mos la aplicación de imidacloprid mediante riego y por inmersión de raíces al trasplante.

MATERIALES Y MÉTODOS

El insecticida con que se realizó este trabajo es el formulado comercial Confidor SL100 ® de Bayer, cuyo ingrediente activo es el imidacloprid.

El cultivo fue realizado en un invernáculo de esta Facultad, con tomate “platense común” y ejemplares de T. absoluta criados en cámaras.

La cría de T. absoluta se realizó en jaulas con luz artificial, sobre plantines de tomate cultivados en macetas plásticas.

La siembra de tomate fue realizada en almá-cigos tipo speedling, con sustrato previamente desinfectado con sulfato neutro de oxiquinoleina. Estos almácigos se regaron periódicamente con solución fertilizante N-P-K (15-15-15).

Se utilizaron 45 macetas plásticas de 25 cm de diámetro, para realizar allí el trasplante de los plantines.

Se prepararon dos diluciones del insecticida, una al 3,5% y otra al 7%. Ambas fueron aplicadas de dos formas distintas:1) Riego de las macetas con regadera, un día antes

del trasplante. El riego se realizó hasta saturar el suelo.

2) Inmersión de la raíz del plantín con su pan de tierra, durante 10 seg. Una vez escurrida, el plantín se trasplantaba a la maceta.Quedan así determinados cinco tratamientos:

– Testigo (sin insecticida); – Dilución al 3,5% aplicada por inmersión;– Dilución al 3,5% aplicada por riego;– Dilución al 7% aplicada por inmersión; – Dilución al 7% aplicada por riego.

Luego de realizar la conducción y la poda de los brotes axilares de las plantas, se liberaron en el interior del invernáculo aproximadamente 100 ejemplares de T. absoluta (adultos y pupas), tapan-

67Efecto del imidacloprid en el control de la polilla del tomate (Tuta absoluta Meyrick)

do con tul y papel todos las aberturas por donde pudieran escapar las polillas.

Para evaluar el daño se realizó el cálculo del porcentaje de folíolos dañados por planta y el número de lesiones por hoja, a los 27, 34, 41 y 48 días desde la aplicación del producto.

Se implementó un diseño estadístico factorial con un tratamiento adicional, completamente aleatorio y con nueve repeticiones por tratamiento; luego los datos fueron analizados por medio de análisis de variancia –ANOVA– al 5 y 1 %.

RESULTADOS Y DISCUSIÓN

Como consecuencia de la aplicación del imi-dacloprid se advierte, en primera instancia, que las plantas tratadas no sufren el ataque de la polilla, o lo sufren en menor medida que aquellas a las cuales no se les aplicó dicho insecticida.

A continuación se presentan los datos generados en las observaciones semanales realizadas.

Como puede observarse en la Figura 1, el por-centaje de folíolos dañados por planta se incrementa

Tabla 1

Promedios registrados a 27 días de la aplicación

Testigo 3,5% riego 3,5% inmersión 7% riego 7% inmersión

Porcentaje de folíolos dañados por planta

34,88 4,13 16,48 0,00 2,89

Número de lesiones por hoja 3,95 0,49 2,25 0,00 0,24

Tabla 2




44,60 10,44 26,75 3,20 11,26


Tabla 3




55,47 29,66 45,00 10,40 26,33


Tabla 4




63,48 31,01 48,43 13,47 28,68



a lo largo del tiempo. Los distintos tratamientos se diferencian del testigo en mayor o menor medida y en todos ellos se evidencia un daño de menor magnitud que en éste.

En la Figura 2 se observa que a los 34 días de la aplicación hay 3 tratamientos con daños que permanecen por debajo del umbral de daño económico (UDE) sugerido por Ariso (1997), quien considera que para realizar una aplicación de insecticida en tomate cultivado en invernáculo se deben observar en promedio 3 lesiones por hoja. Así, en este ensayo (Figura 2) los tratamientos realizados alcanzaron este umbral de daño en dis-tintos períodos desde la aplicación: el testigo en la primera observación (27 días) ya había superado el umbral mencionado; en los tratamientos 3,5% inmersión, 7% inmersión, 3,5% riego alcanza el

mismo a los 28, 35 y 37 días, respectivamente, mientras que el tratamiento 7% riego no alcanzó este UDE; sin embargo, en este último tratamiento, no se puede considerar que fue un largo período de protección de las plantas, ya que se produjo fitotoxicidad en el tomate.

Con análisis estadístico se verificó la existencia de diferencias altamente significativas entre ambas diluciones y también entre las dos formas de aplica-ción (riego e inmersión) tanto para los resultados de lesiones por hoja (Tablas 5 a 8) como para porcentaje de folíolos dañados (Tablas 9 a 12).

No existe interacción AB; Diferencias altamente significativas entre diluciones; Diferencias altamente significativas entre aplicaciones.

La dilución al 7% aplicada por riego se descartó del análisis por haber producido en todas las plantas

0

10

20

30

40

50

60

70

27 días 34 días 41 días 48 días

Días desde la aplicación

Porc

enta

je d

e fo

líolo

s da

ñado

s


Figura 1. Evolución del daño.

Tabla 5

ANOVA. Lesiones por hoja a los 27 días de la aplicación.

Fuentes de Variación

SC GL CM F F 0.05 F 0,01

Dilución 137.181 2 68.591 42.332 ** 3.185 5.070

Aplicación 9.019 1 9.019 5.567 * 4.035 7.180

Interacción AB 5.266 1 5.266 3.250 4.035 7.180

Error 79.394 49 1.620

Total 230.861 53 4.356

No existe interacción AB; Diferencias altamente significativas entre diluciones; Diferencias significativas entre aplicaciones.


0

3

6

9

12

15

27 días 34 días 41 días 48 días

Días desde la aplicación

Les

ione

s po

r ho

ja

3,5% riego 3,5% inmersiónTestigo 7% riego 7% inmersión

Figura 2. Lesiones por hoja a través del tiempo.

Tabla 6

ANOVA. Lesiones por hoja a los 34 días de la aplicación


SC GL CM F F 0,05 F 0,01

Dilución 431.402 2 215.701 50.353 ** 3.185 5.070

Aplicación 70.492 1 70.492 16.456 ** 4.035 7.180

Interacción AB 5.397 1 5.397 1.260 4.035 7.180

Error 209.904 49 4.284

Total 717.195 53 13.532


Tabla 7



SC GL CM F F 0,05 F 0,01

Dilución 559.424 2 279.712 51.202 ** 3.185 5.070

Aplicación 197.589 1 197.589 36.169 ** 4.035 7.180

Interacción AB 0.902 1 0.902 0.165 4.035 7.180

Error 267.681 49 5.463

Total 1025.597 53 19.351



Tabla 8



SC GL CM F F 0,05 F 0,01

Dilución 824.602 2 412.301 21.110 ** 3.185 5.070

Aplicación 297.374 1 297.374 15.225 ** 4.035 7.180

Interacción AB 0.421 1 0.421 0.022 4.035 7.180

Error 957.043 49 19.531

Total 2079.440 53 39.235


Tabla 9

ANOVA. Porcentaje de folíolos dañados a los 27 días de la aplicación


SC GL CM F F 0,05 F 0,01

Dilución 10789.821 2 5394.911 28.533 ** 3.185 5.070

Aplicación 529.786 1 529.786 2.802 4.035 7.180

Interacción AB 205.504 1 205.504 1.087 4.035 7.180

Error 9264.782 49 189.077

Total 20789.893 53 392.262

No existe interacción AB; Diferencias altamente significativas entre diluciones; No hay diferencias entre aplicaciones.

Tabla 10



SC GL CM F F 0,05 F 0,01

Dilución 13211.075 2 6605.537 36.066 ** 3.185 5.070

Aplicación 1337.561 1 1337.561 7.303 ** 4.035 7.180

Interacción AB 153.031 1 153.031 0.836 4.035 7.180

Error 8974.321 49 183.149

Total 23675.986 53 446.717



Tabla 11

ANOVA Porcentaje de folíolos dañados a los 41 días de la aplicación


SC GL CM F F 0,05 F 0,01

Dilución 12391.490 2 6195.745 35.632 ** 3.185 5.070

Aplicación 2199.270 1 2199.270 12.648 ** 4.035 7.180

Interacción AB 0.811 1 0.811 0.005 4.035 7.180

Error 3520.291 49 173.883

Total 2311.862 53 436.073

Tabla 12



SC GL CM F F 0,05 F 0,01

Dilución 16266.865 2 8133.433 49.073 ** 3.185 5.070

Aplicación 2396.430 1 2396.430 14.459 ** 4.035 7.180

Interacción AB 11.001 1 11.001 0.066 4.035 7.180

Error 8121.290 49 165.741

Total 26795.586 53 505.577


tratadas una marcada disminución del crecimiento y pérdida de hojas.

Los tratamientos que mejor controlaron a la plaga fueron (figura 1):– Dilución al 3,5 % aplicada por riego.– Dilución al 7% aplicada por inmersión.

Como se aprecia en la Figura 2, la aplicación por inmersión de la dilución al 7% presentó niveles de daño inferiores al UDE hasta los 37 días después del tratamiento y la aplicación por riego de la dilución al 3% hasta los 35 días.

A través de un ensayo, bajo condiciones de invernáculo, no se puede establecer con certeza cuál es el tratamiento adecuado para controlar la polilla del tomate en condiciones de campo, ya que los resultados tienen sustento sólo en este ámbito de producción.

Finalmente, en cultivos protegidos de tomate, teniendo en cuenta aspectos económicos del con-trol de plagas, sería recomendable la aplicación de imidacloprid a la raíz de las plantas jóvenes por inmersión (al 7% en agua) durante el transplante, ya que es el tratamiento que requiere en total una menor cantidad de producto y tiene una alta eficacia de control.

CONCLUSIONES

En condiciones de invernáculo la aplicación de la dilución al 7% aplicada mediante riego resultó fitotóxica para el tomate platense común.

Las aplicaciones de la dilución al 3,5% apli-cada por riego y de la dilución al 7% aplicada por inmersión resultaron ser las más adecuadas para el control de la plaga, por su eficacia y periodo post-tratamiento con daños menores al UDE.


LITERATURA CITADA

ARISO, E. (1997). Comunicación personal, Departamento Técnico de Bayer.

BETANCOURT, C. M. y SCATONI I. B. (1995). Description of the development stages of the “tomato borer”, Scrobipalpuloides absoluta (Mayrick) (Lep., Gelechiidae). Boletín de investigación, Facultad de Agronomía, Universidad de la República. 1995, 45: 1-14. Uruguay.

CASAFE (Cámara de Sanidad Agropecuaria y Fertilizantes). (2001). Guía de productos fitosanitarios para la República Argentina.1368 pp. CASAFE, Buenos Aires, Argentina.

EPPERLEIN, K.; SCHMIDT, H. W.; SCHWALBE, R. 1997. Influence of Gaucho R used as seed treatment of maize on the infestation with viruses, pests and on the epedaphic soil fauna. Archives of the Phytopatology and Plant Protection, 31 (2): 185-200. Germany.

INTA Centro Regional Cuyo (1991). “Manual de cultivo de tomate”. INTA, Argentina.

LARRAÍN, P. (1986). Eficacia de insecticidas y frecuencia de aplicación en S. absoluta. Avicultura Técnica Nº 46, Chile.

LIMA, J. O. G. de; MACHADO, W. A. 1996. Greenhouse evaluation of insecticides for control of the tomato leafminer Scrobipalpuloides absoluta (Meyrick). Revista Ceres. 48 (248): 337-345, Brazil.

REIS, P. R.; SOUZA, J. C. de; DE SOUZA, J. C. 1998. Chemical control of Tuta absoluta (Meyrick) in staked tomato plants. Ciencia e Agrotecnologia, 22 (1): 13-21. Brazil.

RIPA, R. (1981). “Avances en el control de la polilla del tomate”. Agricultura Técnica Nº 41, Chile.

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