Bioecology and management of diamondback moth in India

Bioecology in India

and Management Diamondback

7

Moth

S. Chelliah and K. Srinivasan Department of Agricultural Entomology, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu 641003, India. ‘Division of Entomology, Indian Institute of Horticultural Research, Bangalore 560080, India

Abstract

In India, the diamondback moth, Plutella xylostella (L) infests cabbage, cauliflower, radish, knol khol, turnip, beetroot, mustard, and amaranthus. Cauliflower and cabbage are the most preferred hosts. Eggs are minute, whitish yellow, and incubation lasts for three to four days. There are four larval instars and the total larval period including prepupal stage extends for 10 days in the hot and rainy seasons and 12 to 15 days in the cold season. The larva pupates in a silken cocoon and pupal period ranges from four days in the hot and rainy seasons and from four to five days in the cold season. Adult longevity lasts for 6 to 13 days. Moths lay eggs in depressions on the leaf along the midrib and larger veins. Eggs are laid on the day of emergence soon after mating. Thirteen to fourteen generations have been observed in a year in the southern part of India. Apanteles plutellae is the dominant larval parasitoid. It is widespread in distribution and parasitizes up to 72% of the larvae. The major mortality factors recorded through life table studies are parasitization due to A. plutellae throughout the larval stage, predatory ants, birds, spiders, and rainfall in 1st and 2nd larval stages. The presence of 10 3rd or 4th instar larvae up to one month after planting, or 20 medium sized larvaelplant between one and two months after planting, is identified as the economic threshold. Effective control of the pest is achieved by synthetic pyrethroids such as permethrin or fenvalerate at 75 g Al/ha. Spraying with Dipel (0.5 kg product/ha) is also effective against the larvae. Planting tomato 30 days earlier than cabbage in an inter-cropping pattern reduces the larval damage significantly. A strategy to manage the diamondback moth utilizing the threshold, selective insecticide application, suitable cropping pattern, and natural enemies is discussed.

lntroduct ion

Diamondback moth (DBM), Plutella xylostella (L) (Lepidoptera: Yponomeutidae), is an important pest of cruciferous crops and enjoys worldwide distribution (CIE 1967). Hardy (1938) stated that the pest could breed and develop between 10°C and 40°C and that the adults were active at up to 50°C. Young pupae and the adults survived for several months and the eggs and pupae for two and six weeks, respectively, at 0°C. In India, DBM was first recorded in 1914 (Fletcher 1914) on cruciferous vegetables and a perusal of literature reveals that this species is distributed all over India wherever crucifers are grown. It is one of the more thoroughly studied pests in India.

Host Range

DBM in India infests important crucifers viz: cabbage, cauliflower, radish, khol rabi (knol khol), turnip, beetroot, mustard, Brassica campestris var toria, and B.

64 Chelliah and Srinivasan

campestris var sarson (Chand and Choudhary 1977, Dube and Chand 1977, Jayarathnam 1977; Singh and Singh 1982). Non-cruciferous crop like Amaranthus virdis L has also been reported to be the host of this species (Vishakantaiah and Visweswara Gowda 1975).

Studies on the food plant preference of DBM have revealed that among several crucifers, the pest exhibits a marked preference for cauliflower and cabbage. This is probably due to the fact that both plants possess fleshy and succulent leaves compared to rest of the crucifers tested, and this probably provides olfactory and gustatory stimuli for successful host selection and development (Chand and Choudhary 1977, Dube and Chand 1977, Singh and Singh 1982).

Life History

The biology of this pest has been studied in the laboratory (Patil and Pokharkar 1971, Jayarathnam 1977) and under natural conditions in relation to ecological factors (Abraham and Padmanabhan 1968, Jayarathnam 1977).

Egg stage

Eggs are minute, whitish yellow, 0.5 mm in size. The incubation period ranges from three to six days (Abraham and Padmanabhan 1968). Patil and Pokharkar (1971) report an incubation period of four to six days under laboratory conditions. Jayarathnam (1977) records an incubation period of three to four days under both laboratory and field conditions.

Larval stage

Newly hatched larvae are pale white with a pale brown head while the fully grown caterpillars are light green, measuring 10 mm in length. The 1st instar larvae mine into the leaf. Total larval period extends from 14 to 21 days (Abraham and Padmanabhan 1968). Patil and Pokharkar (1971) observed five larval instars and a larval period of up to 11 days. However, Jayarathnam (1977) reported that there were only four instars. The 1st instar occupied three days in the hot season, 3 to 4 days in the rainy season and 4 to 5 days in the cold season. The larvae generally stay in the mines for about two days. The 2nd instar stage extends for two days in the hot and rainy seasons and 2 to 3 days in the cold season. The 3rd instar larvae generally feed on mature leaves for two days in the hot and rainy seasons and for two to three days in the cold season. The 4th instar larvae, excluding the prepupal period, consume the largest quantity of leaf tissue and last for two days in the hot season, two to three days in the rainy, and three to four days in cold season. The pre-pupal period lasts for one day in all three seasons. The total larval and prepupal period are estimated as 10 days in the hot and rainy seasons and 12 to 15 days in the cold season.

Pupal stage

Pupation takes place in a loose mesh of silken cocoon spun by the caterpillar. The mature pupae are 6 mm long and of light brown colour. The pupal stage ranges from 7 to 1 1 days (Abraham and Padmanabhan 1968). However, Patil and Pokharkar (1971) report the pupal period to vary from three to seven days, with an average of five days. Jayarathnam (1977) report the pupal period to last up to four days in the hot and rainy seasons and four to five days in the cold season. These results show significant variation in pupal period in different parts of India, possibly due to climatic variations.

Ecology and Management of DBM in India 65

Adult

Adults are grey moths with a wing expanse of 14 mm. Their longevity ranges from 3 to 11 days (Abraham and Padmanabhan 1968). Patil and Pokharkar (1971) report the lifespan of male and female to be 10.4 and 12.1 days respectively. Jayarathnam (1977) found adults to survive for three to six days without food and for 1 1 to 16 days provided with food. Adults were found to emerge during the evening and rarely in the morning hours.

Mating, oviposition, and fecundity

The moths mate at dusk on the day of emergence. Oviposition begins in the evening and lasts up to 7 pm; during the rest of the night, the moths are not active (Jayarathnam 1977). Jayarathnam further observes that the individuals in a copulating pair face op- posite directions and hang downwards with the female above. Mating lasts one to two hours and females mate only once. Typically, eggs are laid in depressions on the leaf along the midrib and larger veins or on concave surfaces near smaller veins. On average, 63.4% eggs are laid on the upper leaf surface. Most females (90%) lay eggs on the same day of emergence. The oviposition period extends to 10 days with peak oviposition occur- ring on the day of emergence. Patil and Pokharkar (1971) report that the fecundity ranges from 71 to 203 eggs/female. Atwal (1955) investigated the factors influencing fecundity and reports that females reared at low temperatures (7 to 24°C) laid more eggs than those reared at higher temperatures (28 to 35°C). The fecundity of adults increased when exposed to increased photoperiod.

Number of generations

Jayarathnam (1977) observed that DBM completed 13 to 14 generations per year in Bangalore, India. He also postulated that if the eggs were to be laid by the adults of each generation on the same day as emergence, up to 16 generations per year could be completed.

Natural Enemies

Parasitoids

In Coimbatore, Tamil Nadu, Cherian and Basheer (1938) observed 59.9% parasitization by Brachymeria excarinata Gahan and 18.2% parasitization due to Tetrastichus sokolowskii Kurdj. Simmonds and Rao (1960) reported Voria ruralis (Fall) and an Angitia (Horogenes) sp from Srinagar, Jammu and Kashmir. Thyraeella collaris Grav and Macromalon orientale Kerrich were recorded as larval parasitoids in Shillong, Meghalaya (Chacko 1968). Patel and Patel (1968) reported Apanteles sp. (glomeratus group), Chelonus sp (possibly C. versatilis (Walker)), Hockeria tetraceitarsis Gram, Th. collaris, and M. orientale, the latter being the dominant larval parasitoid at Anand, Gu- jarat. Manjunath (1972) found that Trichogrammatoidea armigera Nag could be suc- cessfully reared on DBM eggs but it is not known if it would attack eggs of this pest in the field. Yadav et al (1975) studied the seasonal activity of A . plutellae at Anand. They also reported that this parasitoid appeared along with the pest in the last week of July and that the highest parasitization of 71.7% occurred in the first week of September. Heavy rains received during the last week of September reduced populations of both the pest and the parasitoid. In Bangalore, Karnataka State, Jayarathnam (1977)

66 Chelliah and Srinivasan

records A . plutellae and T. sokolowskii causing 16 to 52% mortality and 28 to 96% parasitization of 2nd instar DBM larvae. Nagarketti and Jayanth (1982) subsequently confirmed the occurrence of both the parasitoids at Bangalore. They also observed A . plutellae as the dominant larval parasitoid and T. sokolowskii to occur at low levels. They inferred from seasonal incidence studies that a clear density-dependent relationship existed between A . plutellae and the host. During their study, a large number of secondary hymenopterous hyperparasites were also recorded. They were: Anastatus sp (Eupelmidae), Aohanogmus fijiensis Ferriere (Ceraphronidae), Brachymeria excarinata Gahan (Chalcididae), Diaglyptidea sp (Ichneumonidae), Eurytoma sp (Eurytomidae), Hockeria atra Masi (Chalcididae), Pediobius imbreus (Walker) (Eulophidae), Pteromalus sp (Pteromalidae), Tetrastichus sokolowskii (Eulophidae), Tetrastichus sp (miser group) (Eulophidae). B. excarinata and T. sokolowskii acted as facultative hyperparasites. The hyperparasites, according to their study, appeared from August to October with a low (3.13%) parasitism in October and a high parasitism (39.13%) in September, the latter coinciding with peak parasitism by A . plutellae on the primary host.

Predators

Yellow wagtails (Motacilla flava) were found to feed on DBM larvae in Bangalore during cold season (Jayarathnam 1977). Jayarathnam further observed that the ants, Tapinoma melanocephalum, Pheidole spp and Camponotus sericeus were carrying away DBM larvae in the field.

Pathogen

During a two-year study on the population dynamics of major pests of cabbage and of their natural enemies in Bangalore, Nagarkatti and Jayanth (1982) collected two diseased larvae affected by nuclear polyhedrosis virus. Incidence of diseases appears to be very low and to our knowledge natural epizootics have not been reported from India.

Natural Mortality Factors

Jayarathnam (1977) studied the population dynamics of the pest by preparing life tables for 10 generations (five in rainy season and five in cold season). Major mortality factors were parasitization by A . plutellae in the larval period, predatory ants, birds and spiders in the 1st and 2nd larval instars, and rainfall in the 1st and 2nd larval instars (Tables 1 and 2). The major mortality factor at the pupal stage was parasitization by T. sokolowskii. Parasitization by T. sokolowskii was identified as the key mortality factor throughout all 10 generations. Infestation by the cabbage webworm, Hellula undalis Zell, resulted in considerable reduction of oviposition sites for DBM.

Table 1. Major mortality factors of DBM during the rainy season (July-0ctober)ª Stage Mortality factors Mortality (%)

Egg 1st larval instar

2nd larval instar

3rd larval instar Pupa Adult

infertility Rainfall (39 mm)

Predators: ants and spiders A. plutellae

Predators: ants and spiders T. sokolowskii T. sokolowskii

Sex: 45% female

6.6 11.0 59.3 52.0 13.9 4.0

32.0 9.2

ªSource Jayarathnam 1977


Table 2. Major mortality factors of DBM during the winter season (November-February)ª

Stage Mortality factors Mortality (%)

Egg Infertility 14.3 1st larval instar 60.0 2nd larval instar A. plutellae 20.0

59.2 3rd larval instar T. sokolowskii 8.0 Pupa T. sokolowskii 72.0 Adult Sex: 41% female 18.0

Predators: ants, birds, and spiders, heavy dew

Predators: ants, birds, and spiders

a Source: Jayarathnam 1977.

Seasonal Incidence

Seasonal incidence of DBM on cabbage has been studied in India at Kodaikanal, Udaipur, Anand, and Bangalore (Abraham and Padmanabhan 1968, Sachan and Srivastava 1972, Yadav et al 1975, Jayarathnam 1977, Nagarkatti and Jayanth 1982). High build-up of larval populations has been reported during February-March (late winter) and April-August (summer and mid rainy season) (Abraham and Padmanabhan 1968, Sachan and Srivastava 1972). However, Jayarathnam (1977) and Nagarkatti and Jayanth (1982) found significantly high build- ups of larval populations during the rainy season (July- September) as compared to other seasons (Figure 1).

xylostella ( D B M A. T. sokolowskii

8

‘79 ‘79 ‘80 ‘80 ‘81

Figure 1. Seasonal incidence of DBM and its natural enemies (Nagarkatti and Jayanath 1982)

Economic Thresholds

Prasad (1963) reported that seven weeks after transplanting, cabbage could sustain populations of 20 larvae/plant before significant economic injury and yield reduction

68 Chelliah and Srinviasan

were detected. Based on crop loss estimation studies conducted in Bangalore, Jayarathnam (1977) found that a population of four or more medium sized larvae (3rd or 4th instar) could render a seedling untransplantable and 10 medium sized larvae/plant up to one month after planting and 20 medium sized larvae/plant between one and two months after planting necessitated insecticide application.

Crop Loss Estimation

Krishnakumar et al (1984) estimate a 52% loss in marketable yield due to DBM attack on cabbage. Based on path coefficient analysis, the same authors estimate that DBM infestation at 55 days after planting has the maximum negative direct effect in reducing yield. DBM larval populations at 20, 30, 40, 50, and 60 days after planting and the marketable yield showed significant negative relationship for insect count taken at 40, 50 and 60 days after planting (Srinivasan 1984). The multiple linear regression equation for these larval populations in relation to loss of marketable yield was: Y =-168.79 X I +84.33 X3 21.19 -115.92 where XI , and corresponds to populations on 20, 30, 40, 50 and 60 days after planting (Srinivasan 1984).

Management

Adoption of visual damage thresholds

Successful cultivation of cabbage is hampered due to the incidence of DBM and Crocidolomia binotalis Zeller on cabbage in Bangalore (Nagarkatti and Jayanth 1982). Even though economic thresholds for both pests are on record, they are not adopted by growers who lack training or time to count and identify insects accurately. However, use of a threshold based on quick visual ratings (as revealed by the appearance of holes in leaves caused by feeding of caterpillars of both species) would require little formal training and time. After the application of a blanket spray to protect the primordia/head formation stage, further sprayings could be restricted to the number necessary to keep damage to no more than one hole on average per wrapper leaf of the cabbage. This approach is reported to be an effective alternative to reliance on regular weekly or fortnightly sprays (Srinivasan 1984). The adoption of visual damage thresholds on wrapper leaves of cabbage also results in considerable reduction in the number of sprays (three to five) compared to the weekly spraying adopted currently by growers (Srinivasan 1984). Srinivasan further reports a definite possibility of eliminating pre-heading sprays, since the larval populations causing damage to either outer leaves, or to leaves about to cover the head, do not reduce marketable yield significantly.

Use of insecticides

Cabbage One of the early recommendations for DBM control on cabbage involved application of malathion, carbophenothion, parathion or phosphamidon (Verma and Sandhu 1967, Abraham and Padmanabhan 1968). Gupta and Sharma (1971) obtained excellent control of this species with one application of endrin at 0.25 kg AI/ha followed by two sprays of dimethoate at 0.5 kg AI/ha. A spray schedule of one spray of endrin three weeks after planting followed by two applications of dimethoate at every three weeks has also been reported to be the most effective and economical control measure (Joshi and Sharma 1976). Sachan and Srivastava (1975) conducted several field experiments for the control of this pest and observed the best protection following fortnightly

Ecology and Management of D B M in India 69

sprays until harvest of either 0.03% endrin or 0.075% lindane or 0.20% carbaryl. Singh et al (1976) reported that application of quinalphos at the rate of 0.25 kg AI/ha resulted in 100% mortality of larvae within 48 h of spraying. Three spray applications of 0.06% phenthoate at fortnightly intervals beginning 20 days after transplanting was found to reduce the incidence of the pest (Gowda et al 1977). Rajamohan and Jayaraj (1978) reported that applications of fenthion, endosulfan, fenitrothion, dichlorvos, and carbaryl were effective for upto 10 days in reducing larval population and damage (Table 3). Ramasubbaiah and Lal (1978) found phosphamidon applied at 0.05% effectively con- trolled the DBM larvae on cabbage. In other studies the application of quinalphos, methamidophos, dioxathion or endosulfan at 0.5 kg AI/ha gave effective control of larvae (Krishnaiah and Jagan Mohan 1977). Excellent control of the larvae has also been reported using spray applications of the following insecticides: chlorpyriphos, dioxathion (0.5 kg AI/ha), monocrotophos (0.3 kg AI/ha), phosalone, phenthoate, and methomyl (0.5 kg AI/ha) (Krishnaiah et al 1978). Srinivasan and Krishnakumar (1982) have observed that permethrin or fenvalerate applied on early cabbage varieties at 75 g AI/ha 30 and 40 days after planting provided effective control. Carbofuran at 1.5 kg AI/ha is reported to protect the crop against DBM for up to 45 days after planting (Sarode and Kumar 1983). Shah et al (1984) recommend application of permethrin (0.2 kg AI/ha), or fenvalerate (0.1 kg AI/ha), sulprofos (1 .0 kg AI/ha) or prothiophos (0.75 kg AI/ha) for the control of this pest.

Table 3. Efficacy of different insecticides and Bacillus thuringiensis (Bt) on the control of DBM

Treatment Dosage /plant befor reduction % at D A T damage (%) No. larvae Larval population Leaf

at 10 DAT (kg treatment 1 2 10

Malathion Dichlorvos Phoxim Endosulfan Fenitrothion Fenthion Carbaryl BHC Carbaryl Bt

0.50 0.50 0.50 0.35 0.50 0.50 0.50 1.25 2.50 2.50

3.5 4.2 3.8 4.5 3.6 4.8 2.9 3.0 3.9 4.1

53 58 44 69 58 53 61 47 44 77

77 75 68 77 78 73 80 69 71 83

61 65 60 54 76 65 65 21 34 25

43cd 24ab 41 cd 22a 23ab 20a 30abc 46de 34bcd 36cd

Control 3.8 + + 55e ªSource: Rajamohan and Jayaraj 1978. in each vertical column followed by the same letter are not significantly different at 5 % level according to Duncan's Multiple Range Test. after treatment. d Population increased.

DAT: Days

Cauliflower Control of DBM on cauliflower has been achieved by sprays of 0.025% diazinon, 0.1% trichlorfon, 0.1 % mevinphos, 0.08% malathion or 0.2% carbaryl (Verma and Sandhu 1968). The authors also opined that application of either mevinphos or malathion was more suitable for control on cauliflower, especially at the time of curd formation, owing to the short residual toxicity of the compounds. Among 20 insecticides tested as direct sprays for the control of DBM, treatment with 0.025% diazinon, 0.15% chlorfenvinphos, 0.1% trichlorphan or 0.01 % mevinphons is reported as effective, resulting in 100% mortality of the larvae within 24 h (Verma et al 1973). Evaluation of insecticides on cauliflower grown as a seed crop has showed that sprays of phosalone at 0.05% or phenthoate at 0.05% are effective against DBM larvae (Regupathy and


Paranjothi 1980). Sprays of phosalone at 0.05% and 0.1% for the control of this pest on cauliflower have been reported to reach below tolerance limit of 2 ppm in 5.91 and 8.95 days, and the half life values to be 3.15 and 2.83 days, respectively (Murthy et al 1982). The effectiveness of synthetic pyrethroids viz cypermethrin at 60 and 80 g AI/ha, fenvalerate at 80 and 100 g AI/ha, permethrin at 125 g AI/ha and deltamethrin at 10 g AI/ha for the control of larvae was reported by Awate et al (1982) and Gandhale et al (1982).

Use of bacterial pathogens

The effectiveness of Bacillus thuringiensis Berliner (Thuricide) applied in the form of dust, wettable powder, or emulsion for the control of DBM under laboratory, field, and glasshouse conditions has been reported (Narayanan et al 1970). Varma and Gill (1977) tested the effectiveness of four commercial preparations of B. thuringiensis along with NPV specific to DBM under laboratory conditions. They found Thuricide HPSC and Dipel WP to be more promising at 1 and 1.5 g product/l of water than Bactospeine or Thuricide 90 TS. Rajamohan and Jayaraj (1978) reported the effectiveness of Biotrol for the control of larvae, with a persistence effect of about 10 days. Weekly sprays of Dipel (0.5 kg product/ha) were quite effective in controlling larvae on cabbage and the degree of efficacy was also comparable to that of fortnightly sprays of methamidophos and quinalphos (0.5 kg AI/ha) (Krishnaiah et al 1981).

Cultural Practices

Tomato, when intercropped with cabbage, has been reported to inhibit or reduce DBM egg-laying (Vostrikov 1915, Buranday and Raros 1973, Sivapragasam et al 1982). The reduction in oviposition and subsequent development of the pest was essentially due to emission of volatile compounds. Srinivasan (1984) conducted experiments involv- ing different combinations of cabbage-tomato intercropping at Bangalore. He reported that there was no reduction in the incidence of DBM larvae when different combinations of cabbage and tomato were planted at the same time (Table 4). According to his study, however, a planting pattern of one row of cabbage and one row of tomato (the cabbage planted 30 days later than the tomato), afforded greater reduction of DBM larvae on cabbage. The reduction in larval incidence was attributed to the release of volatile substances from the late crop growth stages of tomato which inhibited DBM oviposition.

Table 4. Influence of intercropping on the marketable yield of cabbage, in relation to infestation by DBMª

Cabbage yield

Crop combination

1 row C and 1 row T 2 rows C and 2 rows T 3 rows C and 2 rows T 4 rows C and 1 row T C alone

Mean

planting time Mean C and planted C planted 15 days C planted 30 days yield t/ha

together later than T later than T 0.578a 2.878a 5.333a 2.930a 0.611a 2.817a 4.300b 2.576a 0.583a 2.844a 4.322b 2.583a 0.604a 2.773a 1.519b 0.608a 0.650b 0.800c 0.596 2.392 3.187

ªSource: Srinivasan 1984. signifcantly different at 5 % level according to Duncan’s Multiple Range Test.

in each vertical column followed by the same letter are not C = cabbage, T = tomato.


The spreading foliage of full-grown tomato plants also hid the cabbage leaves from the female moths and thus reduced oviposition. Srinivasan further opined, however, that this reduction in larval incidence was not manifested in any significant increase in the marketable yield of cabbage compared to the yield recorded from sprayed plots.

Use of selective insecticides

Studies on the relative toxicity of certain conventional insecticides and synthetic pyrethroids has been made against the adults and cocoons of A . plutellae, an important parasitoid of DBM larvae. The results indicate that permethrin, fenvalerate, cypermethrin, deltamethrin, and phosalone are safer to adults and cocoons of A . plutellae. Quinalphos was found to be detrimental to both stages of this parasitoid. Dichlorvos, monocrotophos, and endosulfan were found to be highly toxic to adults but relatively safe to cocoons of A . plutellae (Mani and Krishnamoorthy 1984).

Insecticide resistance

In Punjab, Deshmukh and Saramma (1973) observed that populations of DBM collected from Jullundhar were less susceptible to parathion than those found in Ludhiana. Fairly high tolerance to parathion, fenitrothion, malathion, DDT and endrin was also reported from Punjab by Chawla and Kalra (1976).

I ntegra ted Pest M anagem en t Approaches

Based on exhaustive studies conducted on the population dynamics of DBM on cabbage, Jayarathnam (1977) recommends spraying the crop with an organophosphorus insecticide only when the economic threshold was reached. He also recommends sprinkl- ing a 5% jaggery solution in order to encourage the activity of predatory ants like Tapinoma melanocephalum, Pheidole sp and Camponotus sericeus. Further, the removal of old leaves of cabbage (where 60% of pupation occurrs) is also recommended as one of the cultural practices likely to reduce incidence of pest. Nagarkatti and Jayanth (1982) found parasitism by A . plutellae showed a clear density dependent relationship with the host during the rainy and winter seasons at Bangalore. Hence, they suggest spraying a suitable insecticide relatively safer to this parasitoid. Since the population of parasitoids is low during summer months, they suggest inundative release of A . plutellae to maintain the pest below economic injury level. These suggestions should be implemented only when cabbage/cauliflower is affected by DBM.

In recent years, increasing levels of infestation of the leafwebber, C. binotalis, has also occured on cabbage, along with that of DBM (Nagarkatti and Jayanth 1982, Srinivasan 1984). The late larval instars of C. binotalis prefer to feed on primordia and this usually resulted in either aborted heading or multiple heading (Srinivasan 1984). Recognizing a potential need for the development of a suitable management strategy effective against both these lepidopterans, Srinivasan (1984) suggested the monitoring of low damage thresholds on wrapper leaves of cabbage after giving a blanket spray to protect the primordia with phosalone at 0.07%. Phosalone is recommended in view of its effectiveness against both lepidopterans and its relative safety to important natural enemies of the pest complex on cabbage. The adoption of visual damage thresholds also results in considerable reduction in the number of spray applications of phosalone (Srinivasan 1984) (Figures 2 and 3). Superimposition of damage thresholds on the intercrop combination of one row of cabbage and one row of tomato (cabbage planted 30 days


later than tomato) is also advocated as an effective alternative approach to reducing the incidence of both pests and increasing cabbage yields significantly (Table 5 ) .

Table 5. Effect of visual damage threshold linked insecticide application on cabbage yield in cabbage-tomato intercropping

Marketable yield of cabbage (t/ha) No.of sprays

1 row cabbage (C) and 1 row tomato (T) 2 9.789a (C maintained with 0.5 hole in wrapper leaves) 1 row C and 1 row T (C sprayed at weekly intervals) 1 row C and 1 row T (C not sprayed till harvest) C alone maintained with 0.5 hole in wrapper leaves C alone sprayed at weekly intervals C alone not sprayed till harvest

9

4 9

9.900a 6.285b

10.054a 10.317a

ªSource: Srinivasan 1984. different at 5 % level according to Duncan's multiple range test. planted 30 days later than tomato (T)

b Means in vertical column followed by the same letter are not significantly In all treatments, cabbage (C) was

60 mean holes in wrapper leaves (- Weekly sprays

0.1 2 .0 0

0.3 - F o r t n i g h t l y spray

0.2

0.1

1.0 in wrapper leaves

2.0 mean holes in wrapper leaves

0 10 20 50 60

.5 mean holes in wrapper leaves (-

4 mean holes in leaves about t o c o v e r ( - ) 8 mean holes in leaves about to

3.0

Days after planting

10.0 mean holes in outer leaves (- 20.0 mean holes in outer leaves (---

1.0

0.4

0. I

Figure 2. Population of DBM larvae on cabbage at different days after planting in the rainy season 1982. Arrows indicate insecticide application. (Srinivasan 1984)

0. I

0 0.2

0. I

0 0.3

0.2

0.1

0.5

0.3

0.2

0. I

0


Weekly sprays

Fortnightly sprays

0.5 mean hole in wrapper leaves

1.0 mean hole in wrapper leaves

2.0 mean holes in wrapper leaves

20 40 50 60 70

4 holes in leaves about to cover(- 10 holes in outer leaves (---)

0.6

0.4 0.3

0.2

0.1

-

I

4

2.0

I

0.

20 30 40 50 60 70 Days after planting

Figure 3. Population of DBM larvae on cabbage at different days after planting in the winter season 1982. Arrows indicate insecticide application. (Srinivasan 1984)

Literature Cited

Abraham, E. V. and M. D. Padmanabhan. 1968. Bionomics and control of diamondback moth, Plutella xylostella Curtis, Indian J . Agric. Sci. 38:513-519.

Atwal, A. S. 1955. Influence of temperature, photoperiod and food on the speed of development, longevity, fecundity and other qualities of diamondback moth, Plutella maculipennis Curtis (Lepidoptera: Tineidae). Aust. J. Zool. 3: 185-221.

Awate, B. G., D. N. Gandhale, A. S. Patil, and L. M. Naik. 1982. Control of diamondback moth, Plutella xylostella L. with synthetic pyrethroids. Pestology 6: 11-12.

Buranday, R. P. and R. S. Raros. 1973. Effects of cabbage-tomato intercropping on the incidence and oviposition of the diamondback moth, Plutella xylostella (L). Philipp. Entomol. 2:369-374.

Chacko, M. J. 1968. Macromalon sp. a parasite of Plutella maculipennis Curt. in Assam (India). Tech. Bull. Commonw. Inst. Biol. Control 19:97-102.


Chand, P. and R. Choudhary. 1977. Patterns of insect plant relationships determining susceptibility of food plants in the diamondback moth, Plutella xylostella (L) Curtis. Mysore. J . Agric. Sci. 11:547-549.

Chawla, R. P. and R. L. Kalra. 1976. Studies on insecticide resistance in Plutella xylostella Linn. Indian J. Plant Prot. 6:170-180.

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Bioecology and management of diamondback moth in India

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