Journal of the American Mosquito Control Associntion, 18(2):91-96,2O02Copyright @ 2W2 by the American Mosquito Control Association, Inc.

ALCOHOL INGESTION STIMULATES MOSQUITO ATTRACTION

YOSHIKAZU SHIRAI.' TAKAO TSUDA,' SHINYA KITAGAWA,' KEN NAITOH,3 TAISUKE SEKI,4KIYOSHI KAMIMURAI eNN MASAAKI MOROHASHI5

ABSTRACT. Mosquito bites should be avoided because of the risk of contracting parasitic and viral diseases

such as malaria, dengue fevet, and several encephalitides. Although humans have been said to suffer more

mosquito bites after ingesting liquor, little is known about whether that is true. Thirteen volunteers (12 men

from 20 to 58 years old and a 24-year-old woman) were chosen as test hosts and a 3O-year-old man was

established as a control. We measured ethanol content in sweat, sweat production, and skin temperature before

and after ingestion of 350 ml of beer (ethanol concentration 5.5Vo) by volunteers and compared them with a

control subject. Our study demonstrated that percent mosquito landing on volunteers significantly increased after

beer ingestion compared with before ingestion, showing clearly that drinking alcohol stimulates mosquito at-

traction. However, ethanol content in sweat and skin temperature did not show any correlation between alcohol

ingestion and mosquito landings. This study shows that persons drinking alcohol should be careful about their

increased risk to mosquito bites and therefore exposure to mosquito-borne diseases.

KEY WORDS Ethanol ingestion, mosquito attraction, landing, sweat, Aedes albopictus

INTRODUCTION

The reason why people attract more mosquitoesafter ingestion of alcohol has been reported to per-haps be because the body produces more carbondioxide, more sweat, raises its temperature, or acombination of these (Yasutomi 1995). Carbon di-oxide has been shown to be a mosquito attractant(Brown et al. 1951) and heat is also an importantfactor in attracting mosquitoes (Smart and Brown1956, Eiras and Jepson 1994). Several studies alsohave reported increased mosquito attraction tosweat (Maibach et al. 1966, Khan et al. 1969, Healyand Copland 2000). Some researchers assume thathumans slowed by drinking alcohol are more easilybitten by mosquitoes. But in fact, the reason whyhumans attract mosquitoes after drinking alcoholhas not been studied and still remains unresolved.On the other hand, sweat contains ethanol after al-cohol ingestion and a good correlation exists be-tween ethanol concentration in sweat and that inblood (Kamei et al. 1998). However, a relationshipbetween ethanol in sweat and mosquito attractionhas not yet been fully studied. This purpose of thisstudy is to solve the question of whether mosquitoattraction to people after drinking alcohol is relatedto ethanol in sweat and skin temperature.

' Department of Biodefence Medicine, Faculty of Med-icine, Toyama Medical and Pharmaceutical University,2630 Sugitani, Toyama 930-0194, Japan.

2 Department of Applied Chemistry, Nagoya Institute ofTechnology, Gokiso, Showa, Nagoya 466-8555, Japan.

3 Department of Environmental Technology, Postgrad-uate School of Engineering, Nagoya Institute of Technol-ogy, Gokiso, Showa, Nagoya 466-8555, Japan.

a Seki Dermatological Clinic, 7331 Kurehamachi, To-yama 930-0138, Japan.

5 Department of Dermatology, Faculty of Medicine, To-yama Medical and Pharmaceutical University, 2630 Sug-itani, Toyama 930-0194, Japan.

MATERIALS AND METHODS

Mosquitoes and landing test: We used 4 coloniesof Aedes albopictus Skuse, maintained in our lab-oratory at24 + l"C,6O-7OVo relative humidity, anda 14:10 h light:dark photoperiod. Collection sitesof the 4 colonies were Ogaki in Gifu Prefecture,Ako in Hyogo Prefecture, Tsurumi Ryokuchi in

Osaka Prefecture and Ishigaki in Okinawa Prefec-ture, Japan. Mosquitoes used in the studies were 2-6 generations and 20- to 30-d-old unfed older fe-males, because we had found that older female Ae.albopictus had higher biting rates than did 3- to 5-d-old mosquitoes. An aquarium (600 X 295 x 360mm; NS-6M, NISSO Corporation, Tokyo, Japan)was used as a test chamber and proboscis-amputat-ed mosquitoes were used for the tests (Shirai et al.2000). Thirty-five proboscis-amputated mosquitoesand a plastic cup containin! a 3Vo sugar solutionwere introduced into the chamber. The left forearmsof 1 subject and a control were simultaneously in-serted through the sleeve into the test chamber withthe back of the hand facing up, while keeping asmall space between the palm and the bottom sur-face of the test chamber (Fig. 1).

The determination of sweat and skin tempera-ture: Skin temperatures of hands and forearms ofhuman subjects were measured at 6 points with aradiant thermometer (IT-340S, Horiba Co. Ltd.,Kyoto, Japan) before and after each attraction test.The probe of the apparatus for measuring continu-ous sweating rate (model Kenz-Perspiro 201, Su-zuken, Nagoya, Japan) was attached to each thumbof both subjects throughout the tests. The sweatproduction was electrically recorded every 0.1 secwith a personal computer (Fig. l).

The apparatus for the determination of ethanolconcentration in sweat: The apparatus for measur-ing ethanol concentration in sweat consisted of 4parts. A sampling probe was attached to the skinsurface (made by modifying the probe used in model

JuNs 2002 Moseuno ArrnacrroN BY ALCoHoL INGEsrloN

Table l. Mean (tSE) difference of skin temperature and sweating rate before and after ethanol ingestion in groups

A and R. Diff'erence in percent landing in group A is 31.7 + 4.'7, and that of group R is -28.5 = 5.0.

Group A,atuacting (n - 25)

Group R,repel l ing (n: 14) Pl

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Difference in skin temperature (oC)

Difference in sweating rate(mg/cm'�lmin)

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NS'

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' By Mann-Whitney U-test.'� NS, not significant.

the volunteers each ingested 350 ml of beer (etha-nol concentration 5.57o) during the next l-12 min.The control subject did not drink any liquor afterthe preingestion test. The postingestion attractiontest also was performed 3 times for l0 min eachwith a 3-min interval. The percent mosquitoes land-ing on each volunteer's forearm was calculated by100 X (number of landings on a volunteer)/(thesum of numbers of landings on the volunteer and acontrol). Both percent landings were analyzed sta-tistically by a Student's /-test. We measured skintemperature, sweat on forearms, and ethanol con-tent in sweat with an apparatus for determinationof ethanol concentration (Kamei et al. 1998). Eachof the 13 volunteers was tested 3 times in 1 seriesof tests. Thus, 39 (13 x 3) tests were conducted.The tests were separated into 2 groups to observethe attraction (group A) and the repellency (groupR) of mosquitoes after ethanol ingestion by the sub-jects. Statistical analysis on groups A and R wasdone by a Mann-Whitney U-test.

Comparison between tolerant and nontolerantsubjects: On a questionnaire given to the volun-teers, 5 men answered that they did not drink orcould drink only a small amount of liquor (the non-tolerant [NT] group), whereas 7 men and 1 womananswered that they could drink normal or largeamounts (the tolerant [T] group). Group T (n : 8x 3) and group NT (n : 5 X 3) were statisticallyanalyzed by a Mann-Whitney U-test.

RESULTS

Mosquito landing

Mosquitoes preferred landing on forearms afterethanol ingestion by the subject. The percent ofmosquitoes landing on a volunteer's forearm in-creased significantly after ethanol ingestion (P <

0.0001, paired r-test; Fig. 3) and showed that hu-man forearms attract more mosquitoes after etha-nol ingestion by the subject. Twenty-five of the 39tests showed an increased number of landings afterethanol ingestion by the subject and the other 14tests showed a decreased number of mosquitolandings.

Influence of skin temperaturet sweatproduction, and ethanol content in sweat

The skin temperature of volunteers rose in groupA and declined in group R, and no significant dif-ference was found. The sweating rate also was notsignificantly different between the 2 groups, and thesweating rate decreased after ethanol ingestion inboth groups, but in group A it decreased less thanin group R (Table l). After ethanol ingestion, theethanol content and the percent of ethanol increasedand reached a maximum at 23-33 min, and thendecreased (Fig. 4). No significant difference wasobserved between groups A and R for ethanol con-tent per 30 sec, the percent of ethanol in sweat, and

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Fig. 5. Mean (+SE) cumulative sweat production before (A) and

the cumulative sweat production before and afterethanol ingestion in any of those measurements(Figs. 4 and 5). In group A, the mean continuoussweat production for 10 min increased after ethanolingestion (Fig. 6,4), but sweat production decreased

in group R (Fig. 6B). The cumulative sweat pro-duction during each test for volunteers and controlwas calculated every l0 min. The cumulative sweatproduction slightly decreased even after ethanol in-gestion and was significantly lower than the con-

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(attractant); (B) group R (repellent). In (A), the sweating rate before and after ingestion is almost the same, but duringthe last half, the sweating rate after ethanol ingestion was slightly higher than before ingestion. In (B), the sweatingrate after ethanol ingestion was less than before ingestion.

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Fig.7. Change of cumulative sweat production of volunteers (n : 13) and control at 6 times before and after

ethanol ingestion. Results are reported as means + SE. During the lst l0 min, the cumulative sweat production between

volunteers and control was not significant, but thereafter, significant differences were found. *, P < 0.05; **, P <

0.01; xxx, P < 0.001 by Student's /-test. After ethanol ingestion, the cumulative sweat production of volunteers

gradually decreased compared to the constant level of the control.

trol, except for the 10 min interval during the firstattraction test (Fig. 7).

Comparison between tolerant andnontolerant subjects

After ethanol ingestion, group T attracted moremosquitoes than did group Nl but the difference wasnot statistically significant. The average skin temper-ature of group T rose after ingestion but that ofgroupNT declined slightly, but again the difference was notsignificant. No difference was found in the sweatingrate (Table 2). Group T showed a slightly higher eth-anol content and percent of ethanol than did groupNT at 23-33 min and at36-46 min, but the differencewas not statistically significant (Fig. 8).

DISCUSSION

Our study clearly demonstrated that ingestingethanol results in attraction of more mosquitoes. Li-quor ingestion has been reported to possibly resultin the attraction of mosquitoes because of increasedlevels of carbon dioxide exhaled and during still-ness, for example (Yasutomi 1995). In our study,exhaled carbon dioxide and that release due to themovement of forearms were excluded from consid-

eration because of the technique used. However,carbon dioxide escaping from forearm skin wouldbe a possible consideration. After ethanol ingestion,exhaled carbon dioxide increases with time (Men-delson 1968), and the body temperature falls slight-ly (Graham and Dalton 1980, Graham 1981, Fel-lows et al. 1984). After ethanol ingestion, skintemperatures on the arm have been reported to in-crease in a room atZloC but to decrease in a roomat -23"C (Livingstone et al. 1980). The body tem-peratures of rats that received injections of ethanolalso decreased (Stewart et al. 1992). Concerningthe change in sweat after ethanol ingestion, alco-holics without neurologic deficits showed moresweat responses on the palms and soles than didnonhabitual drinkers (Chida et al. 1998). In ourstudy, the skin temperature increased in subjectsthat attracted mosquitoes and decreased in subjectsthat repelled mosquitoes. No significant differencewas found between the 2 groups, but skin temper-ature might have some influence on mosquito land-ing. Because the skin temperature of alcohol-tol-erant subjects also increased, whereas that ofalcohol nontolerant subjects decreased, tolerance toalcohol might correlate with mosquito atffaction. Inthis study, we demonstrated that sweat glands se-creted ethanol after ingestion, as has been previ-

Table 2. Mean (+SE) difference in percent landing, skin temperature, and sweating rate in groups T and NT.

Group Nlnontolerant( n : 1 5 ) P '

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ously reported (Kamei et al. 1998). However, verysmall amounts of ethanol might not be a major fac-tor in attracting mosquitoes after ingestion. Ethanolin sweat increased trom 23 to 33 min after ethanolingestion and then decreased (Fig. a), but mosquirolandings were not influenced by this change. Sweathas been reported to attract mosquitoes (Maibachet al. 1966, Khan et al. 1969), and human sweatand 2-oxopentanoic acid have been reported to elic-it mosquito landings (Healy and Copland 2000).However, other studies have shown that sweat isnot universally attractive (Howlett 1910, Rudolfs1922), but is attractive only at low vapor concen-trations and is significantly repellent at high con-centrations (Brown et al. 1951, Skinner et al. 1965).

In conclusion, our research indicated that hu-mans attract more mosquitoes after ingesting etha-nol. We can conclude that sweat production or skintemperature after ethanol ingestion does not attractmosquitoes but the attraction rather might be dueto the presence of unknown chemical substances onthe skin after ethanol ineestion.

ACKNOWLEDGMENTS

We thank Hisashi Funada for valuable sugges-tions. We also thank Masao Kawai and several stu-dents of the Nagoya Institute of Technology, andthe staff of Suzuken Co., Ltd., fbr their help in ourexperiments. We also thank Ines Tomoco Matsusefor reviewing the manuscript.

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Chida K, Takasu ! Kawamura H. 1998. Changes in sym-pathetic and parasympathetic function in alcoholic neu-ropathy. Jpn J Alcohol Drug Depend 33:44-55.

Eiras AE, Jepson PC. 1994. Responses of f'emale Aedzsaegypti (Diptera: Culicidae) to host odours and convec-tion currents using an olfactometer bioassay. Bull En-tomol Res 84:.2O7-211.

Fef lows IW. Macdonald IA. Bennett T. '1984. The influence

B 0.0r

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of environmental temperature upon the thermoregulatoryresponses to ethanol in man. Clin Sci 66:733--739.

Graham TE. 1981. Thermal and glycemic responses duringmild exercise in *5 to -15oC environments followrngalcohof ingestion. Avint Space Environ Med 52:517-522.

Graham T, Dalton J. 1980. Effect of alcohol on man'sresponse to mild physical activity in a cold environ-ment. Aviat Space Environ Med 5l:793-796.

Healy TP, Copland MJW. 2000. Human sweat and 2-ox-opentanoic acid elicit a landing response from Anoph-eles gambiae. Med Vet Entomol 14:195-2OQ.

Howlett FM. 1910. The influence of temperature upon thebiting of mosquitoes. Parasitolo gy 3:41 9 -484.

Kamei T, Tsuda I Mibu Y Kitagawa S, Wada H, NaitohK, Nakashima K. 1998. Novel instrumentation for de-termination of ethanol concentrations in human perspi-ration by gas chromatography and a good interrelation-ship between ethanol concentrations in sweat andblood. Anal Chim Acta 365:259-266.

Khan AA, Maibach Hl, Strauss WG, Fisher JL. 1969. In-creased atffactiveness of man to mosquitoes with in-duced eccrine sweating. Nature 223:859-860.

Livingstone SD, Kuehn LA, Limmer RE, Weatherson B.1980. The effect of alcohol on body heat loss. AviafSpace Environ Med 57:961-964.

Maibach HI, Khan AA, Strauss WG, Pearson TR. 1966.Attraction of anhidrotic subjects to mosquitoes. Arc&Detmatol 94:215-217.

Mendelson JH. 1968. Ethanol-l-Cra metabolism in alco-holics and nonalcoholics. Scie nce 1 59 :3 19 -32O.

Rudolfs W. 1922. Chemotropism of mosquitoes. Bull N JAgric Erp Sra 367:5-23.

Shirai Y Kamimura K, Seki T, Morohashi M. 2000. Pro-boscis amputation facilitates the study of mosquito(Diptera: Culicidae) attractants, repellents and hostpreference. J Med Entomol 37:637-639.

Skinner WA, Tong H, Pearson T, Strauss W, Maibach H.1965. Human sweat components at t ract ive to mosqui-toes. Nature 20'7 :66I-662.

Smart MR, Brown AWA. 1956. Studies on the responsesof the female Aedes mosquito. Part VII.-The effect ofskin temperature, hue and moisture on the attractivenessof the human hand. Bull Entomol Res 47:89-lOl.

Stewart RB, Kurtz DL, Zweifei M, Li T-K, Froehlich JC.1992. Differences in the hypotherrnic response to eth-anol in rats selectively bred for oral ethanol preferenceand nonpref'erence. Psychopharmacology lQ6:169-17 4.

Yasutomi K. 1995. Mosquitoes that know blood groups ofhuman. In: Strange insects are amaTing lasecrs Tokyo,Japan: Koudansya. p 175.

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Fig. 8. Ethanol content per 30 sec (A) and percent ethanol in sweat (B) in groups T and NT.