Journal of the American Mosquito Control Association, 18(2):97-99, 2OO2Copyright @ 2002 by the American Mosquito Control Association, Inc.

LANDING SITES ON THE HUMAN BODY PREFERRED BYAEDES ALBOPICTUS

YOSHIKAZU SHIRAI,I HISASHI FUNADA,I KIYOSHI KAMIMURA,I TAISUKE SEKI, A.NOMASAAKI MOROHASHI]

ABSTRACT, The landing sites on the human body preferred by Aedes albopictus were examined. Five male

volunteers wearing only shorts stood in a mosqu:ito net enclosure containing 120 proboscis-amputated Ae, al'bopictus. In separate tests, 9 male volunteers and I female volunteer lay supine during the test. The number of

mosquitoes landing on each site of the volunteer's body was counted, and after completion of the test, his or

her body temperature was recorded. When the subject was upright, the Ianding site most preferred by mosquitoes

was the foot. When volunteers were supine, the foot also was tbe most preferred landing site, but the proportion

of mosquitoes landing on the foot in this position in comparison with other sites was lower than when thevolunteer was in the upright position. The 2nd most preferred landing site was the hand, lbllowed by the face.No correlation was found between preferred landing sites and body temperature. Factors other than temperature(e.g., human emanation) may influence mosquito behavior and landing site.

KEY WORDS Preferred landing site, foot, hand, body temperature, Aedes albopictus

INTRODUCTION

Studies have reported the landing sites on thehuman body preferred by Culex quinquefosciatusSay (Self et al. 1969), Anopheles albimanus Wied(Knols et al. 1994), Anopheles atroparvus YanThiel, and Anopheles gambiae Giles (De Jong andKnols 1996). When subjects were sitting or supine,Cx. quinquefascicttus preferred the lower leg,whereas Anopheles spp. preferred upper sites ofthebody. In Japan, Aedes albopictus Skuse is the mostcommon mosquito. In this study, we examined thecorrelation between landing sites on the humanbody that were used by Ae. albopictus and bodytemperature at those sites. We also examined land-ing sites on volunteers in both upright and supinepositions.

MATERIALS AND METHODS

Mosquitoes: We used colonized Ae. albopictus,originally collected in Ogaki in Gifu Prefecture, Ja-pan. We perfbrmed tests with 20- to 30-day-old un-fed female mosquitoes, because previous testsshowed that mosquitoes of this age were more avidfeeders than were younger females.

Volunteers: Five healthy male volunteers, 19-30years of age, were used in the upright position test.Nine male volunteers (including the 5 males usedin the upright test), 19-30 years of age, and I fe-male volunteer,2T years of age, were used in thesupine position test. The tests were conducted dur-ing evening hours, and all volunteers had not

I Department of Biodefence Medicine, Faculty of Med-icine, Toyama Medical and Pharmaceutical University,2630 Sugitani, Toyama 93O-O194, Japan.

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

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

bathed and had engaged in I h of light exercise.During the test, male volunteers wore only shorts.The female volunteer wore a sleeveless shirt andculottes.

Landing test: We adapted a mosquito net (150X 100 X l8O cm) as a test cage and introduced 120female mosquitoes into it during the evening. Theproboscises of the mosquitoes were amputated be-fore placing them into the net (Shirai et al. 2000)because mosquito bites might cause serious itching,skin damage, or hypersensitivity. Amputated mos-quitoes approach humans and attempt to bite sim-ilarly to nonamputated mosquitoes. The followingevening, volunteers entered the net after completingtheir exercises, and remained still while either up-right or supine. A scorer outside the chambercounted the number of mosquitoes landing on eachsite of volunteer's skin or clothes every 2 min for11 min (Fig. 1). For each position, we scored thepercent landing as the percentage of the number ofmosquito landings on each site compared with thetotal number of landings.

Skin temperature: After the landing tests, ther-mograms of volunteers in the upright position wererecorded by a thermotracer (6T67, Nippondenki-sanei Co., Ltd., Tokyo, Japan). Furthermore, theskin temperature at each site of the body was mea-sured by a radiant thermometer (IT-340S, HoribaCo. Ltd., Kyoto, Japan). Experiments were ana-lyzed and evaluated statistically with the Bonfer-roni-Dunn test and Pearson's correlation coefficientof StatView (1998).

RESULTS

Preferred landing sites on subjects in theupright position

When in the upright position, the foot was thelanding site most preferred by Ae. albopictus.'Ilteaverage number of mosquito landings on the dorsalsurface of the foot was 45.6 + 8.1. which was sis-

97

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and high, according to biting preference. They re-ported that An. atroparvzs preferentially bites re-gions of high skin temperature, but that An. gam-biae tends to bite regions of low temperature. Wefound no correlation between skin temperature ofbody sites and landing rates. The reason Ae. albop-ictus landed mostly on the foot may be that feetemanated characteristic odors, as discussed by DeJong and Knols (1996). In this study, the numberof landings on the foot when in the upright positionwas greater than when in the supine position. Thismay indicate that Ae. albopictus ordinarily rests ata relatively low position in relation to the groundand often seeks biting sites initially at lower posi-tions, and then flies upward to bite only if neces-sary. Nonetheless, the foot was preferred in the su-pine position as well, and this suggests that themain factor is not the position, but attractive sub-

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Fig- 3. Mean t SE number of landings on each siteof supine volunteers by Aedes albopictus (10 replicates).Different letters show signitricant differences (P < 0.0001)by the Bonferroni-Dunn test.

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skin temperature (C)

Fig. 4. Percent landing on each site of upright vol-unteers by Aedes albopictus and skin temperature mea-sured by a radiant thermometer and supported by a ther-motracer.

stances. Many people report that their feet are oftenbitten by mosquitoes, but one must consider thatthe feet and legs are frequently exposed during hotweather. Although the forearms and hands are alsoexposed in the summer, they are usually in motionmore than the feet and legs, thus discouraging mos-quito biting. Even when the subject is still and notrepelling mosquitoes (as in this study), Ae. albop-icras prefers the foot, then the leg, the hand, andthe face.

ACKNOWLEDGMENTS

We thank several students of Toyama Medicaland Pharmaceutical University for their help in ourexperiments. We also thank Ines Tomoco Matsusefor reviewing the manuscript.

REFERENCES CITED

De Jong R, Knols BGJ. 1996. Selection biting sites bymosquitoes. ln: Olfaction in mosquito-host interactionsWiley, United Kingdom: Ciba Foundation. p 89-108.

Dekker I Takken W' Knols BGJ, Bouman E, De Laak S,De Bever A, Huisman PWT 1998. Selection of bitingsites on a human host by Anopheles gambiae s.s., An.arabiensis and An. quadriannulatus. Entomol Exp Appl87:295-3U).

Knols BGJ, Takken W, De Jong R. 1994. Influence ofhuman breath on selection of biting sites by Anophelesalbimanus. J Am Mosq Control Assoc lO:423-426.

Self LS, Abdulcader MHM, Tun MM. 1969. Preferred bit-ing sites of Culex pipiens fatigans on adult Burmesemales. Bull WHO 4O:324-327.

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

StatView. 1998. StatView user's rtanual Carv. NC: SASInstitute,

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