mosquito behavior and vector control

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Annu. Rev. Entomol. 2005. 50:53–70 doi: 10.1146/annurev.ento.50.071803.130439 Copyright c 2005 by Annual Reviews. All rights reserved First published online as a Review in Advance on July 13, 2004 MOSQUITO BEHAVIOR AND VECTOR CONTROL Helen Pates and Christopher Curtis London School of Hygiene & Tropical Medicine, London WC1E 7HT, United Kingdom; email: [email protected]; [email protected] Key Words endophily, biting time, oviposition site choice, mosquito dispersal, competitive mating, monogamy Abstract Effective indoor residual spraying against malaria vectors depends on whether mosquitoes rest indoors (i.e., endophilic behavior). This varies among species and is affected by insecticidal irritancy. Exophilic behavior has evolved in certain popu- lations exposed to prolonged spraying programs. Optimum effectiveness of insecticide- treated nets presumably depends on vectors biting at hours when most people are in bed. Time of biting varies among different malaria vector species, but so far there is inconclusive evidence for these evolving so as to avoid bednets. Use of an untreated net diverts extra biting to someone in the same room who is without a net. Understand- ing choice of oviposition sites and dispersal behavior is important for the design of successful larval control programs including those using predatory mosquito larvae. Prospects for genetic control by sterile males or genes rendering mosquitoes harmless to humans will depend on competitive mating behavior. These methods are hampered by the immigration of monogamous, already-mated females. RESTING BEHAVIOR INRELATION TO HOUSE SPRAYING The spraying of the walls and ceilings of houses with residual insecticides such as DDT reduces the survival prospects of indoor resting Anopheles mosquitoes sufficiently to greatly reduce the chance of malaria transmission (47); this was the key method by which malaria was eradicated in the temperate zones and in reducing malaria incidence in India from 75 million cases per year in the 1930s to 110,000 per year in the 1960s (99.8% reduction). There are now serious problems of physiological resistance to DDT in some Indian vector species (79). In addi- tion, behavioral resistance in vectors in some countries has arisen in response to prolonged spraying programs. This can have an impact on a control effort and may result from an immediate response to the irritant insecticides (DDT or pyrethroids), or it may be a genetic trait evolved under selection from the presence of insecti- cides in houses. Insecticide irritancy can be demonstrated by a strong stimulation to take off and fly, a high proportion of mosquitoes exiting from a treated house, or both. 0066-4170/05/0107-0053$14.00 53 Annu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.org by INFLIBNET Master on 04/18/09. For personal use only.

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27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCE10.1146/annurev.ento.50.071803.130439Annu. Rev. Entomol. 2005. 50:5370doi: 10.1146/annurev.ento.50.071803.130439Copyright c 2005 by Annual Reviews. All rights reservedFirst published online as a Review in Advance on July 13, 2004MOSQUITO BEHAVIOR AND VECTOR CONTROLHelen Pates and Christopher CurtisLondon School of Hygiene & Tropical Medicine, London WC1E 7HT,United Kingdom; email: [email protected]; [email protected] Words endophily, biting time, oviposition site choice, mosquito dispersal,competitive mating, monogamyAbstract Effective indoor residual spraying against malaria vectors depends onwhether mosquitoes rest indoors (i.e., endophilic behavior). This varies among speciesand is affected by insecticidal irritancy. Exophilic behavior has evolved in certain popu-lations exposed to prolonged spraying programs. Optimumeffectiveness of insecticide-treated nets presumably depends on vectors biting at hours when most people are inbed. Time of biting varies among different malaria vector species, but so far there isinconclusive evidence for these evolving so as to avoid bednets. Use of an untreatednet diverts extra biting to someone in the same room who is without a net. Understand-ing choice of oviposition sites and dispersal behavior is important for the design ofsuccessful larval control programs including those using predatory mosquito larvae.Prospects for genetic control by sterile males or genes rendering mosquitoes harmlessto humans will depend on competitive mating behavior. These methods are hamperedby the immigration of monogamous, already-mated females.RESTING BEHAVIOR IN RELATIONTO HOUSE SPRAYINGThe spraying of the walls and ceilings of houses with residual insecticides suchas DDT reduces the survival prospects of indoor resting Anopheles mosquitoessufcientlytogreatlyreducethechanceofmalariatransmission(47);thiswasthe key method by which malaria was eradicated in the temperate zones and inreducing malaria incidence in India from 75 million cases per year in the 1930s to110,000 per year in the 1960s (99.8% reduction). There are now serious problemsof physiological resistance to DDT in some Indian vector species (79). In addi-tion, behavioral resistance in vectors in some countries has arisen in response toprolonged spraying programs. This can have an impact on a control effort and mayresult froman immediate response to the irritant insecticides (DDTor pyrethroids),or it may be a genetic trait evolved under selection from the presence of insecti-cides in houses. Insecticide irritancy can be demonstrated by a strong stimulationto take off and y, a high proportion of mosquitoes exiting from a treated house,or both.0066-4170/05/0107-0053$14.00 53Annu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCE54 PATES

CURTISThe irritating effect of DDTwas demonstrated in verandah trap huts (82), wheremosquitoes inside sprayed huts were irritated and exited huts sooner than thosein unsprayed huts. This bite and run behavior has been shown in populations ofAnopheles gambiae sensu stricto in the Tanga region of Tanzania (31), where highproportions leaving the sprayed house were fully engorged and displayed a highight activity. Similarly, a 94% exit rate of An. gambiae and An. funestus frompyrethroid-treated huts was observed in Burkina Faso (23). A change in the placeof egress for A. gambiae s.s. mosquitoes, from the windows to the eaves, has alsobeen recorded in huts sprayed with tetramethrin (81).In Tanzania, Mnzava et al. (55) found that a higher number of fed AnophelesarabiensiswereexitingDDT-sprayedhousesthanlambda-cyhalothrin-sprayedhouses, fromwhichmost exitingmosquitoeswereunfed. Thisdifferencewasconsidered to be partly due to the excitorepellent properties of DDT, although hostavailability also inuenced the response of An. arabiensis to the two chemicals. Inthe DDT-sprayed areas, most cows were kept indoors, and mosquitoes thereforehad to go inside to take a blood meal and were then driven out by the effects of theDDT. Fewer cows were kept indoors in the lambda-cyhalothrin-treated area, andthis insecticide had a higher impact on malaria transmission than did DDT becauseit acted rapidly by either deterring mosquitoes from feeding or killing them.Irritancy may not always be counterproductive. DDT was reintroduced in the1980s in India, where Anopheles culicifacies is DDT resistant. Some reduction inmalaria transmission was achieved because the irritant effect of DDT lasts muchlonger than the toxic effect (92). A comparison of DDT and bendiocarb in Mex-ico found that both insecticides had a similar impact on the incidence of malaria(45), but the mode of action of the two insecticides on the local vector, Anophelespseudopunctipennis, was different (DDT is a much more irritant insecticide thanbendiocarb; 26). DDT caused a decrease in the indoor resting densities and a ten-dency to avoid biting humans (46), whereas bendiocarb resulted in high mortalitybut no signicant reduction in the number of indoor biting mosquitoes.Naturally Endophilic Anopheles SpeciesThe term endophily refers to the preference of a female mosquito to rest indoorsduringtheperiodbetweentheendoffeedingandtheonset ofthesearchforan oviposition site. Residual house spraying is likely to be effective only if themosquito species concerned is endophilic or at least partially endophilic, becausethe mosquito needs to rest on the insecticide-treated walls for a sufcient time ifit is to pick up a lethal dose. Naturally endophilic species include An. gambiaes.s. and An. funestus in Africa, An. culicifacies in India, and An. minimus in EastandSoutheastAsia.DDThouse-sprayingprogramsinthe1940sand1950sinVenezuela and Guyana (32) were successful in the coastal areas because housesprovided the only safe resting place for Anopheles darlingi mosquitoes. However,eradication was impossible in forested areas because of the existence of wildpopulations outside human settlements. In Suriname and Colombia, An. darlingiAnnu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCEMOSQUITO BEHAVIOR AND CONTROL 55appearstohavedevelopedashorterindoorrestingperiodowingtoinsecticidepressure (76).In Greece in the 1950s, DDT spraying programs led to exophilic behavior in theoriginally endophilic local vector, Anopheles sacharovi. It was considered that thesurvival of this species was due to a high level of irritability and physiological resis-tance (24). However, it is also possible that An. sacharovi became more zoophilicduring the spraying campaign (4). Similarly, malaria transmission by Anophelessundaicus in southern Java was not controlled by DDT house spraying, becauseof increased exophily (84). A decrease in the number of An. sundaicus resting onsprayed walls at night was observed, yet large numbers were still recovered fromhuman bait.In India, malaria control is based on indoor spraying of insecticides. A majorresurgenceofmalariaoccurredaftertheslackeningoftheeradicationprograminthe1970s(2)andincreasedproblemsofphysiologicalresistance(79). Thiswas exacerbated by the development of irrigation schemes and the movement ofsusceptible human populations into risk areas as well as the existence of outdoorresting populations of the major malaria vector, An. culicifacies. DDT spraying inKarnataka state began in 1945, and in one district in the 1970s, Anopheles uviatilis(naturally endophilic) was found resting largely outdoors and only entering housesto take blood. Similarly, in the state of Tamil Nadu, outdoor resting populationsof An. culicifacies with DDT resistance were found. Malathion spraying in 1978replacedDDTspraying, whichsuccessfullyreducedtheindoorbitingdensity.However, owing to the high gametocyte load in the community and the presenceof outdoor transmission, a low-grade transmission in the area was maintained.In Hainan Island, China, residual house spraying, launched in 1959, eliminatedthe main malaria vector, An. minimus, but recent malaria outbreaks have incrim-inated this vector again. Entomological surveys have shown a complete changeinthebehaviorofAn.minimus,whichisnowexophagic(i.e.,itentershumandwellings to take its blood meal) exophilic and has an equal preference for hu-mans and cattle (41a).Endophagic-Exophilic Anopheles SpeciesControl ofexophilicvectorsbyresidual housesprayingisusuallyineffective.However, if the vector species is endophagic, then there is still a good chance thathouse spraying will be at least partially effective if a suitable chemical is used,such as fenitrothion, which has a fumigant effect.Important successes have been achieved by using impregnated bednets againstanotherendophagicbutexophilicvector,Anophelesdirus,inHainanProvince,China, where the malaria incidence was high despite DDT residual spraying untilthe introduction of deltamethrin-treated bednets (17).Predominantly endophilic mosquito populations may include varieties that ex-hibit exophilic tendencies. This tendency may be selected for by the use of in-secticides or other human interventions such as deforestation; it was consideredAnnu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCE56 PATES

CURTISthe reason for the failure of a World Health Organization (WHO) house sprayingcontrol program in the district of Garki, Nigeria, to interrupt malaria transmissionashadbeenthedeclaredaimoftheproject(56). Itwasestimatedthatbeforespraying began in Garki, only about half the blood meals were followed by indoorresting (57). Populations composed of some consistently endophilic individualsand other consistently exophilic ones apparently led to nonuniformexposure of themosquito population to the insecticide; the exposed fraction of the population maybe so much affected that it nearly disappears. However, the unexposed fractionof the population persisted to ensure that sufcient transmission continued, eventhough major reductions in malaria mortality were noted.Culex and Aedes MosquitoesResidual house spraying is now rarely used as a control method against Culex orAedes mosquitoes. This is partly because many vector species have outdoor restinghabitsorrest indoorsonunsprayedobjectssuchasclothesorcurtains. Culexmosquitoes exhibit an innate tolerance to residual insecticide deposits, possiblyowing to the pulvilli beneath Culex tarsi (6).MOSQUITO BEHAVIOR IN RELATION TOINSECTICIDE-TREATED NETSInsecticide-treated bednets or curtains have a remarkable impact on the incidenceof malaria in several Asian countries and on African child mortality (41, 63). In1910 Ross (75) had recommended bednets as a protection against malaria becauseof the late-night biting tendency of most anophelines. For most efcient anthro-pophilic vector species suchas An. gambiae (35), An. funestus (35), andAn. nili (35)(Figure 1a) in Africa; An. dirus (74) and An. minimus (38) (Figure 1b) in South-east Asia; and An. anthropophagus (69; Xu Bozhao, unpublished data) in ChinaFigure 1 Percentage of the nights biting by the anopheline vector species in variousparts of the world that occurred starting at the times indicated on the x axis. Data basedon human landing catches outside houses except in the case of An. anthropophagus,in which the catches were inside, andAn.albimanus, in which indoor and outdoorcatches are compared. (a) Africa (Bobo-Dioulasso, Burkina Faso) (35). (b) SoutheastAsia [An. dirus in Thailand (74); An. minimus in Assam, India (38)]. (c) China [dataon An. anthropophagus from Anhui, Hubei, Zeijiang, Guizhou, and Yunnan Provinces(69) and on An. sinensis from Hubei and Hunan Provinces (Xu Bozhao, unpublisheddata)]. (d) Indian subcontinent (An. culicifacies species A and An. stephensi in Punjab,Pakistan; cold months: NovemberMarch; hot months: AprilOctober) (66). (e) SouthAmerica [An. darlingi in southern Brazil (29) and Suriname (36); An. nuneztovari inVenezuela (77)]. ( f ) Central America (An.albimanus: indoor and outdoor biting inGuatemala, Honduras, Nicaragua, Costa Rica, and Panama) (60).Annu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCEMOSQUITO BEHAVIOR AND CONTROL 57Annu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCE58 PATES

CURTISFigure 1 (Continued)Annu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCEMOSQUITO BEHAVIOR AND CONTROL 59(Figure1c), thebitingrhythmandthetimeswhenmostpeoplegotobedandget up (assumed to be 2200 and 0500 h in rural areas) should ensure that morethan 75% of anopheline bites would be prevented by mosquito-proof bednets. Thesame applies to An. culicifacies (66) in Pakistan in hot weather, but in cold weatheralmost all biting is completed before 2000 h, presumably before low temperaturesinactivate the mosquitoes (Figure 1d). In South America (Figure 1e) more than75% of the biting of Anopheles nuneztovari (77) is between 2200 and 0500 h, butAn. darlingi populations have different biting rhythms in different areas (29, 36).In Suriname the rhythm is similar to that of An. nuneztovari, but in southern Brazilmuch of the biting occurs before 2200 h and after 0500 h.In Central America, much of the biting by An. albimanus occurs outdoors andbefore 2200 h (60) (Figure 1f ). There is a strong tendency for older, parous An.albimanus (which are the only ones that can carry infective sporozoites) to biteearlier than the rest of the population (60). The mean parity rate was 49% before2200 h, 30% from then until 0500 h, and 17% thereafter. The early high parityrate would further reduce the protection from malaria transmitted by this speciesthatonewouldexpecttobeachievablewithbednets. Surprisingly, however, aconsiderableeffect ofnetsonmalariatransmittedbyAn. albimanushasbeenreported (71).Tendenciesforsignicantlyhigherparityorsporozoiteratesamongearlierbiters have been recorded in several studies on An. gambiae and Anopheles farauti(see tabulation in Reference 53). The proportion of the nights sporozoite positivebites by An. gambiae s.s. and An. funestus occurring between 2200 and 0500 hwas about 88% (53).It has been feared that the effectiveness of nets may be reduced if the bitingrhythm changes in a community where net use is widespread (40). Charlwood &Graves (12) found a marked shift toward earlier biting by An. farauti when netswere introduced in Papua NewGuinea. They attributed this not to a genetic changein the population but to the fact that mosquitoes returning to a netted village fromegg laying during the night would have difculty in obtaining a blood meal beforedawn. Thus many would remain hungry during the day and would attempt to nda meal as soon as dusk fell.For An. gambiae s.l. two studies comparing treated and untreated villages havereported little or no difference in biting rhythm (49, 64), but two other studies (54,58) reported a marked shift in biting time in those houses.The above-mentioned studies were carried out soon after net introduction, whenselection for genetic changes in behavior could hardly be expected. However, bitingtimes of An. funestus have recently been recorded (59), nearly three years afterintroductionoftreatednetsintoavillage,whichmightbeexpectedtobelongenough for genetic changes to occur. The same percentage of the nights bitingoccurred between 2300 and 0500 h in this village and in a village without nets.Furthermore, studies conducted six years after net introduction (5) showed that themean biting time remained unchanged but that there were indications of a widerrange of biting times after dusk and before dawn.Annu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCE60 PATES

CURTISIn comparison with untreated nets, pyrethroid-treated nets are much more ef-fective in reducing malaria incidence (38, 41, 52) presumably because of one ora combination of the following effects of pyrethroids on mosquitoes. (a) Contactwith the nets may drive mosquitoes away before they have had a chance to pen-etrate the nets and bite (43), thus enhancing the physical protection provided bythe net. This effect is due to the excito-repellency and rapid knockdown effect ofpyrethroids. Such diversion away from treated nets may lead to more blood feedstaken from nonhuman hosts (12) from which the Plasmodium species that infecthumans could not be acquired. However, highly anthropophilic species refuse to bediverted fromhumans, and the human blood index remains high even when almosteveryone in a village is using a treated net (49). (b) Mosquitoes attracted to the odorof sleeping humans may be killed in sufcient numbers so that widespread use ofnets in a community leads to a decline in vector population density and survival,which results in few mosquitoes surviving long enough for malarial sporozoites tomature inside them. In village-scale studies in which almost everyone was providedwith a treated net, major reductions in vectorial capacity of the village mosquitopopulationshavebeenobservedinTanzania(18, 4952), BurkinaFaso(10),D.R. Congo (39), Guinea Bissau (37), and Assam, India (38). However, in SierraLeone the results were equivocal (48), and in The Gambia (42, 65) and Thailand(83) such effects have not been found. The explanation of the latter results may bethat the mosquito populations of treated and untreated control villages shared thesame breeding places, thus leading to continual mixing of the populations so thatthe effects of mass mosquito killing may be obscured in the trial results (65).A study in Tanzania in which one person in a room was provided with a treatednet showed that this markedly reduced the amount of biting by An. arabiensis (amember of the An. gambiae complex) on another person in the same room withouta net, compared with when neither had nets (43). This is presumably because manymosquitoes, which would have attacked the unprotected person in the absence ofnets, rested on the treated net long enough to be killed or repelled from the hut.However, when a person with an untreated net sleeps in the same hut as someonewithoutanet, morebitingisdivertedtothelatterpersonthanwouldoccurifneither person had a net (43). There are indications (C.A. Maxwell, unpublisheddata)thatcurrenteffortsinnortheastTanzaniatoincreasenetusagebysocialmarketing are leading to a situation in which a considerable proportion of adultsbuy nets for their own use, but seldom buy nets for their children and few of thenets are treated with insecticide. Nets used in this way are expected to lead to anincrease in the malaria risk for vulnerable children. This contrasts with programsof organized free provision that can ensure that all age groups are provided witheffective insecticidal nets (19).BEHAVIOR IN RELATION TO LARVAL CONTROLIdentication of breeding sites is necessary for control measures such as sourcereduction, commonly used for Aedes aegypti control. Knowledge of ovipositionbehavior can help identify breeding sites and monitor populations. When usingAnnu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCEMOSQUITO BEHAVIOR AND CONTROL 61chemicals for control of immatures, choosing the correct larvicide and larvicideformulation is critical. For example, oviposition traps containing a high concen-tration of emulsiable chlorpyrifos were repellent to ovipositing Aedes triseriatus(3). Because granular formulations of chlorpyrifos and temephos are not repellent,it may be that the additives and/or solvents in the emulsiable concentrate wererepellent, rather than the insecticidally active ingredient. Ovitraps can help mon-itor oviposition activity (68) and are also useful for collecting samples of adultsfor the detection of arboviruses (13).Choice of Oviposition SitesThe distribution of larvae is generally determined by the oviposition site selectedby the female. For example, mosquitoes may selectively avoid oviposition in watercontaining notonectids, sh, and tadpoles (72). Arelease-and-recapture study withAe. aegypti in Puerto Rico (25) showed signicantly higher rates of recapture inhouses where suitable breeding containers had been added than in houses wherecontainers had been removed. This is taken as indirect evidence that dispersal ofAe. aegypti is driven by the search for oviposition sites. This has important impli-cations because vector control efforts with this species center on source reduction,i.e., removal or destruction of breeding sites. Increased adult dispersal caused byfemales searching for a suitable breeding site may increase the spread of virusessuch as dengue (67).An. dirus, themainmalariavectorinpartsofSoutheast Asia, isgenerallyexophilic and lives in forests, where it feeds on primates. Movement of people intoforested areas creates ideal transmission conditions because they provide a readyfoodsupplyandcreate manyof the small, stagnant transitorypools usedas breedingsites by this mosquito (73). It is extremely difcult to nd and destroy all thesebreeding sites. In Bangladesh, larvae appear to exhibit a particular behavior (73)to aid survival under harsh conditions. Immatures appeared to be adapted to andpossibly dependent on small temporary pools. Females were observed depositingeggs at the water line, where they embryonate and can remain viable for up totwoweeks. Heavyrainresultsinasynchronoushatchthat leadstocompletedevelopment in 56 days and hence waves of biting females. During dry periods,larvae were observed leaving a draining pool before it became completely dry andcrawlingasfaras53cm,sometimessuccessfullyndinganotherpool.Larvaewerealsorecoveredalivefromdrainedpools,upto94hafterbeingstranded.Many of the metazoan cohabitants that would have preyed on them or competedwith them for food were eliminated in the same pool as it dried up. Fourth instarswere also observed cannibalizing the rst or second instars of the same species.Larvivorous Fish and ArthropodsMuch effort has been devoted to optimizing biological control by metazoan preda-tors such as sh, Toxorhynchites, and Mesocyclops. However, larvivorous marshsh are often ineffective in controlling synchronous mosquito broods during peri-ods of heavy rainfall or tidal intrusion because of the immediate hatching of largeAnnu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCE62 PATES

CURTISnumbers of mosquito eggs, the dilution of predatory sh densities due to increasedwater levels, and a delayed increase in sh numbers (9). Ae. taeniorhynchus nor-mally oviposits on exposed salt marsh and mangrove soil and has been observedavoiding ovipositing near water with a high sh concentration (72). It is possiblethat in such areas prolonged wet weather can result in smaller mosquito popula-tions, because there is a decrease in the number of sites free of sh when the watertable rises (9).Toxorhynchites brevipalpis is a tree-hole-breeding mosquito widely distributedin tropical Africa (89) that feeds on both surface prey (small animals sharing thehabitat or other animals on the water surface or trapped in the air-water interface)and subsurface prey (mosquito larvae and other small animals) (44). On detectionof surface prey, T. brevipalpis assesses both the angle and the distance to its preyand uses this information to optimize the approach path (44). The effectiveness ofthis predatory behavior seems dependent on temperature, because in the laboratoryit has been found that one T. brevipalpis destroys an average of 154 Ae. aegyptilarvae whenrearedat 26Candupto359larvae at 32C(9). Toxorhynchites spp. ex-hibit killing behavior both in the eld and in the laboratory (86). This behavior ischaracterized by the killing but not consumption of prey larvae and conspecics.Oneproposedexplanationofthisbehavioristhevulnerablepupahypothesis,whereby larvae are protecting their own interests before pupation by slaughteringas many of their competitors as possible, because the onset of killing begins whenthe larva reaches a critical weight in the fourth instar, which also permits pupation(14). Killing of prey larvae also deprives earlier instars of food, slowing develop-ment and increasing the chance of cannibalism (14). Toxorhynchites spp. appearto have a level of efcacy similar to that obtained with larvivorous sh and theywould probably be good biological control agents in thick rain forests or perido-mestic habitats (89). Studies on the oviposition behavior of T. rutilus rutilus inLouisiana, United States, indicated that this species has little value as a biocontrolagent of Ae. aegypti and Culex quinquefasciatus in the urban environment becausethe primary larval habitat of the latter two species is articial containers, whereasT. rutilus rutilus preferentially breeds in tree-holes (27). However, a 45%reductionin Ae. aegypti densities in New Orleans, Louisiana, was achieved with weekly re-leasesofToxorhynchitesambionensis(Doleschall)(28). Thedegreeofcontrolachieved did not increase by increasing the number of T. ambionensis adults re-leased each week and little movement of T. ambionensis between each study sitewas observed. The results from this study indicate that use of T. ambionensis asa biocontrol agent against container-breeding mosquitoes in urban situations maybe feasible.GENETIC CONTROLThe term genetic control covers all methods by which a mechanism for pest orvector control is introduced into a wild population through mating. These include(a)thesterileinsectreleasemethodorsterileinsecttechnique(SIT),inwhichAnnu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCEMOSQUITO BEHAVIOR AND CONTROL 63males are sterilized by irradiation or other means and released to mate with wildfemales, causing them to lay sterile eggs; and (b) introduction of genetic factorsinto wild populations that render pests harmless to humans.Sterile Insect TechniqueMuch research was carried out about 30 years ago, especially in India and El Sal-vador, on the application of SIT to mosquitoes, but this research virtually stoppedin the mid-1970s, not because the method was a technical failure, but because ofpolitical problems in India (91) and the intensifying civil wars in Central America.There is now a revival of interest, especially in the use of transgenesis to improvesex separation so that only nonbiting males are released and to ensure that theirfemale progeny die without the need for radiation or chemosterilization (1, 87).Three issues of mosquito behavior are especially relevant to SIT: (a) matingcompetitiveness of articially reared, sterilized males; (b) dispersal/migration; and(c) female monogamy/polygamy.MATINGCOMPETITIVENESS Doubts about whether sterilization or articial rear-ingmightleadtobehavioralabnormalitiesnotdetectableincagesledtoeldtests in which uorescently marked males were released and the population wasthensampledtoascertainthesterile:fertilemaleratioforcomparisonwiththesterile:fertile mating ratio, as shown by the fertility of the eggs laid by capturedfemales. To ensure that the females tested were not immigrants but had mated inthe presence of the sterile males, virgin females of wild origin were released intothearea,giventimetomate,andthenasmanyaspossiblewerecollectedandallowed to oviposit. This procedure was used with (a) chemosterilized Anophe-les quadrimaculatus (22), (b) chemosterilized An. albimanus carrying a geneticsex separating system (21), (c) chemosterilized or cytoplasmically incompatibleCx. quinquefasciatus (33), and (d) chemosterilized or chromosomally translocatedand sex ratiodistorting Ae. aegypti (34, 78). All showed moderately good matingcompetitiveness.Thus,adequatelylargereleaseswellmixedwithisolatedwildpopulations might have been expected to yield high levels of egg sterility. How-ever, in practice they frequently did not do so. This has been attributed to an inuxof already-mated females from outside the sterile-male release area.The rst cage tests of the tness of transgenic Anopheles and Aedes yielded poorresults (11, 36a) possibly because of inbreeding depression. Whether transgenicmosquitoes with adequate competitiveness can be selected is now a key researchquestion.DISPERSAL/MIGRATION Dispersal abilityisamajorconcernfortheSIT(a)toensure that sterile males are released near enough to all emerging wild femalesso that they have a fair chance of mating with them; and (b) to assess whetherthere are appreciable numbers of immigrant females that have already had fertilematings and will lay fertile eggs and nullify the effect of the sterile releases.Annu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCE64 PATES

CURTISAe. aegypti was considered a poorly dispersing species and sterile males wouldneed to be released at intervals of about 50 m along urban streets to nd all thelocal females (70, 80). However, more recent studies with rubidiumlabeling foundlabeled eggs from the same group of released females scattered over more than an800-m radius (67). With Cx. quinquefasciatus a 3-km-wide barrier zone aroundreleasevillageswasexpectedtobeadequatetoisolatethem, butuorescentlymarked sterile males were frequently found 7 km from their release point and eggrafts continued to be laid throughout the barrier zone, within which great effortshadbeenmadeusinglarvicidestoeliminateallemergenceofadults(93). ForAn. albimanus, release of competitive sterile males intoa 20km2area protectedbyabarrier zone in which breeding was prevented by methoprene treatment of potentialbreeding sites had a major suppressing effect on the population compared with theupward seasonal trend seen in an untreated area. However, even though the barrierwas 4 kmwide, it seemed insufcient to ensure isolation (21). Thus, there seems tobe a tendency to consider immigration negligible until the indigenous populationis eliminated by sterile releases, after which immigrants make their presence felt.Clarication of the true proportion of immigrants in a population is important notonly for the SIT, but also for assessing whether local efforts at larval control withinsecticides or environmental management could have a worthwhile impact on theadult vector population or whether they are likely to be swamped by immigration.FEMALEMONOGAMY/POLYGAMY Most laymenandsomescientistsbelievethatsuccessful application of SIT is limited to species in which the females are monog-amous. This belief is based on an incorrect assumption that radiation or chemicalsterilization involves elimination of sperm so that a female mated to a sterile and afertile male would be fully fertile. However, dominant lethal mutations in Dipteradonotinactivatespermbutkillafterzygoteformation,sothatsomeeggsofamultiply-mated female are sterilized (90). Thus, female polygamy is no barrier tothe successful application of SIT. On the contrary, it would be a great advantagebecauseafterarrivalinthereleasearea,immigrantinseminatedfemaleswouldbe willing to accept sterilizing matings. However, unfortunately, for mosquitoesmonogamy is the rule.In Ae. aegypti, monogamy appears to result from the action of a peptide, giventhe name matrone (15, 30), that is carried in the seminal uid produced in the maleaccessory glands and inhibits the reception of sperm from second and subsequentmatings. However, Klowden (39a) has recently shown that in An. gambiae andAn. albimanus, in contrast to Ae. aegypti, implantation of male accessory glandsinto females did not prevent them from receiving sperm when they were mated.Bryan (7, 8) studied the effects of mating females of the An. gambiae complex tosterile aspermic hybrids that are produced by laboratory crosses between differentmembers of the complex. The females that had been mated to aspermic hybridswere subsequently mated to fertile males, and these females were tested for abilityto lay fertile eggs. When the hybrid males used in these experiments had An. melasas their female parent, these hybrids could inhibit their mates from being fertilizedAnnu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.27 Oct 2004 14:10 AR AR234-EN50-03.tex AR234-EN50-03.sgm LaTeX2e(2002/01/18) P1: GCEMOSQUITO BEHAVIOR AND CONTROL 65in their subsequent matings. However, when the hybrid males had An. melas astheir male parent, the hybrids failed to inhibit fertilization in the subsequent mating.Bryan (8) explained these contrasting results with the different hybrids as being dueto the underdeveloped male accessory glands observed in the latter type of hybridbut not the former, and she assumed that the latter type could not produce matronebut the former type could do so. However, in view of the above-mentioned recentevidence for the apparent irrelevance of male accessory glands (39a) to monogamyin Anopheles, the interpretation of the data of Bryan (7, 8) needs to be reconsidered,especially if hybrids in the An. gambiae complex are ever to be tried again as ameans of genetic control (23a).Introduction of Genetic Factors into Wild PopulationsIt is the strong tendency toward monogamy of mosquitoes that renders local ef-forts at genetic control futile, unless one can either (a) guarantee isolation of thepopulation, as may be the case with urban populations that are surrounded by ruralpopulations of a different species; (b) afford a huge rolling program of release,as with the screwworm program, so that immigrant females mostly receive sterilematings before they can reach the area in which the eradication effort is currently inprogress; or (c) replace SIT with the use of insects genetically engineered to carrya genetic driving system tightly linked to a gene that renders the insect harmlessto humans (16). The twin aims of the latter concept are that the desirable gene willbe driven to spread from a modest initial seeding and that the driving action willcounteract the effect of immigration. Among the challenges facing such a schemearebehavioralbarrierstofreecross-matingintheeld,suchasthosebetweenthe Mopti, Savannah, Bamako, and other chromosomally recognizable forms ofAn. gambiae s.s. in West Africa (88). Clearly, one would have to ensure that thereleased mosquitoes belong to the same formas the target population. Further con-siderations of behavioral-ecological issues surrounding this method are discussedin a recent book (85).The genetics of effective driving factors and genes for physiological nonsuscep-tibilitytomalaria, or other pathogens, are beyondthe scope of this review. It must berecognized that such genes would place strong selection on the pathogen to evolveevasionmechanisms.Thisproblemcouldbeavoidedbyusingageneticfactorthat renders a mosquito harmless by making it willing to bite only nonhuman ani-mals (i.e., zoophily). Marked differences in the degree of zoophily/anthropophilyexist between An. gambiae and An. quadriannulatus (61, 62), which can be cross-mated in the laboratory with fertile female progeny, so that crossing genes causingzoophily into the genetic background of An. gambiae may be possible.ACKNOWLEDGMENTSWe are grateful to colleagues who provided us with unpublished or inaccessibleinformation. Present address for Dr. Helen Pates is Ubwari Research Centre ofthe Tanzanian National Institute for Medical Research, Box 81, Muheza, Tanga,Tanzania.Annu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. 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WHO Chron. 30:1313992. World Health Organisation. 1986. Resis-tance of vectors, and reservoirs of diseaseto pesticides. World Health Organ. Tech.Rep. Ser. 73793. YasunoM, MacdonaldWW, CurtisCF,Grover KK, Rajagopalan PK, et al. 1978.Acontrol experiment with chemoster-ilisedmaleCulexpipiens fatigans inavillage near Delhi surrounded by abreeding-freezone. Jpn. J. Sanit. Zool.29:32543Annu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.P1: JRXOctober 28, 2004 21:8 Annual Reviews AR234-FMAnnual Review of EntomologyVolume 50, 2005CONTENTSBIOLOGY AND MANAGEMENT OF INSECT PESTS IN NORTH AMERICANINTENSIVELY MANAGED HARDWOOD FOREST SYSTEMS,David R. Coyle, T. Evan Nebeker, Elwood R. Hart,and William J. Mattson 1THE EVOLUTION OF COTTON PEST MANAGEMENT PRACTICES INCHINA, K.M. Wu and Y.Y. Guo 31MOSQUITO BEHAVIOR AND VECTOR CONTROL, Helen Patesand Christopher Curtis 53THE GENETICS AND GENOMICS OF THE SILKWORM, BOMBYX MORI,Marian R. Goldsmith, Toru Shimada, and Hiroaki Abe 71TSETSE GENETICS: CONTRIBUTIONS TO BIOLOGY, SYSTEMATICS, ANDCONTROL OF TSETSE FLIES, R.H. Gooding and E.S. Krafsur 101MECHANISMS OF HOPPERBURN: AN OVERVIEW OF INSECT TAXONOMY,BEHAVIOR, AND PHYSIOLOGY, Elaine A. Backus, Miguel S. Serrano,and Christopher M. Ranger 125FECAL RESIDUES OF VETERINARY PARASITICIDES: NONTARGETEFFECTS IN THE PASTURE ENVIRONMENT, Kevin D. Floate,Keith G. Wardhaugh, Alistair B.A. Boxall, and Thomas N. Sherratt 153THE MEVALONATE PATHWAY AND THE SYNTHESIS OF JUVENILEHORMONE IN INSECTS, Xavier Bell es, David Martn,and Maria-Dolors Piulachs 181FOLSOMIA CANDIDA (COLLEMBOLA): A STANDARD SOILARTHROPOD, Michelle T. Fountain and Steve P. Hopkin 201CHEMICAL ECOLOGY OF LOCUSTS AND RELATED ACRIDIDS,Ahmed Hassanali, Peter G.N. Njagi, and Magzoub Omer Bashir 223THYSANOPTERA: DIVERSITY AND INTERACTIONS, Laurence A. Mound 247EFFECTS OF PLANTS GENETICALLY MODIFIED FOR INSECTRESISTANCE ON NONTARGET ORGANISMS, Maureen OCallaghan,Travis R. Glare, Elisabeth P.J. Burgess, and Louise A. Malone 271viiAnnu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.P1: JRXOctober 28, 2004 21:8 Annual Reviews AR234-FMviii CONTENTSINVASIVE PHYTOPHAGOUS PESTS ARISING THROUGH A RECENTTROPICAL EVOLUTIONARY RADIATION: THE BACTROCERA DORSALISCOMPLEX OF FRUIT FLIES, Anthony R. Clarke, Karen F. Armstrong,Amy E. Carmichael, John R. Milne, S. Raghu, George K. Roderick,and David K. Yeates 293PHEROMONE-MEDIATED AGGREGATION IN NONSOCIAL ARTHROPODS:AN EVOLUTIONARY ECOLOGICAL PERSPECTIVE, Bregje Wertheim,Erik-Jan A. van Baalen, Marcel Dicke, and Louise E.M. Vet 321EGG DUMPING IN INSECTS, Douglas W. Tallamy 347ECOLOGICAL, BEHAVIORAL, AND BIOCHEMICAL ASPECTS OF INSECTHYDROCARBONS, Ralph W. Howard and Gary J. Blomquist 371THE EVOLUTION OF MALE TRAITS IN SOCIAL INSECTS,Jacobus J. Boomsma, Boris Baer, and J urgen Heinze 395EVOLUTIONARY AND MECHANISTIC THEORIES OF AGING,Kimberly A. Hughes and Rose M. Reynolds 421TYRAMINE AND OCTOPAMINE: RULING BEHAVIOR AND METABOLISM,Thomas Roeder 447ECOLOGY OF INTERACTIONS BETWEEN WEEDS AND ARTHROPODS,Robert F. Norris and Marcos Kogan 479NATURAL HISTORY OF PLAGUE: PERSPECTIVES FROM MORE THAN ACENTURY OF RESEARCH, Kenneth L. Gage and Michael Y. Kosoy 505EVOLUTIONARY ECOLOGY OF INSECT IMMUNE DEFENSES,Paul Schmid-Hempel 529SYSTEMATICS, EVOLUTION, AND BIOLOGY OF SCELIONID ANDPLATYGASTRID WASPS, A.D. Austin, N.F. Johnson, and M. Dowton 553INDEXESSubject Index 583Cumulative Index of Contributing Authors, Volumes 4150 611Cumulative Index of Chapter Titles, Volumes 4150 616ERRATAAn online log of corrections to Annual Review of Entomologychapters may be found at http://ento.annualreviews.org/errata.shtmlAnnu. Rev. Entomol. 2005.50:53-70. Downloaded from arjournals.annualreviews.orgby INFLIBNET Master on 04/18/09. For personal use only.