Jounulr or run ArrannrcANMoseurro CoNrnol Assocrluot Vol. 7,No. 4

POTENTIAL FOR DENGUE IN : ECOLOGYWITH PARTICULAR REFERENCETO AEDES AEGYPTI

A. KEMP AND P. G. JUPP

NationaLInstitute for Virology,Department of Virolngy, (Jniuersityof the Witwatersrand,Priuate Bag X4, Sandringham,2 1 3 1, South Africa

ABSTRACT. Observationson prevalence,geographical distribution, utilization of artificial larval h-abitatsand anthropophilism were made on diurnil mosquitoesat seleci,edlocalities along the "o".t oi Natal and iniand in the Transvaal to identify potential vectors of dengue in South dfrica. iarvai collections made in artificial containers on the ground, the exposureof bariboo pots as ovitraps in trees and collection of mosquitoesbiting man showedthe following speciesas the most likely candidatesfor vectors: Aeles aegypti, Ae. d.em,e.illoni,Ae. simpsoni, Ae. sirelitziae, Ae. furcifer, Ae. cordellieri and, Eretmapoditesquinqtrcuittatus. The bamboo pols showed that Ae. aegypti' and AL. simpsoii;;t" ]t; most widespreadspecies, gc-cur{ng^9t,11 of 1} localities. Aedesaegypi"was the most prevalent species with meanpot index of 60.3 + 9.8% (SE) and abundanceindex ofb.a3 + 0.1b (SE). A"d"t aegypiiiu" frequently present as Iarvae in artificial containers at indices of Ll-83% (mean 56.8 + 5.6%,""S'E)and was the.most anthropophilicspecies with averagebiting rates of 10-29 per man-hour at ? iocaiities. Although.Ae..aegyptiwasabundant in the potsit Ndumu (northern Naial) and at Skukuza(eastern Transvaal), the local pop.ulationswere poorly_anthropophiiic at these localities. At some localities, populations of Ae. demeilloni,Ae. sirnpsoni aid, Ae. strefitziaehad averagebiting rates of s.+-g.e per mqn-!ou.r.Aedes.furcifer was collectedfor the first time at Durban, extendi"ngits dlstribution southward to latitude 29'53'S.

INTRODUCTION might begin.Furthermore, Ndumu (Natal) and the Magaliesberg and Mica (Transvaal) were Investigations of denguevectors in countries chosenprimarily for investigationsof non-an- outside South Africa have onlv incriminated thropophilic populations of Ae. aegyprtl,while aedinemosquitoes, mostly of the subgenus Ste- Tzaneen(northern Transvaal)was selectedfor gomyia. The rural endemic vector in Asia is its anthropophilic population; these Ae. aegypti Aedes(Stg.) albopirtus(Skuse), while the urban collectionswere relevant to the taxonomic studv vectorin Asia,West Africa and tropical America (Juppet al., in ms.).Observations were made on is Ae. (Sfg.\ aegypti (Linn.) (Gu6ler 1988).In prevalence, geographical distribution, utiliza- West Africa, other Stegomyla speciesapparently tion of artificial containers as larval habitats play the role of enzooticsylvan vector, together and diurnal biting activity on bait to with 2 speciesof the subgenusDiceromyia, i.e., determine to what extent different speciespos- Ae. (Edwards) furcifer and Ae. taylori Edvratds sessedecological attributes which (Cordellier made them et al. 1983,Roche et al. 1988).,Aedes likely denguevectors. aegypti is widespread in the tropical and sub- tropical areasin eastern South Africa (Muspratt 1956),while Ae.furcifer is limited to the tropical MATERIALS AND METIIODS areas of northern Natal and the northeastern Ouitrapsin trees:Bamboo pots simulating tree Transvaal(Jupp 1980). holes were exposed as ovitraps to collect tree Our Arbovirus Unit is engagedin a project hole breeding mosquitoes.Eggs, Iarvae and pu- designedto investigate tree hole and container pae were obtained from the various localities breedingAedes principally species, membersof mappedin Fig. 1 by exposingbamboo pots for the subgenera Stegomyi.a and Diceromyia, in extended periods ranging from 38 to 1bB days eastern South Africa. The objective is to assess betweenNovember 7, 1989,and May 17, 1990. these mosquitoesas potential vectors of dengue Eggswere also obtained by exposingblack plas- viruses which could participate in epidemic tic bottles of water containing woodenpaddles transmission should denguebe reintroducedinto for oviposition (Jupp and Mclntosh 1gg0) on a the country. The project has several aspects farm in the Magaliesberg mountains and at which have alreadybeen defined in a publication Mica. The ovitraps were suspendedin shady on the taxonomic status of Ae. aegypti popula- trees at heights ranging from 1 to 4 m above tions (Jupp et al., in ms.). This study is con- groundlevel. At the end ofthe exposureperiod, cerned with the ecologl of potential vectors. ovitraps were returned to the laboratory where Collectinglocalities were chosen along the Natal the eggswere hatchedby flooding with tap water coast and at Skukuza in the eastern Transvaal and adults reared out. The bamboo pot index as representingpoints where a dengueoutbreak for each speciesis defined as the percentageof Dncnrusen1991 Dnncun VEcroR EcoLocY 575 pots found to contain that species.The abun- rnyia) cordellierl Huang in the Ae. furcifer grottp danceindex is the number of mosquitoesat each (Huang 1986a). locality divided by the product of the number of pots and number of daysthey wereexposed. RESULTS Artificial containers: Mosquito larvae were sampled from water-retaining artificial con- Ouitrapsin trees:The results ofthe survey for tainers in motor car scrap yards, municipal rub- tree hole breeding mosquitoesby meansof bam- bish dumps and other peridomestic sites at var- boo pots are given in Table 1. Twenty-eight ious localities in Natal and in the Transvaal speciesin 3 generawere sampled at 8 Iocalities (Fig. 1) from November 5, 1988, to April 18, in Natal and 4 localities in the Transvaal (Fig. 1989.The following containershad culicinelar- 1). Toxorhynchitesbreuipalpus Theobald and Ae. vae and pupae: used tire casings (most com- aegypti utilized the pots most frequently at the monly), metal drums, floor pans and tire wells Natal localities (mean bamboo pot indices > in scrappedcars, paint cans,beverage cans and 50%).The most abundantspecies in Natal were' beveragecartons. Sampleswere taken from tires in order, Ae. dendrophilusEdwards, Ae. capensis containing water and leaf litter by dipping a Edwards and Ae. aegypti,while the most wide- ladle repeatedly into the water until at least 50 spread were, in order, ?r. breuipalptn and Ae. larvae and/or pupae had been obtained, or at simp soni(Theobald) followed by A e. aegypti,Ae. Ieast 3 times until it was evident that no culi- dendrophihts and,Ae.capensis. At the Transvaal cines were present. The other, more accessible localities Ae. aegypti had the highest pot index containerswere scrutinizedfor immature culi- and was the most abundant and widespread cines. Larvae were reared out in the Iaboratory species. and identified.Container indiceswere recorded Overall,Ae. aegypti andAe. sirnpsonioccurred as the percentageof containers found to contain at 11 of the 12 South African localities.Aedes Ae. aegypti. aegypti was found most often in the bamboo Human-baited collections:These collections pots(meanpot index:60.3 L9.8%, SE) and were carried out during the daytime becauseAe. was the most abundant species (mean abun. -r aegyptiand other speciesof Stegomyiaare diur- danceindex : 0.43 0.15,SE) except fot Ae. : + nal biters. Volunteers used test tubes to collect dendrophilus (mean abundanceindex 0-47 adult female mosquitoeswhich probed and en- 0.26). gorged on their bare legs and feet. The biting In the subgenus Diceromryia,Ae. cordellieri ratesthus obtained werebased on 2-5 volunteers occurredin bamboo pots at Ndumu in northern collectingin the open at suitablesites, usually Natal and, to a small extent, at Skukuza in the near artificial containers in the urban localities eastern Transvaal. Aedes furcifer utilized the and the bamboopot sites at Palm Beach, Ar- bamboo pots in Durban, Ndumu and Skukuza madale,Ndumu and Tzaneen.Collections were with pot indicesof 20,71 and47%, respectively. made over the months of January to April 1989' The abundancesofthe 2 specieswere low in all November 1989to February 1990and January cases. to February 1991,usually during 2 periods ofthe Artificial containers: Container indices were day, 0530-0930h and 1500-1900h. No collec- determined f.or Ae. aegypti (Table 2) because tions were undertaken during the crepuscular this was by far the most prevalent speciesoc- periods or at night. Collecting generallytook curring as Iarvae in artificial containers on the placeon dayswhen the prevailingclimatic con- groundand becauseof the known importanceof ditions were warm, humid, partly cloudy and the species as a vector of dengue and other calm; mosquitoes remained active during viruses outside South Africa. Nine of the 14 slightly windy conditions. Mosquitoeswere sep- localities where containers were sampled had aratedaccording to species,and biting rateswere containerindices greaterthan 50%, with the 3 calculated by combining data from several col- highestoccurring at Port Shepstone(83%), Em- lections per locality and dividing by the total pangeni(78%) and Dutban (76%).Other species number of man-hours invested (the collection quitefrequently encountered in thesecontainers effort). Observations were made on various as- werc Ae. simpsoni,Eretrnapodites quinque u itta- pectsof feedingbehavior. tus Theobald, Tx. breuipalpusand CuLexquin- Mosquito identification: The mosquito nomen- quefasciatusSay. The first 3 of these species clature followsthat of Knight and Stone (1977) were also found to be common in containers and Ward (1984)except where more recenttax- sampledin Eshowein Natal, althoughAe. ae- onomic revisions have occurred.These relate to gypti was uncommon when that locality was the transfer of certain Ae. (Aedimorphus)spe- sampledin November1988. cies into the subgenusAlbuginosus of Aedes(Re- Water-retaining plants: Larvae and pupae of inert 1986)and the descriptionof Ae. (Dicero- Ae. sirnpsoni and Ae. streLitziaeMuspratt were 576 JoURNALoF THEAMERTcAN Moseurro CoNrRor,AssocrenoN VoL. 7, No. 4

'lr r Bamboopols l O Artlllclalcontalners{- lO r Human-bltlng Je J C Bamboopots and human-blilng N

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TRANSVAAL

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M!gallsrberg- e Johannesburg

\..-^.-/^"r-. c ur"( i NATAL j Mlubatubaa Sl. Lucia Empangeni EshoweO Rlchards Bay

Slanger

\. ?j{:"'H#'Jn!ltii""

Fig' 1. South African localities where mosquitoeswere sampledin bamboopot ovitraps in trees, in artificial containers on the ground and by diurnal human baited collections.

collected from the leaf axils of Strelitzia nicolai orange t.l'ee,Strychnos madagascarienslsPoiret Regeland Koern (Strelitziaceae)at Palm Beach (Loganiaceae),at St. Lucia Estuary. and the immatures of Ae. demeillonlEdwards, Human-baited collections:Biting rates, as a Ae. simpsoni and Er. subsimplicipe.sEdwards measureof anthropophily, were significant for from Dracaenahookeriana Koch (Agavaceae)at Ae. aegyptiat 7 of the urban localities (10-29 Oslo Beach. Large stands of Strelitzia nicolai per man-hour:Table 2), althoughthe Johannes- and Dracaena hookerinna were also found in burg sample is probably not from a perennial undisturbed, indigenous, coastal forest on the population. Biting rates were generally low at farm, Armadale, about 14 km north of Port localities in Natal further north than Empan- Shepstone. Eretmapodites quinqueuittatus lar- geni, correlating with generally low abundances vae were collected from the dried, openedhusks (Table 1). Two adult collections at a Durban of the fruit of the black or spinelessmonkey site,spaced one month apart in early 1991,gave DrNcue Vecron Ecolocv 577

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Table 2. Aedes aegypti collections at various localities: artificial container indices for larvae and average biting rates in human-baited collections.

Larval collections Adult collections Biting rate No. containers Container (per man- Locality* examined index(%) Man-hours hour) Natal Port Edward 1n 47 OsloBeach 2.0 0 Palm Beach NF** 3r.2 tt.2 Port Shepstone 18 ; Park Rynie 54 4.0 18.0 Scottburgh 19 11 Durban 45 76 9.0 29.0 Sfanopr IJ 54 c.u t2.4 Empangeni 18 78 t< 18.0 Richards Bay 62 ta< 1.5 Mtubatuba 2I J.f 2.9 St. Lucia q 56 8.0 0.8 Mkuze 10 70 5.5 J.O Ndumu NF 5.0 0.2 Transuanl Johannesburg oo 45 2.0 13.0 Skukuza 70 1.8 0.5 Tzaneen I 1.0 10.0 * All Iocalities are urban except for Ndumu, which is rural; all sites in the urban localities are peridomestic exceptat Johannesburg,where it is domestic. +* NF : no artificial containersfound. biting ratesof 15 and 89 per man-hour,respec- andAe.strelitziae,whereas males of Ae. simpsoni tively. Both collectionshad taken place during and Er. quin4ueuittatus commonly occurred at the midday period, defined for our purposes as and restedon the bait. At Palm Beach,where 1000-1500h. Rainfall totals over 30 days prior no obviousconcentration oflarval habitats other to each collection were 43 mm for the first and than water-retaining plants occurred, the diur- 263 mm for the second.The Ndumu and Sku- nal, anthropophilic mosquitoeswere only col- kuza populations, known and assumed to be lected in small numbers at any one site. It was non-anthropophilic, respectively, had biting necessaryto move regularly over small distances rates Iower than 1 per man-hour even though to find fairly large numbers of these species they were prevalent in the bamboo pots (Table biting. 1). Fow Stegornylospecies other thanAe. aegypti Male mosquitoes subsequentlycaptured and were taken in the human-baited collections. identified as Ae. aegypti were often observedto Their averagebiting rates are shown in Table 3 swarm in small numbers (rarely greaterthan 10) together with the rate for Er. quinqu'euittatus. about the bait, a man's exposed leg and foot. Aedesdemeillnniwas found to bite readily during Within minutes of swarm-formation, the con- the midday period. The biting rates measuredin specific females arrived at the bait. They were 1991were 13 per man-hour at Armadale (collec- immediately approachedby the males and cop- tion effort : 4.2 man-hours between 1000 and ulation ensued in the air. Mating mosquitoes 1215h) and 38.8per man-hour at Palm Beach either remained.in copula in flight or landed on (collectioneffort: 1.7man-hours between 1155 the ground or on the bait to mate. The females and 1250h). Aedessimpsoni was only encoun- then approachedthe bait to feed. Female Ae. tered at high biting rates in Johannesburgin the aegyptiwere often slow to alight before feeding, late afternoon. Aedes strelitziae was the most particularly if a slight breezewas blowing. Males common anthropophilic species at Armadale, also alighted on the bait but apparently only to with biting rates ranging from 8.7 to L6.3 per rest, becauseas soon as femalesapproached, the man-hour, the higher obtained during 1000- males wouid up to meet them. Occasionally, 1215h (collectioneffort = 4.2 man-hours).Er- femalesarrived and fed on the bait without the etrnapoditesquin4ueuittaars was not commonly presenceof males in the vicinity. Similar behav- collectedas adults except for a site in Richards ior patterns were observed for Ae. derneillani Bay where the biting rate in December1989 was DECEMBER1991 DnNcup VEcroR EcoLocY 579

Table 3. Daytimehuman-baited collections at strelitziae and ,Er. quinqueuittatusare potential various localities; averagebiting rates of the most vectors of denguebecause of their domestic or prevalent speciesother than Aedesaegypti. peridomesticoccurrence. Each specieswill be Biting rate discussedin the aboveorder. (per man- Aedes aegypti: The adult mosquito can sur- Species hour) Locality vive under widely variable climatic conditions, Ae. (StS.)demeilloni 5.4 Palm Beach and anthropophilic populations occur in the 5.5 Armadale* southeasternCape Province at Grahamstown dendrophilus 0.1 St. Lucia Estuary (Edwards 1941; Jupp, unpublished data) and simpsoni 1.2 Palm Beach East London (Mattingly 1953; Kemp, unpub- 2.0 OsloBeach Iisheddata). both above33"S latitude. Further- 0.5 Park Rynie more, the speciesis representedby established O.2 Richards Bay populations at a variety of altitudes ranging 0.3 St. Lucia Estuary (Johannesburg) 7.5 Johannesburg from near sealevel to 1,800m 0.5 Skukuza in South Africa, mainly associatedwith wooded strelitziae 2.5 Palm Beach savannah ftushveld) and forest (coastal scrub. 9.6 Armadale* riverine and montane) or with the urban envi- 0.4 RichardsBay+* ronment (Muspratt 1956).This specieshas be- Er. quinqueuittatus 0.7 Palm Beach come adapted to a wide range of larval habitats 0.6 Stanger ranging from natural tree holes and leaf axils to 2.3 RichardsBay artificial containers in the domestic and peri- 0.2 Mtubatuba domesticenvironments (Hopkins 1952,Horsfall 0.9 St. Lucia Estuary 1955). * Collectioneffort : 15man-hours. ** The southernNatal coasthas beenurbanized Collectioneffort : 14man-hours. extensivelyto cater for the tourist industry, and the endemic populations of Ae. aegypti appear to have adaptedto utilize the peridomesticen- 10 per man-hour (collection effort = 2 man- vironment.These local populationswere shown hours in the Iate afternoon). to be highly anthropophilic (Table 2) and could No evidenceof the exotic species,Ae. albop- constitute a serious health hazard should they lcfus, was found in the courseof this survey, be found to be efficient vectors of dengue. In despitethe recentdiscovery of immaturesin tire northern Natal the urban are fewer casings imported from Southeast Asia and areas and less developed landedin CapeTown (Hunt et al. 1990). except for Richards Bay, an in- ternational harbor. High densitiesof anthropo- philic Ae. aegypti were not as evident in our DISCUSSION collections at these localities, although con- Our study has concentrated on particular tainer indices (Table 2) were significant at the areasof South Africa. First, thosewhere dengue collection sites which consistedmainly of tire is likely to be successfullyintroduced into the dumps. The collections at Ndumu, a relatively country via the shipping and tourist industries undevelopedgame reserve on the Mozambique and, second,where the most probablevectors, border, are consideredto representa non-an- the Stegornyiaand Diceromyio species,are to be thropophilic population of Ae. aegypti.Artificial found. The characteristics of potential vectors containers were not present at this locality. An are their appropriate distribution, abundance extensiveseries of human-baitedcollections in and anthropophilic behavior. If a speciesis a the reserve(Mclntosh et aI. t972) failed to dem- known vector of outside South onstrate Ae. aegypti in gallery forest dominated Africa, this is also an important consideration. by Ficussycamorus Linn. (Moraceae).This was Aedesaegypti andAe. furcifer arc denguevectors confirmed by the present adult collectionsat the elsewhere(Gubler 1988, Roche et al. 1983). same site, even though ovitraps yielded abun- Aedescordellieri must also be considered,even dant eggsof Ae. aegypti(Table 1). though its potential for denguetransmission is The Transvaal collectionsinclude anthropo- unknown. A dengue 2 epizootie in the Ivory philic populations ofAe. aegyptifrom Johannes- Coast and Upper Volta was associatedwith Ae. burg in the south and Tzaneen in the north. The furcifer and Ae. taylori (Cordellier et al. 1983). Johannesburgpopulation, however, is probably More recentlyHuang (1986a)has describedAe. not an establishedone, i.e., does not overwinter cordellieri, a third member of the Ae. furcifer there. At least some of the tires which formed group from the same region, and it is possible the larval habitats were imported via Durban, that this speciesmay have played a role in the and it is probable that Ae. aegypti eggs were epizootic. Aedes derneilloni, Ae. simpsoni, Ae. introdueed with the tires. The relevant site was 580 JouRNlr,or rns AN{nRrcANMoseurro Contnol Assocrerron VoL. 7, No. 4 on the grounds of a small business concern South Africa are thus comparable to those re- which reprocessedthe rubber from tires into ported from East Africa. The occurrence of a commercialgoods, e.g., sandals. This illustrates highly anthropophilic, peridomestic population the unusualmode ofrange extensionin the form in the metropolis of Durban is potentially very of eggsbeing dispersedby the usedtire industry, important in terms of epidemiology. not only intercontinentallyas in the caseofAe. Aedesfurcifer: Our study was not designedto albopictus,butfrom the subtropicalregion where sampleadults of this species,which is primarily the speciesis endemic to the temperate region nocturnal with a crepuscular activity peak just which can support the speciesduring the sum- after sunset (Port and Wilkes 1979).The Ae. mer in South Africa. furcifer group was previously thought to be con- Egg collections were made at a farm in the fined to the tropical regions with the southern- Magaliesbergmountains, Skukuza in the Kruger most distribution being in the region of Lake St. National Park and a game farm near Mica to Lucia (28"S latitude) on the 18"C midwinter samplewhat were consideredto be non-anthro- isotherm (Jupp and Mclntosh L988).Aedes fur- pophilic populations due to their feral nature. cifer sensu strictu was found in the ovitraps Limited human-baited collections at the Magal- placed in a horticultural nursery in the suburb iesberg Iocality proved negative for Ae. oegypti of Congellain Durban at 29'53'5 latitude (Table and more extensive collections at Skukuza 1). However,the abundanceof the mosquitoin yielded few adults, in spite of the presence of the bamboo pots was low and the epidemiologi- the speciesin ovitraps at both localities. Sku- cal threat may consequentlybe slight. Sizable kuza, paradoxically, is an urban Iocality in a populations only occur after heavysummer rain- gamereserve and consistsofa largestaffvillage fall in the often drier woodedsavanna of north- associatedwith an industrial site (workshops ern Natal and the northeasternTransvaal (Jupp and Iight industry) and tourist camp. The Mica and Mclntosh 1988).Because it hasbeen estab- locality in the wooded savanna region of the lished as a vector of dengue in West Africa northeastern Transvaal yielded collections of (Cordellier et al. 1983),it must be regardedas a Ae. aegypti in ovitraps. Human-baited collec- potential vector in the tropical regions of South tions were not attempted, as an earlier study Africa. (Jupp and Mclntosh 1990) described the non- Aedescordellieri: As for the previous species, anthropophilic nature of the population. experimental design precluded the collection of The strong diurnal pattern in the biting activ- adults of the nocturnally active Ae. cordellieri. ity of Ae. aegypti is well known. However, the It was present during the rural epidemicat Mica possibilityof biting peaksjust after sunriseand (Mclntosh et al. t977), being identified then as just before sunset was indicated by the work of Ae. taylori. It constituted about l% of the Ae. Reed and colleaguesin 1901 (seeHorsfall 1955) furcifer/ cordellieri total basedon the proportion and that of Trpis et al. (1973).This was the of males collected(Jupp and Mclntosh 1990). basisfor the timing of our human-baitedcollec- This specieswas representedin the ovitraps in tions. There is also strong evidencethat major the tropical region in association with Ae. fur- biting peaks exist in the hour before midday cifer (Table 1). The abundancein the bamboo (Teesdale1959) and from 1200to 1400 h and pots appearedto be too low for the speciesto be during the crepuscularperiods (Lumsden 1957). considered epidemiologically important, even Biting activity during the daytime hours outside though it must be considereda potential vector of our standard periods was demonstratedin the of denguedue to its taxonomic and behavioral present study: the Durban and Palm Beachpop- similarity to Ae. furcifer. ulations of Ae. aegypti were collected from 1000 Aedesdemeilloni: This speciesis limited to to 1500h at very high biting rates. the eastern coastal plain largely due to special Twenty-four-hour human-baited collections habitat requirements.The leaf axils and apical yielded biting rates for Ae. aegypti of up to 13.4 crown of the plant, Dracaena hookeriana,form per man-hour during the 1952-53epidemic of the natural breeding places (Muspratt 1956). fever in (Lumsden Even though Ae. demeilloni was found in bam- 1955).Trpis et al. (1973)made extensive record- boo pots and sometimesin artificial containers ings of landing rates on man for the speciesin on the south coast of Natal, these populations an automobile dump in Dar-es-Salaam,Tanza- appearto be dependenton the presenceof large nia. The landing rate is an approximation of stands of Dracaena spp. Aedes demeilloni is a biting rate, and if one extracts their data for highly anthropophilic species,as the 1991 col- periods in the day corresponding to the times Iection at Palm Beach shows. Muspratt (1956) when our collectionswere made, a rate of 9.9 reports biting rates of 30-50 per man-hour fur- per man-hour is obtained. The biting rates for ther south at Port St. Johns on the Transkei the anthropophilic populations of Ae. aegypti in coast. It must be considereda potential vector, Dncpvsnn DnNcup Vpc'ron Ecolocv as its restricted distribution coincides with the ture. Lounibos (1980)found that Er. subsimpli- denselypopulated Natal coast. crpesis common in and Er. quinqueuittatus ab' Aedes simpsoni: Its similarity to Ae. aegypti sent from the fruit husks of the Loganiaceaein in distribution and ecology strongly suggests (Lounibos1978, 1980). We foundjust the that this species is a potential vector. Aedes opposite with apparently monospecific collec- simpsoniis commonthroughout the tropical and tions of Er. quinqueuittatus occttrring in fruit subtropical regions of South Africa (Table 1) husks of Strychnos madagascariensisat St. Lu- and is highly prevalent throughout its range, cia Estuary. With respect to larval predation, utilizing natural and artificial larval niches in a Hartberg and Gerberg(1971) report no evidence variety of environments including the feral (tree of cannibalism for the speciesin the laboratory, holes),agricultural (commercial banana planta- although Haddow (1946)describes larvae from tions) and domestic (Muspratt 1956, Huang Ugandaas predatory.Lounibos (1980)suggests 1986b). It is diurnally active (Muspratt 1956) that, unlike Er. siluestrisIngram and de Meillon and bites man readily (Table 3). North and East and Er. subsim.plicipes,it is not able to develop African records of its biting rate in human- beyond the third instar on a predatory diet baitedcollections and its vectorcompetence are alone. open to question after the taxonomic revision of In Natal, Er. quinqueuittatus has become the Ae. sirnpsonigroup by Huang (1986a,1986b). adaptedto both natural and artificial small re- Aedessirnpsoni was describedas a major vector ceptaclesfor its larval habitat. Furthermore, it of yellowfever in (Leeand Moore 1972), is closely associatedwith man in the domestic in (Gillett 1969) and in East Africa environment, has a diurnal biting-activity pat- (Hamonet al. 1971),but Huang (1986b)suggests tern and is significantlyanthropophilic. Conse- that this work relates to Ae. bromeliae; appar- quently, it must be regardedas a potential vector ently Ae. simpsoni is confined to southern Af- of dengue. rica. It may be concluded that of the 7 species "Ihe Aedes strelitziae: preferred oviposition identified as potential vectors of dengue in site ofthis speciesis in the leafaxils of Strelitzia South Africa, five are potentially epidemic vec- nicolai,a commonplant on the Natal coastand tors. The 5 speciesfall into 2 groups according in montane and riverine forests further inland to our ecologicalcriteria for selection.The most (Muspratt 1956).This plant is much more prev- important group comprises Ae. aegypti, Ae. alent than Dracaena hookeriana.Only in a few simpsoniand Er. quinqueuittatusbecause of the localities and at Iow abundancedid Ae. strelitziae prevalenceof these speciesand their closeas- oviposit in bamboo pots (Table L). Artificial sociationwith man in the urban environment. containers were also used to some extent but The secondgroup consistsof Ae. demeilloni and only when associatedwith large stands of Stre- Ae. strelitziae which are regardedas less impor- litzia nicolai. This dependenceon a particular tant because of their dependenceon specific plant introduces restrictions on geographicdis- plants for their larval habitats, which limits tribution, but Ae. strelitziae still exists in close their distribution. The 2 remainingspecies, Ae. proximity to large human populations on the furcifer and Ae. cordellieri, are essentially rural Natal seaboard and is highly anthropophilic specieslimited to the tropical region. Therefore, (Table 3). although they are both probably competentvec- Eretmapodites quinqueuittatus: This species tors, they are unlikely to becomeinvolved in appearedto be the only member of the genusto epidemictransmission. occur in abundancein the study area. The ovi- position requirements almost always involved ACKNOWLEDGMENTS small collections of rainwater in discardedtins and cardboardcartons (milk and local beer). One of us (P.G.J.) acknowledgesgrants to- Muspratt (1955) confirms these breeding re- ward this project from the Poliomyelitis Re- quirements and indicates that natural collec- searchFoundation and the South African Med- tions of rainwater in fallen leaves,snail shells ical Research Council. We are grateful to the and leaf axils are also utilized. The facility with Directors of the National Parks Board, the Kwa which the speciesutilizes such small receptacles Zulu Bureau of Natural Resourcesand the Natal is apparently augmentedby its larval behavior, Parks Board for permission to work in areas including the ability for facultative cannibalism under their jurisdiction. We thank staff of the and larval activity out of the water (Hopkins Arbovirus Unit for technical assistance. Our 1952),both of which were observedin our labo- gratitude for hospitality and field collaboration "Armadale," ratory. is extended to: J. Henderson of Some inconsistencieswith respectto larval Port Shepstone;P. Volschenkand T. B. Wessels requirementsand behavior exist in the litera- of the Department of Community Services, 582 JounNer,or rHs AN,rsRrceNMoseurro CoNrRor, Assocrerror.r VoL.7,No.4

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