Journal of the American Mosquito Control Association,9(4):414-420, lgg3 Copyright @ 1993 by the American Mosquito Control Association, Inc. ASSESSMENT OF THE RESIDUAL EFFICACY OF LAMBDA-CYHALOTHRIN 2. A COMPARISON WITH DDT FOR THE INTRADOMICILIARY CONTROL OF ANOPHELES ARABIENSIS IN SOUTH AFRICA B'L' SHARP"" I-TKEGlti{3t";Xfff*f1"!' F BREDENKAMP"

ABSTRACT. There are several factors that support the need to assessthe efrcacy ofpotential alternative insecticidesto DDT for malaria vector control. The objectivesof this study wereto evaluatethe persistence and efrcacy against Anopheles arabiensis oflambda-cyhalothrin used as an intradomiciliary insecticide in daub huts and to compare its efrcacy in this regard to DDT. Exit trap catches showed the population of An. arabiensrs was high during the months of January to March, with a peak in February. During all months, the number caught leaving lamMa-cyhalothrin-sprayed huts was markedly less than the number from both control and DDT-sprayed huts. The p€rcentage surnival ofbloodfed mosquitoes ranged from a low of 55% caught leaving the lambda-cyhalothrin-sprayed huts, to 82% ofthose caught leaving DDT- sprayedhuts. The percentageofbloodfed mosquitoescaught leaving huts was high (>60%). The survival of unfed mosquitoeswas low, even from the control huts (43%).

INTRODUCTION international research funding agencies will no longer fund research in any way associated with Anopheles arabiensis Patton is the primary DDT. 3) Researchon DDT levels in men and vector of malaria in many parts of Africa (White women in the endemic area of northern Natal/ 1974). This member of the Anophelesgambiae KwaZulu showed 20 x the adult dietary intake complex predominatesin malaria endemic areas overall in the study and 3l x the adult dietary of northern Natal Province and KwaZulu, South intake in primiparous mothers (Bouwman et al. Africa, and throughout southern Africa (Shelley I 990). 4) Sharpet al. ( I 990) showedthat the hut- 1973,le Sueurand Sharp1988, Sharp et al. 1990, leaving behavior of An. arabiensishamperedthe Sharp and le Sueur l99l). Control of adult ma- control of this speciesby intradomiciliary DDT laria vectors was started in the Natal Province spraying.5) The spreadofchloroquine- and mul- of South Africa in 1931, with the use of intra- ti-resistant Plasmodium malaria in domiciliary pyrethrum spray (Park Ross 1936). falciparum southern Africa places an increasing emphasis Residualhouse sprayingwith DDT was firstused on the need for more efficient vector control in 1948and by 1958all homesteadsin the ma- (Freeseet al. 1988, 1991;Schapira 1990). larious areas were subject to the annual appli- The above factors justit the present assess- cation of 75% w.w. DDT at2.5 g/mz. Currently ment of a suitable alternative to DDT should no evidenceexists of DDT resistanceby any spe- such a need for more emcient vector control arise. An. gambiae complex in these areas cies of the I-ambda-cyhalothrin, a biodegradable synthetic (Sharpet al. 1990). pyrethroid, recently passedthrough all phasesof The efficacy of potential alternative insecti- the World Health Organization (WHO) Pesticide DDT for malaria vector control in South cidesto EvaluationScheme (WHO 1990a,1990b, l99l). Africa should be assessedbecause of the follow- Both laboratory and field trials have shown that ing factors: l) It is generally accepted that agri- lambda-cyhalothrin as both an ultra-low volume pesticide use associatedwith large scale cultural (ULV) spray and a contact insecticide was highly irrigation projects exacerbates the agricultural eflectivein the control ofmosquito species(Rob- of insecticide resistance in mos- development erts et al. 1984, Schaeferet al. 1990, Miller et al. quitoes. A project ofthis nature has been initi- 1991, Sulaimanet al. 1991, Weathersbeeet al. ated in the malaria area of northern Natal/ I 99l). KwaZulu. 2) Social attitudes against the use of The objectives of this study were to evaluate DDT have increased to the degree that certain the persistence and efrcacy of lambda-cyhalo- insecticide in ' thrin used as an intradomiciliary National Malaria Research Programme, National daub huts against An. arabiensis and its eftcacy P. O. Box 17120, Congella 4013 ResearchCouncil, as compared to DDT. South Africa. 2 KwaZulu Health Department, Private Bag X002, Jozini 3969 South Africa. MATERIALS AND METHODS 3 Center for Epidemiological Research of South Af- rica, National Research Council, P. O. Box 17120, The study was carried out at 2 localities, Mam- Congella4013 South Africa. fene (27"23'5, 36"16'E), Ubombo District, and 414

4t7 DscErrBER1993 Ir.r-ruporncrnnv Coxrnol oF ANoPHEI'ESARABIENSIS

The suryival of An. gambiae s./. caught leaving 50 huts varied depending on blood meal status of the mosquitoes and depending on the insecticide 39.25 status ofthe hut (Table 2).Tble percentagesur- vival of bloodfed mosquitoes ranged from a low of 559o caught leaving the lambda-cyhalothrin- o sprayedhuts to 8206ofthose caught leaving DDT- E'o sprayed huts. The percentageof bloodfed mos- E quitoes caught leaving huts was hieh (>60%). The survival of unfed mosquitoes was low, even f;, from the control huts (43%). There was no sig- 11.06 10.ff nificant difference in the survival of unfed mos- quitoes between the huts ofdifferent status (P > 3.67 0.05). In respect to bloodfed mosquitoes, there was a significant difference between the control and the DDT-sprayed huts (P: 0.006), and be- JAl{ FEB ilAR APR IIAY tween the DDT- and lambda-cyhalothrin-sprayed Fig. 2. Monthly ratio (lambda-cyhalothrin huts (P < 0.001), but not between the control UCONoI:DDT) of Anophelesgambiae s./. caught and lambda-cyhalothrin-sprayed huts (P > 0.05). leavingDDT- andlambda-cyhalothrin-sprayed huts at In both the DDT and the control huts there was Mamfenearea. a significant difference in the survival ofbloodfed vs. unfed mosquitoes(P < 0.002). Dosagemor- the data presented are considered to reflect the tality regressions showed no DDT or lambda- behavior of An. arabiensis. cyhalothrin resistance in the population at dis- The fed:gravid ratios ofthe exit trap-caught criminating dosagesof 4.0% DDT and O.O25% mosquitoes from lambda-cyhalothrin-sprayed, lambda-cyhalothrin. DDT-sprayed, and control huts (7.4:1, ll.7:1, 22.5:l)were considerablyhieherthan thosefound previously for An. arabiensis resting indoors in DISCUSSION control huts (1.4:1-3.9:l) (Shelley1973, Sharp Two study sites were chosen, one in the Ndu- et d. I 990). Thesehigher ratios ofexit trap-caught mo area of Ingwavuma District and the second mosquitoes are in keeping urith the exit trap data at Mamfene in the Ubombo District, to optimize ofSharp et al. (1990) and are indicative ofhut the chancesofobtaining a population ofl n. ara- leaingby An, arabiensis after feeding. The blood biensis ofa suitable size to carry out the study. meal statusesofthe hut-leaving mosquitoes from Only the population at Mamfene was of a suit- control, lambda-cyhalothrin-, and DDT-sprayed able size for investigation. huts in the present study were very similar to The use of the Miles (1979) key and nonspe- one another (Table l), with the highest percent- cific esterases(Mahon et al. 1976) for the elec- age being bloodfed, followed by unfeds, and a trophoretic identification of An. arabienslsfrom low number of gravids. These data compare well this areahas been verified chromosomally(Sharp with those found by Sharp et al. (1990) from et al. 1990).Using theseisoenzyme systems, 722 control huts, but the percentageofbloodffis from An. gambiae s./. were identified from both the both the lambda-cyhalothrin- and DDT-sprayed Ndumo and the Mamfene areas. All 55 speci- huts in this study were higher than that found mens identified from the Ndumo areawere An- for DDT-sprayed huts by Sharp et al. (1990). The arabiensis. relatively lower percentage of bloodfed mosqui- Botb An. arabiensis and An. quadriannulatw toes caught leaving DDT-sprayed huts (Sharp et were caught leaving huts at Mamfene.,4nopheles d. 1990) was previously interpreted as an indi- arabiensis was, however, the dominant species cation of irritancy by the DDT (Muirhead- (>98o/o),as was also found during the 1986-88 Thomson 1960), but the high percentagesof period by Sharp et d. (1990). As a consequence, bloodfeds from both the DDT- and lambda-cy-

Table l. Number of exit traps fitted, number of Anophelesgambiae s./. caught, and their blood meal status. Percentage Number of lz. Exit traps Bloodfed Gravid Unfed gambiae s.l. fitted DDT 67.2 5.7 27.O 1,013 269 Control 63.2 2.8 34.O 250 66 Lambda-cyhalothrin 63.8 8.6 27.5 58 147 418 Jounxll or rns AN,rBnrcewMosqurro Coxrnor, AssocrarroN Vor. 9, No.4

Table2. Percentagesurvival and percentagebloodfed of Anophelesgambiae s./. caught leaving control,DDT-, and lambda-cyhalothrin-sprayedhuts. Number Percent Percent survival Statusofhut Huts Mosquitoes bloodfed Bloodfed Unfed Overall Control 24 159 68.5 7l 43 63 DDT 139 998 64.0 82 38 68 Lambda-cyhalothrin 36 105 61.0 55 49 52

halothrin-sprayed huts in this study do not sub- leaving DDT-sprayed huts than lambda-cyhalo- stantiate this. thrin-sprayed huts. Control in lambda-cyhalo- Sharp et al. (1990) found that 72.9o/oof the thrin-sprayed huts exceededthat in DDT-sprayed bloodfedln. arabiensiscauglrt leaving huts were huts during each of the 5 months of the study surviving and this constituted26.2-31.5o/oof the (Fig. l). During January lambda-cyhalotlrin exiting mosquitoes.The resultsof this study con- showed <39 times better control than DDT. The firm the high survival of bloodfeds in that 820/o exit traps were fitted in January 2 wk after spray- of the bloodfed An. arabiensis caught leaving ing with lambda-cyhalothrin and this marked dif- DDT-sprayed huts survived (Table 2). The sur- ference may in part have been due to a fumigant ival of An. arabiensis caught leaving lambda- effect (Fig. 2) or extreme toxicity of the insecti- cyhalothrin-sprayedhuts was, however, lower at cide resulting in only very limited contact being 55o/o. necessary. The proportion of the mosquitoes that were The monthly population relative abundance, bloodfed and caught leaving DDT-sprayed huts determined as the mean number of An. arabien- (64%) was considerable higher than that found sls caught leaving per hut per night, sva5highest previously (26.2-31.5o/o). The percentagethat had during February and March and showed a dra- fed on humans (human blood index : 97.8o/o) matic reduction during April and May (Fig. l). and caught leaving huts was far higher than that Malaria transmission is seasonalin the endemic found in a previous study in the area (human malaria area of northern NataVKwaZulu with blood index : 66.80/0)(Sharp and le Sueur 1991). more than 70%ioof reported casesoccurring from Of 184blood mealsanalyzed from An. arabiensis, Januaryto May (Sharpet al. 1988).Bioassays on 49.4o/owere collected from homesteadsthat had hut walls showed lambda-cyhalothrin to be ef- a cattle kraal within 20 m. This is in keepingwith fective in killing An. arabienslsfor the duration the finding of Sharp and le Sueur ( I 99 I ) that the of the study period (January-May) in both the presenceof a cattle kraal closeto the homestead Mamfene and the Ndumo area. did not appear to affect the human blood index A hlgh level of DDT resistance exists in the of exit trap-caught mosquitoes. bedbug Cimex lectularius Linn. in northern Na- The bioassay results from both DDT- and laVKwaZulu allowing infestations to thrive in lambda-cyhalothrin-sprayed huts indicate that the DDT-sprayed huts (Newberry and Jansen indoor resting on the inner surfacesofthe huts 1986).These high infestations lead the residents would not have been possible for the duration to replaster the walls ofthe huts to cover bed bug of the study period. This conclusion conforms harborages,thereby effectively covering the DDT with the frndings of Sharp et al. (1990) that in- and reducing vector control (Newberry et al. 1987, door resting,/survivalwas not occurring in DDT- Sharp et al. 1990). Laboratory studies on lamb- sprayedhuts. da-cyhalothrin have shown this insecticide to be Dose mortality curves showed no increased highly effective in killing bedbugs (le Sueur et al. vigor tolerance or physiological resistanceto DDT 1994) and its use would reduce the need for re- or lambda-cyhalothrin in the wild ln. arabiensis plastering. relative to WHO standards,indicating that lim- The laboratorystudy by le Sueuret al. (1993) ited contact had occurred by the exit trap-caught showed a markedly reduced residual effect of An. arabiensrJwith the residual insecticides. lambda-cyhalothrin on mud substrates from the Control of An. arabiensisas measuredby the Tetepan and Mfekayi areasofl(waZulu. Organo- mean number of An. arabiensis caught leaving phosphatesand carbamates also showed reduced control, DDT-, and lambda-cyhalothrin-sprayed effectivenessin the latter area (K. Newberry, per- huts was significantly better in the lamMa-cy- sonal communication). These data emphasizethe halothrin-sprayed huts than in the DDT-sprayed need for area-specific investigations when con- huts. Over the 5-month study period (January- sidering alternative insecticides that are less sta- May), 9. 5 tirnes more ,4n. arabiensis were caught ble than the traditionally used organochlorines.