84 JouRNer,oF THE AunRrceN Mosqurro Conrnor,Assocrertow VoL. 8, No. 1

EFFICACY OF PERMETHRIN- AND CYPHENOTHRIN- IMPREGNATED NETTINGS AGAINST CUiNi-Pli'rcXS PALLENS

TAKAAKI ITOH1 INn TAKESHI KURIHARA,

ABSTRACT' Laboratory tests were conductedto determine the effect of different bed impregnatedwith permethrin net materials, or.clphenothri n, on Culcx mosquitoes., and vinylon nettings were more efficaciousthan or nvlon.

on mosquito .Research bed nets impregnated the caseof the cotton netting, O.l2b and 0.2b% with a-ninsecticide, as a meansof self-protlection concentrationswere employed,as the amount of from bites mosquitoes _of has been reported. diluted solution absorbedwas larger than that H-ossainand Curtis (1989)compared the &fi.acy of other nettings. of permethrin treated and cotton nettings For chemical analysis, a 5 x 5 cm piece of the against Anophclesgambiae Giles and Aedes i- netting was used.This was extracted gypti (Linn.) with 20 ml in the laboratory. They observed of acetone solution containing an appropriate that 2.5 g/m2 permethrin of on nylon and 5.0 g/ amount of diphenyl phtalate as an iniernaL m' oncotton was required to prevent mosquitoes standard of permethrin and cyphenothrin. The from biting a human arm. Lines et al. ?rg8Z) extract was shaken for 10 min. The quantity of also examined the efficacy of permethrin-im- active ingredient was determined gas pregnated by cirro- nylon and cotton nettings, in a win- matography using a Simadzu GC-7A apparatus dow trap in an experimental hut in Tanzania. equipped with a flame ion detector. column of to determine the effect of the treated netting on 5% SE-30on uniport HP (100-200mesh) 1.1m feeding and survival of An. gambiae and-An. long, temperature of injection port at 280"C and funestus Giles. Their results indicated that cot- oven at 240"C,nitrogen carrier gasat b0 ml/min tort netting was not as effective as nylon netting. flow, air flame at 0.6 kg/m'and hydrogenat 0.g The important consideration for bed nets im- kg/m'. The analyseswere replicated2 times. pregnated with insecticides is the makeup of Bioassays were performed as follows: the their woven materials. We investigated the ef- treated netting was fastenedto a plywood panel fect permethrin- of and cyphenothrin-impreg- with drawing pins. A plastic petri dish (0.T cm nated on various netting materials on Culex deep x 3 cm diam) with a 1 cm center hole. was mosquitoes.The impregnatednetting was chem- placed upside down on the netting. Ten 3-4 day ically analyzed to determine the amount of ac- unfed adult female Cx.pipiens pallens Coq. weie tive ingredient on the netting and its biological introduced into the petri dish through the ienter effect on the mosquitoes. hole and allowed to contact the netting for 20 . Permethrin (3-(phenoxyphenol) methyl minutes. Following exposure, the mosquitoes ( -cis,trans-3- -2 1RS ) (2 dichloroethenyl) -2,2- di- were transferred to a polyethylene cup and were methyl cyclopropanecarboxylate,cis/trans ratio provided with a cotton plug soakedin aE% sugar 44/ 56, purit y 95.6Vo)and cyphenothrin ( (RS) -d- solution. Mortality was observedafter 24 hours. cyano-3-phenoxybenzyl(1R)-cis, trans-chry- The experiment was replicated B times. santhemate,purity 98.5%, Sumitomo Chemical Table 2 shows the results of the chemical Co., Ltd., Osaka) were formulated into emulsi- analysis of the treated nettings. Since the mesh fiable concentrates with an emulsifier (Sorpol size and thickness of the threads were quite SM 200, Toho Chemical,Tokyo) and a xylene different, the amount of active ingredient was solvent, 10:10:80w/w. Nettings made of cotton, expressedas ppm to the weight of the netting, polyethylene, polyester, nylon and a mixture of instead of mg/m". With the exception of cotton cotton and synthetic (Vinylon, Kurare Co. Ltd., Tokyo) were used and their characteristics are shown in Table 1. Piecesof netting, 10 x 10 f"tt" t.Ch"t".t"rlW cm were immersed in a water diluted emulsific- ableconcentrate of.0.25,0.b and 1.0%for b min Mesh Thicknessof Weight and dried at room temperature for 24 hours. In Material size** thread(mm) (g/m,) Cotton Irregular 0.16 35.0 Polyethylene 16 0.36 LDt).2 I Takarazuka ResearchCenter, Sumitomo Chemi- Polyester 90 0.08 27.0 cal Co. Ltd., 4-2-1, Takatsukasa,Takarazuka, Hyogo Nylon 14 0.26 50.7 665,Japan. Vinylon* 22 0.24 37.8 2 Teikyo University School of Medicine. Itabashi. * A mixture of cotton and svnthetic fiber. Tokyo 173,Japan. ** Threads per inch. MARCH 1992 OpnnetroNlt AND SCIENTIFIcNorEs 85

Table 2. Absorption of permethrin and cyphenothrin Table 3. Efficacy of permethrin and cyphenothrin on onto various nettings. various nettings againstCulex pipiens pallens.

Concentration of treatment Concentration of treatment o.25% 05% r.o% Material 0.25% 05% r.0% Cyphenothrin Cyphenothrin Cotton* 8,237ppm 11,597ppm - ppm Cotton* 43 Polyethylene 497 1,288 2,843 Polyethylene 100 100 tt0 Polyester 1,802 3,77r 5,647 Polyester 100 100 100 Nylon 2,678 4,969 10,841 Nylon oo 90 100 Vinylon 2,468 5,2r4 tL,444 Vinylon 100 100 100 Permethrin Permethrin Cotton* 5,759ppm 20,742ppm - ppm Cotton* 28 Polyethylene r,240 1,456 3,817 Polyethylene 100 100 r.00 Polyester 3,192 4,547 9,202 Polyester 100 100 t00 Nylon 2,496 7,463 9,581 Nylon 32 48 /o Vinylon 3,579 8,541 9,358 Vinylon 100 100 100 * The concentrationstreated were 50Vo of indicated * The concentrationstreated were 50% of indicated values. values, +* Percent mortality, based upon the averageof 3 replicates.Cotton netting was used as untreated net- netting, the amount of cyphenothrin absorbed ting and 0% mortality was obtained. on the threads generally depended on the concentration. Permethrin was not as much af- fected by concentration. Cotton netting ab- their biological efficacy. He concluded that in- sorbedthe largest amount and polyethylene net- secticides are less available to the insects on ting the smallest amount of insecticides.There cotton thread than on because of were only small differences in the amount ab- the apparently greater and deeper absorption of sorbedby the polyester, nylon and vinylon net- the cotton . However, Snow et al. (1987) tings, though the amount of cyphenothrin ab- pointed out that insecticides on netting are con- sorbed by the polyester netting was slightly centrated on a far smaller area of frber than on Iower than that of nylon and vinylon nettings. sheet nets and can be expected to be more effec- Table 3 showsthe efficacy of permethrin and tive. Additional studies should be carried out cyphenothrin at various concentrations on var- comparing netting of the same size and thread ious types of nettings against Cx.pipiens pallens. thickness. Although cotton netting absorbed the largest The authors thank Dr. E. J. Gerberg for his amount of both insecticides,its efficacy was less critical review of this manuscript. than that of polyethylene, which absorbedthe least amount. The efficacy of each insecticide REFERENCES CITED that on polyethylene, on nylon was inferior to Hossain,M. I. and C. F. Curtis. 1989.Permethrin- even though nylon netting absorbed a larger impregnatedbednets: behavioural and killing effects amount ofinsecticide than did the polyethylene. on mosquitoes.Med. Vet. Entomol. 3:367-376. These results suggestthat polyethylene as a bed Lines, J. D., J. Myamba and C. F. Curtis. 1987.Ex- net material can be expectedto be more effrca- perinental hut trials of permethrin-impregnated cious at a low concentration. mosquito nets and eave curtains against malaria Hossain and Curtis (1989) and Lines et al. vector in Tanzania. Med. Vet. Entomol. 1:37-51. (1987) both reported that permethrin-impreg- Rozendaal,J. A. 1989.Impregnated mosquito nets and nated nylon nets were more effective than cot- curtains for self-protectionand vector control. Trop. mosquitoes.The Dis. BuIl. 86:1-41. ton-impregrrated nets against Snow. R. W.. M. Jawara and C. F. Curtis. 1987. comparativeefficacy of nylon treated netting to Observationson Arnphelesgambiae Giles, s.l. (Dip- that of cotton in this study reconfirms their tera: Culicidae) during a trial of permethrin-treated observations. Rozendaal (1989) discussed the bednetsin The Gambia.Bull. Entomol.Res.77:279- influence that the bed net fiber material had on 286.