Experimental hut comparisons of nets treated with carbamate or pyrethroid insecticides, washed or unwashed, against pyrethroid‐resistant mosquitoes

Abstract

<jats:p><jats:bold>Abstract. </jats:bold> The efficacy against mosquitoes (Diptera: Culicidae) of a bednet treated with carbamate insecticide [carbosulfan capsule suspension (CS) 200 mg/m<jats:sup>2</jats:sup>] was compared with four types of pyrethroid‐treated nets in veranda‐trap huts at Yaokoffikro near Bouaké, Côte d'Ivoire, where the malaria vector <jats:italic>Anopheles gambiae</jats:italic> Giles carries the <jats:italic>kdr</jats:italic> gene (conferring pyrethroid resistance) at high frequency and <jats:italic>Culex quinquefasciatus</jats:italic> Say is also pyrethroid resistant. Pyrethroids compared were lambdacyhalothrin CS 18 mg/m<jats:sup>2</jats:sup>, alphacypermethrin water dispersible granules (WG) 20 mg/m<jats:sup>2</jats:sup>, deltamethrin 50 mg/m<jats:sup>2</jats:sup> (Permanet™) and permethrin emulsifiable concentrate (EC) 500 mg/m<jats:sup>2</jats:sup>. Insecticidal power and personal protection from mosquito bites were assessed before and after the nets were used for 8 months and hand washed five times in cold soapy water. Before washing, all treatments except permethrin significantly reduced blood‐feeding and all had significant insecticidal activity against <jats:italic>An. gambiae</jats:italic>. The carbosulfan net gave significantly higher killing of <jats:italic>An. gambiae</jats:italic> than all pyrethroid treatments except the Permanet. Against <jats:italic>Culex</jats:italic> spp., carbosulfan was more insecticidal and gave a significantly better protective effect than any of the pyrethroid treatments. After washing, treated nets retained various degrees of efficacy against both mosquito genera – but least for the carbosulfan net. Washed nets with three types of pyrethroid treatment (alphacypermethrin, lambdacyhalothrin, permethrin) gave significantly higher mortality rates of <jats:italic>Culex</jats:italic> than in huts with the same pyrethroid‐treated nets before washing. After five washes, the Permanet™, which is sold as a long‐lasting insecticidal product, performed no better than the other nets in our experimental conditions.</jats:p>