Experimental and molecular genetic analysis of the impact of pyrethroid and non-pyrethroid insecticide impregnated bednets for mosquito control in anarea of pyrethroid resistance

Experimental huts in Cote d'Ivoire were used to evaluate the pyrethroid alp ha-cypermethrin, the non-ester pyrethroid etofenprox, the organophosphate p irimiphos-methyl and the carbamate carbosulfan on bednets against pyrethroi d-resistant Anopheles gambiae Giles. To test for selection for the resistan ce gene by the treated nets, A. gambiae collected live or dead from the hut s were kept and analysed for the presence of the kdr gene using a new polym erase chain reaction followed by sequence-specific oligonucleotide probing (PCR-SSOP) for kdr-genotyping. Deliberately holed bednets freshly treated w ith pirimiphos-methyl or carbosulfan caused over 90% kill of A. gambiae s.s . and Culex spp. However, the mortality with alpha-cypermethrin or etofenpr ox treated nets was similar to that with untreated nets. Bloodfeeding of A. gambiae s.s. on the sleepers under the nets was only significantly reduced by alpha-cypermethrin and carbosulfan. Tests of the residual activity of t he bednets after seven months showed that pirimiphos-methyl had lost its ef ficacy while carbosulfan still performed well. Once again the pyrethroid tr eated nets gave similar results to the untreated nets. Selection for the kd r-allele by alpha-cypermethrin and etofenprox, but not by carbosulfan, was indicated by PCR-SSOP genotyping of mosquitoes. Thus carbamates such as car bosulfan, or organophosphates of longer persistence than pirimiphos-methyl and of low mammalian toxicity, would seem to be a promising alternative to be used on bednets, particularly in areas of pyrethroid resistance.