Reduced susceptibility of Anopheles gambiae to permethrin associated with the use of permethrin‐impregnated bednets and curtains in Kenya

Abstract. Susceptibility of the malaria vector Anopheles gambiae to permethrin decreased following the installation of mosquito nets impregnated with 0.5 g permethrin per square metre in four villages near Kisumu, Kenya. During the first year that permethrin‐impregnated bednets and curtains were in place, the exposure time to 50% mortality (LT 50 ) increased 2.5‐fold from 13 to 33min, while the LT 5() for An.gambiae was unchanged in two other villages where no intervention measures were used. Two years after permethrin‐impregnated mosquito nets were distributed the LT 50 s for An.gambiae were 28, 28 and 16min, respectively, in the villages with bednets, curtains and with no such intervention. Using a colony of An.gambiae derived from females collected in the villages using permethrin‐impregnated moquito nets, we lengthened the LT 5n from 28 to 41 min in two generations by exposing all females to permethrin‐treated papers for 60 min and rearing offspring of the survivors. Permethrin‐impregnated bednets and curtains are intended to reduce vectorial capacity. Reduced susceptibility to permethrin could counter this beneficial effect.