Permethrin-impregnated bednets: behavioural and killing effects on mosquitoes.

Permethrin-treated pieces of netting and simulated bednets were evaluated against Anopheles gambiae Giles and Aedes aegypti (L.) in the laboratory. When female mosquitoes were allowed to feed on a human arm through pieces of impregnated netting fastened at the end of tubes, doses above 2 g/m2 were required to stop blood-feeding of both An. gambiae and Ae. aegypti. A much lower dose prevented Ae. aegypti from feeding on mice through impregnated netting. When mosquitoes were released in a room and a human subject sat under a permethrin-impregnated (0.2 g/m2) bednet with an arm pressed against the net (mesh 1.5 mm), mosquitoes failed to bite through the net. All the mosquitoes trying to bite through or entering the net through holes cut in it were knocked down within 30 min of release and ultimately died. Permethrin-impregnated wide-mesh (4 or 8 mm) bednets similarly prevented entry and caused high mortality-rates of An. gambiae.