THE EFFECT OF PERMETHRIN-IMPREGNATED BEDNETS ON HOUSE ENTRY BY MOSQUITOS (DIPTERA, CULICIDAE) IN THE GAMBIA

A trial was carried out using experimental huts to determine whether mosquitoes deterred from entering a building where a person slept under a permethrin-impregnated bednet would enter neighbouring dwellings where people used untreated nets. In each of the six experimental huts a man slept under a bednet for six weeks during the dry season in The Gambia. One bednet was impregnated with permethrin, the other five nets were untreated. The design of the trial was based on a series of Latin squares, so that both men and nets were rotated between huts on different nights. At the end of the trial each man had slept under each net in each hut. Mosquitoes collected from the huts each morning were used to estimate the total number of mosquitoes which had entered each hut during the night. Fewer Anopheles gambiae Giles (sensu lato), A. pharoensis Theobald and Mansonia spp. entered a hut with an impregnated bednet than those with untreated nets. However, there was no evidence that mosquitoes deterred from entering a hut with a treated net entered neighbouring huts with untreated nets. Thus it appears unlikely that people using untreated bednets in a community where most use impregnated nets would receive more bites than if everyone. had an untreated net. However, the responses of mosquitoes to permethrin-impregnated bednets were found to depend both upon their species and nutritional condition since A. rufipes Gough, banded Culex spp. and non-human bloodfed A. gambiae (sensu lato) freely entered huts with a treated net.