Impact of sustained use of insecticide-treated bednets on malaria vector species distribution and culicine mosquitoes.

Insecticide-treated bednets (ITNs) significantly reduce malaria vector populations. Susceptibility to ITNs differs by vector species, and culicine mosquitoes have not been shown to be significantly affected by the use of ITNs. We examined the impact of 2-4 yr of ITN use on malaria vector species distribution and culicine mosquitoes. Routine entomological surveillance was conducted in adjacent areas with and without ITNs from November 1999 to January 2002. Use of ITNs reduced the proportion of Anopheles gambiae Giles relative to Anopheles arabiensis Giles. The number of culicines per house was significantly lower in the ITN area than in the neighboring area. Changes in the An. gambiae sibling species distribution may help to explain apparent mosquito behavioral changes attributed to ITNs. Reductions in culicines by ITNs may have implications for community perceptions of ITN effectiveness and for control of other diseases such as lymphatic filariasis.