Differential Behavioral Responses of Anopheles gambiae (Diptera: Culicidae) Modulate Mortality Caused by Pyrethroid-Treated Bednets

Direct observations of individual Anopheles gambiae s.s. (Diptera: Culicidae) females fleetingly but repeatedly alighting on pyrethroid-treated fabric of long-lasting insecticide treated nets (LLINs) fitted over a human hand proved that onset of behavioral effects modulated mortality. For Olyset Net, containing 1,000 mg of permethrin per m(2), mosquitoes reduced landing attempts and elevated frequency of flight within 3 min. This kinetic disengagement resulted in little mortality. In contrast, mosquito landing attempts on PermaNet (containing 55 mg of deltamethrin per m(2)) were sustained for up to 6 min before disengagement, and mortality was a frequent outcome. The likely disengagement mechanism was loss of response to host cues, which was restored within 24 h. We conclude that optimal LLIN formulations should maximize engagement so as to maximize mortality.