Pyrethroid-impregnated bednets and curtains are widely employed to reduce the risk of
malaria transmission, but
pyrethroid-resistance is becoming more prevalent among
malaria vector Anopheles mosquitoes (Diptera: Culicidae). As an alternative treatment for curtains, we assessed
carbosulfan (a
carbamate insecticide) in comparison with
permethrin as the standard
pyrethroid, against endophilic female mosquitoes of the Anopheles gambiae Giles complex in a village near Ouagadougou, Burkina Faso. The main criterion evaluated was the impact of curtains (hung inside windows, eaves and doorways) on the number of An. gambiae s.l. females active indoors at night. Light-traps were operated overnight (21.00-06.00 hours beside occupied untreated bednets) to sample mosquitoes in houses fitted with net curtains treated with
carbosulfan 0.2 g ai/m2 or
permethrin 1 g ai/m2 or untreated, compared with houses without curtains. The treated and untreated curtains significantly reduced the numbers of mosquitoes collected indoors, compared with houses without curtains.
Carbosulfan-treated curtains had a highly significantly greater effect than
permethrin-treated or untreated curtains, the scale of the difference being estimated as three-fold. However, there was no significant difference between the impact of untreated and
permethrin-treated curtains on densities of An. gambiae s.l. trapped indoors. Samples of the An. gambiae complex comprised An. arabiensis Patton and both the S- and M-forms of An. gambiae Giles s.s. Susceptibility tests revealed some resistance to
DDT and low frequencies of
permethrin-resistance, insufficient to explain the poor performance of
permethrin on curtains. Among survivors from the diagnostic dosage of
permethrin were some specimens of all three members of the An. gambiae complex, but the kdr resistance mechanism was detected only in the S-form of An. gambiae s.s. Questions arising for further investigation include clarification of resistance mechanisms in, and foraging behaviour of, each member of the An. gambiae complex in this situation and the need to decide whether
carbosulfan-treated curtains are acceptably safe for use to reduce risks of
malaria transmission.