Insecticide sensitivity in malaria vectors in high altitude Madagascar after five years of vector control

: In 1991, Anopheles gambiae and Anopheles funestus, the main malaria vectors in the Highlands of Madagascar, were reported to be fully susceptible to DDT; nevertheless a slight decrease in the susceptibility levels was recorded when compared with previous assays carried out in 1962. From 1993 to 1997, five cycles of indoor residual spraying have been carried out in the Highlands: a total of 1,482,000 kg of 70% wp DDT have been used for the treatment of houses and animal shelters. From 1996 to 1999, adult mosquito susceptibility tests to DDT and to some pyrethroids (lambdacyalothrine, deltamethrine, permethrine and cyfluthrine) have been carried out on samples collected in 20 areas of the Highlands. Bioassays were carried out following the WHO standard method. All tested populations of An. funestus showed a full susceptibility to DDT. An. gambiae showed a widespread decrease in the susceptibility to DDT, particularly marked in the region of the capital city Antananarivo. Both species were susceptible to pyrethroids.