SEASONAL VARIATIONS IN SUSCEPTIBILITY TO INSECTICIDES OF WILD-CAUGHT EAST AFRICAN ANOPHELES GAMBIAE.

Monthly tests of the susceptibility to insecticides of wild-caught Anopheles gambiae were made at two places in Tanganyika to see what seasonal variations might be revealed. Over a period of three years the susceptibilities were found to vary over a range of two to three times at different visits. The impression was at first gained that the susceptibilities to chlorinated hydrocarbon insecticides were in some way connected with the rainfall, but later work made this seem unlikely. Of all the factors considered which might affect the susceptibility only the temperature at the time of exposure could be found to have had an effect and it was concluded that this was largely responsible for the variations.