AbstractAvoidance of four strains of Drosophila melanogaster to the pyrethroid insecticide permethrin was studied. All strains showed concentration-dependent avoidance, with avoidance detected at levels as low as 1 ppm. Avoidance was not dependent on the insect acquiring a lethal dose. Some correlation appeared to exist between higher locomotor activity and lower sensitivity to permethrin. The most sensitive strain had the lowest activity. Two of the four strains studied were chosen as permethrin-sensitive mutants following mutagenesis. These two strains had activity levels significantly lower than the original strain from which they were obtained, raising the question as to whether the increased sensitivity to permethrin following mutagenesis reflects an alteration in the target site of permethrin, a neuroactive insecticide.