The effects on resistant mosquitoes of interrupted exposure to insecticides

Abstract In paired tests on batches of malathion‐ and dieldrin‐resistant Anopheles arabiensis, one of each pair received a continuous exposure to either malathion or dieldrin for 16 h or more, while the other received a non‐exposed rest phase in the middle of the exposure period. Among dieldrin‐resistant mosquitoes, the mortality rate was decreased in the group that experienced the interrupted, as opposed to the continuous exposures; however, the survival rate of malathion‐resistant adults was unaffected by interrupted exposure. There was a significant positive correlation between the mortality rate and the adult age for malathion, but the responses to dieldrin were independent of age. Movement of adult mosquitoes to and from malathion deposits in sprayed houses should not impair the efficacy of this insecticide, whereas prolonged absence from contact with dieldrin would require even longer exposures to achieve the same mortality in the insects.