Cumulative Effect of Sub-Lethal Doses of Insecticides on Houseflies

Abstract

THE effectiveness of repeated small doses of insecticides is of considerable practical importance. For example, mosquitoes and houseflies entering houses treated with residual insecticides make intermittent contacts with deposits, and tsetse flies may receive a succession of doses when applications of insecticides are made from aircraft on a number of parallel runs in each day's sortie, and the area treated at the end of one sortie is re-treated at the beginning of the next. Hoffmann, et al. ¹ exposed houseflies intermittently to small amounts of DDT residues and found that the longer the intervals between exposures the greater the number of flies that survived. There is, however, little quantitative information, and the experiments summarized below were designed to determine the cumulative effect of sub-lethal doses of insecticides on houseflies.