The toxicity of γ‐BHC and Diazinon when applied over a period of time to adults of the desert locust,Schistocerca gregaria(Forsk.), has been determined. The insecticides were applied in oil solutions, by means of the micro‐drop syringe, to the ventral surface of the abdomen.When doses were applied in two equal portions with a 72 hr. interval, or in four equal portions at 24 hr. intervals, no significant decrease in toxicity, in comparison with a single dose, could be detected with either insecticide. It is concluded, therefore, that if similar effects occur when locusts are sprayed with these insecticides in the field, successive spraying will be fully cumulative over a period of 72 hr. Previous work using DNC has shown that doses applied over 4 days were only half as effective as equivalent single doses and that continued dosing after 4 days brought about very little increase in kill.The sexes were similar in resistance to γ‐BHC when the doses were measured in μg./g., but females were considerably more resistant to Diazinon th