A Comparison of Chemoreceptor and Whole-Fly Responses to DDT and Parathion1

Abstract

A lethal dose of topically applied DDT resulted in the labellar hairs (chemoreceptor) showing about 6 times greater sensitivity to a sucrose solution. The increased hair sensitivity was evident within 1½ minutes after DDT treatment, but detectable symptoms (hyperextension of legs) never occurred before 4 minutes. The chemoreceptor failed to respond to sucrose 10 to 11 minutes after treatment, a time which corresponded to the knockdown stage. The labellar hairs showed increased sucrose sensitivity at a DDT dose about 4 times lower than the lowest dose capable of producing symptoms or about 350 times lower than the LD 50. Parathion, in contrast to DDT, did not produce any greater effect on labellar hair sensitivity than on the entire fly. For example, a dose corresponding to the LD 95 (O.062 µg parathion per fly) did not change the sensitivity response of the hairs to sucrose. The chemoreceptor sensitivity remained at a normal level until the symptoms of hyperactivity. Subsequently no response occurred through death.