INHIBITION BY INSECTICIDES OF PARTIALLY PURIFIED CARBOXYLESTERASE FROM APHIS-GOSSYPII (HOMOPTERA, APHIDIDAE)

Inhibition of partially purified carboxylesterase from a dichlorvos se lected (ED-R) strain of cotton aphid, Aphis gossypii (Glover), by sele cted insecticides was demonstrated. in vitro. Regeneration of active e nzymes was not observed up to 5 h after removal of excess inhibitor. T his result indicates that pesticide hydrolysis is not a likely resista nce mechanism in A. gossypii. Carboxylesterases from this aphid seem l ikely to bind permanently to inhibitors, rendering them ineffective an d thus protecting the active sites of pesticide inhibition. Of 2 organ ophosphate and 2 carbamate insecticides tested, dichlorvos was most in hibitory. The order of toxicity ranked dichlorvos > naled > carbaryl > m-tolyl methylcarbamate.