Inhibition by insecticides of partially purified carboxylesterase from Aphis gossypii (Homoptera: Aphididae)

Inhibition of partially purified carboxylesterase from a dichlorvos selected (E-D-R) strain of cotton apbid, Aphis gossypii (Clover), by selected insecticides was demonstrated in vitro. Regeneration of active enzymes was not observed up to 5 h after removal of excess inhibitor. This result indicates that pesticides hydrolysis is not a likely resistance mechanism in A. gossypii. Carboxylesterases from this aphid seem likely to bind permanently to inhibitors, rendering them ineffective and thus protecting the active sites of pesticide inhibition. Of 2 organophosphate and 2 carbamate insecticides tested, dichlorvos was most inhibitory. The order of toxicity ranked dichlorvos > naled > carbaryl > m-tolyl carbamate.