Abstract: The activities of two metabolic enzymes in the imidaclopridresistant (about 7fold) and susceptible strains of the cotton aphid, Aphis gossypii were compared by biochemical methods. Piperonyl butoxide (Pb) had no synergism to imidacloprid in both of the strains. Activities of carboxylesterases (CarE) and gluathione Stransferases (GSTs) in the resistant strain were significantly higher than that in the susceptible one. The K_m of CarE in the resistant strain were also significantly higher than in the susceptible strain, which means that the resistant strain had higher affinity of CarE with the substrate. The results showed that the enhancement of activities of CarE and GSTs would be the main metabolic mechanism in the resistance of A. gossypii to imidacloprid.

Key words: Aphis gossypii, imidacloprid, resistance mechanism, metabolic enzyme s