Abstract: Activities of detoxifying enzymes in resistant- and susceptible-imidacloprid endusymbiotic strains of rice brown planthopper, Nilaparvata lugens were compared. The results showed that resistant- and susceptible-imidacloprid strains had significant difference in activities of detoxifying enzymes, in which, activities of carboxylesterase, mixed function oxidase in resistant-imidacloprid strains were significantly higher than those in susceptible-imidacloprid strains, while activity of glutathione-S-transferase showed no obvious difference between resistant-and susceptible-imidacloprid strains. It was suggested that resistant increasing of N. lugens symbiotes to imidacloprid was related to enhencement of carboxylesterase, mixed function oxidase activities．

Key words: Nilaparvata lugens endosymbiotes, resistant-imidacloprid strain, susceptible-imidacloprid strain, activity of detoxifying enzymes, resistance