Abstract: Activities of methoxyresorufin O-demethylase, ethoxyresorufin O-deethylase, ethoxycoumrin O-deethylase, aryl hydrocarbon hydroxylase and aldrin epoxidase were studied in three tissues of a fenvalerate-resistant strain and a susceptible strain of Helicoverpa armigera. Compared with the susceptible strain, activities of the five monooxygenases in the resistant strain increased 11.29-, 4.10-, 2.66-, 6.30-, 2.34-folds respectively in midgut microsomes, 1.46-, 6.80-, 1.36-, 4.05-, 1.48-folds respectively in fat body microsomes and 12.32-, 2.2-, 1.33-, 0.80-, 0.51-folds respectively in integument microsomes. The ability to oxidize the five substrates was different for the three tissues in both strains. Generally, midgut or fatbody microsomes showed the highest monooxygenase activity.

Key words: Helicoverpa armigera, resistance, mixedfunction oxidases, monooxygenase