Abstract: Enhanced detoxification mediated by microsomal cytochrome P450s is a major mechanism responsible for pyrethroid resistance in Helicoverpa armigera. Our previous study showed that constitutive overexpression of CYP9A12 and CYP9A14 was associated with high levels of pyrethroid resistance in the pyrethroid-resistant YGF strain of H. armigera, and functional expression of CYP9A12 and CYP9A14 in yeast provided direct evidence on their involvement in pyrethroid resistance. In this study, molecular cloning, mRNA expression, and functional expression of CYP9A17v2 of H. armigera were investigated in order to verify possible involvement of CYP9A17v2 in pyrethroid resistance. The results showed that protein sequence of CYP9A17v2 has very high identity (94%) to that of CYP9A12. CYP9A17v2 in the fat body of the final-instar larva of the YGF strain had 10.9-fold overexpression compared with that of the control strain (YG), but no overexpression was detected in the midgut. Functional expression in yeast (Saccharomyces cerevisiae) showed that CYP9A17v2 had the capability of metabolizing several pyrethroids (esfenvalerate, deltamethrin, and cyhalothrin). It is so concluded that constitutive overexpression of CYP9A17v2 also contributes to pyrethroid resistance in the YGF strain of H. armigera. Together with previous findings, three P450 genes (CYP9A12, CYP9A14 and CYP9A17v2) from the CYP9A subfamily are confirmed to be involved in oxidative detoxification of pyrethroids in H. armigera.

Key words: Helicoverpa armigera, cytochrome P450, CYP9A17v2, constitutive overexpression, pyrethroids, insecticide resistance