Abstract: Enzyme linked immunosorbent assay was used to determine the activity of PNOD in the midgut and fat body of Bombyx mandarina under cypermethrin treatment. The results showed that after 24 h induction by cypermethrin, the PNOD activity of fat body and midgut increased by 18.7% and 12.2%, respectively. According to the sequence of CYP9A20(GenBank No. FJ378716), CYP9A21(GenBank No. FJ265741), CYP9A22(GenBank No. EF535806) and CYP9G3 gene segments of Bombyx mandarina, the specific primers were designed. The expression levels of CYP9 family genes of Bombyx mandarina induced by cypermethrin were determined by semi-quantitive RT-PCR. The results indicated that after 24 h induction, the relative mRNA level of CYP9A21 in midgut was 2.1 times of the control, and the relative mRNA levels of CYP9A20, CYP9A21, CYP9G3 in fat body were 1.9, 3.5 and 1.4 times of the control, respectively. The over expression of these cypermethrin P450 genes might enhance the oxidation and detoxification capacity of Bombyx mandarina to cypermethrin．

Key words: Bombyx mandarina, cytochrome P450, CYP9 family genes, semi-quantitive RT-PCR