Abstract: The effects of transgenic rice on the activities of SOD, CAT and POD in Cnaphalocrocis medinalis larvae were studied by assaying enzyme activities after the 3rd instar larvae had been fed with leaves of transgenic and nontarnsgenic rice (control) for different time. The results showed its SOD activity was significantly higher (91.5%) than that of control after the larvae fed on transgenic rice for 4 h and reached the maximum with a little difference from that of control after the larvae fed for 36 h. The CAT activity of larvae fed with leaves of transgenic rice reached the maximum and was a little higher than that of control after feeding for 24 h, but significantly lower than that of control after the larvae fed for 48 h. The POD activity of larvae fed with leaves of transgenic rice reached the maximum with a little difference from that of control after feeding for 12 h, but decreased by 68.05% after feeding for 48 h. Meanwhile we also assayed the variation of the Bt protein in the larval body and dejecta. By voidance of dejecta, the level of Bt protein in the larval body was always lower than that in dejecta after feeding for 12h, and the difference between both reached the highest at 24 h after feeding. It was so inferred that the gradual accumulation of Bt protein in the larval body disturbed the dynamic balance of SOD, CAT and POD, baffled the clearance of free radicals and produced toxic effects on C. medinalis larvae.

Key words: Transgenic rice, Cnaphalocrocis medinalis, protective enzymes, SOD, CAT, POD, enzyme activity