Abstract: To clarify the physiological and biochemical mechanism of the effect of transgenic cry1Ab/cry1Ac rice on larvae of Sesamia inferens (Walker), the effects of feeding transgenic Bt rice on the activities of three protective enzymes (SOD, CAT and POD) in S. inferens larvae were studied by assaying enzyme activities in the 3rd and 5th instar larvae which were fed with stems of transgenic and non-transgenic rice (control) for different time. The results showed that SOD activity in the 3rd instar larvae fed with Bt rice for 24 h was significantly higher than that of the control (increased by 43.44%), but declined to the minimum at 48 h after feeding. The POD activity in the 3rd larvae fed with Bt rice reached the maximum at 24 h after feeding, and significantly higher than that of the control （increased by 29.22%）, but declined to the minimum at 48 h after feeding which was significantly lower than that of the control. The CAT activity in the 3rd larvae fed with Bt rice for 4 h increased by 30.33%, and decreased by 27.01% at 48 h after feeding compared with that of the control. The SOD activity in the 5th instar larvae was significantly higher than that of the control after the larvae was fed on transgenic rice for 4 h, but declined to the minimum at 36 h after feeding (decreased by 31.62% compared with that of the control). The POD activity reached the maximum and increased by 73.20% compared with that of the control after the larvae was fed on Bt rice for 8 h, but declined to the minimum at 36 h after feeding. The CAT activity reached the maximum and increased by 75.73% after the larvae was fed with transgenic rice for 4 h and decreased by 7.55% at 48 h after feeding compared with that of the control. The resistance level of the 3rd instar larvae was lower than the 5th instar larvae when treated by transgenic Bt rice for the reason that the 3rd instar larvae had lower defense capability. The results suggest that in the initial stage of feeding, the enzyme activity in larvae increases in order to protect larvae from being damaged by Bt toxalbumin. The enzyme activities in larvae rapidly descend and the metabolism of larvae is disturbed due to feeding transgenic rice with extension of feeding time, causing the poisoning symptoms and even death of larvae.

Key words: Sesamia inferens, transgenic rice, protective enzymes, SOD, CAT, POD