Abstract: In order to clarify the physiological effect of Cry1Ac toxin on the oriental armyworm, Mythimna separata (Walker), the activities of two detoxification enzymes (esterase and glutathione-S-transferase), three protective enzymes (superoxide dismutase, catalase and peroxidase) and midgut proteases (total protease, trypsin-like enzyme and chymotrypsin-like enzyme) in the 5th instar larvae of M. separata fed on Cry1Ac toxin were evaluated in the laboratory. The results showed that the activities of esterase, glutathione-S-transferase, peroxidase, trypsin-like enzyme and chymotrypsin-like enzyme in the larvae fed on an artificial diet containing Cry1Ac toxin were significantly lower than those of the control (P<0.05). However, the activity of superoxide dismutase in the larvae fed on the artificial diet containing Cry1Ac was significantly higher than that of the control (P<0.05). The activity of catalase of the treated larvae was obviously lower than that of the control at 6 h, 12 h and 24 h after treatment (P<0.05), but higher than that of the control at 36 h after treatment (P<0.05). These results suggest that the Cry1Ac toxin disturbs the regular metabolism of insects mainly through restraining the activities of detoxification enzymes and proteases and disturbing the balance among superoxide dismutase, catalase and peroxidase in the midgut of larvae, and thus kills the pests.

Key words: Mythimna separata, CrylAc toxin, detoxification enzymes, protective enzymes, proteases, enzyme activity