Effects Of Cry1Ac Toxin On Weight And Enzyme Activity Of The Oriental Armyworm, Mythimna Separata

The oriental armyworm, Mythimna separata (Walker)(Lepidoptera:Noctuidae) is a major crops pest in China and other Asian countries, which has brought huge economic losses to grain production in China, but it is not currently Bt crops target pest. It was shown that the population of nontarget pest increased due to the reduction in use of pesticide in genetically modified crops. Therefore, it will be necessary to carry out the evaluation of the effect of genetically modified crops on nontarget pests. In view of the lack of ecological safety evaluation of genetically modified crops on the oriental armyworm, the effect of Cry1Ac toxin on the weight and the activities of two detoxification enzymes (esterase and glutathione-S-transferase), three protective enzymes (superoxide dismutase, catalase and peroxidase) and proteases (total protease, trypsin-like enzyme and chymotrypsin-like enzyme) were researched in the laboratory by physiological methods, so as to analyze the physiological effect of Bt toxin on the oriental armyworm, evaluate the insecticidal effect of genetically modified crops on the oriental armyworm as well as provide new ideas to supplement and improvement of the ecological safety risk assessment of genetically modified crops, acceleration of the commercial production process and the potential resistance management measures. The main results obtained were as follows:Effects of Cryl Ac toxin on weight and midgut protease activity of larvae of the oriental armyworm were researched. It was shown that after feeding on different concentrations (0,0.5,1,2and4μg/g) of Cry1Ac toxin for10,13and16days, with the concentration of Cryl Ac insecticidal protein increasing, the weight of larvae showed a decreasing trend. After feeding the newly hatched larvae with artificial diet containing Cry1Ac toxin for13days, the activity of total protease was significantly higher than that of control under the concentration of0.5μg/g, there were no significant differences between total protease activity under the concentration of1,2,4μg/g and that of the control; the activities of active alkaline trypsin-like enzyme and chymotrypsin-like enzyme were significantly lower than those of control after feeding on different concentrations of Cry1Ac toxin; the activity of weak alkaline trypsin-like enzyme was significantly lower than that of control only under feeding on concentrations of2μg/g and4μg/g Cryl Ac toxin. After feeding on different concentrations (2,4,8and16μg/g) of Cry1Ac toxin for24hours, the average weights and the activities of active alkaline trypsin-like enzyme, weak alkaline trypsin-like enzyme and chymotrypsin-like enzyme of 5th instar and6th instar larvae were significantly lower than those of control; the activity of total protease was significantly lower than that of control when the concentration of Cry1Ac was higher. The results showed that the Cry1Ac toxin significantly inhibited the growth of the oriental army worm and as an exogenous toxin, Cry1Ac toxin worked on the pests midgut after fed with artificial diet or Bt crops, which inhibited the activities of trypsin-like enzyme and chymotrypsin-like enzyme significantly, affected the digestion in the midgut of the oriental army worm and caused the decrease of weight.Effects of CrylAc toxin on activities of detoxification enzymes, protective enzymes and proteases in the5th instar larvae of the oriental army-worm were systematically researched. It was showed that the activities of esterase and glutathione-S-transferase in the larvae fed on artificial diet containing Cry1Ac toxin were significantly lower than those of the control, and with the feeding time increasing the activities gradually reduced. The activity of superoxide dismutase in the larvae fed on artificial diet containing Cry1Ac was significantly higher than that of control; the activity of catalase of the treated larvae was obviously lower than that of the control at6h,12h and24h after treatment, but higher than that of the control at36h after treatment; the activity of peroxidase of the treated larvae was significantly lower than that of the control. The activities of trypsin-like enzyme and chymotrypsin-like enzyme of the treated larvae were significantly lower than those of control; the activity of total protease of the treated larvae was obviously higher than that of the control at12h and24h after treatment, but lower than that of control at36h after treatment. So it was shown that the Cry1Ac toxin may disturb the insect regular metabolism mainly by restraining the activities of detoxification enzymes and proteases and disturbing the balance among superoxide dismutase, catalase and peroxidase in the midgut of larvae, then killed the pests.