| Based on five transgenic Bt corns G03-2396,G03-2739,G04-591,G04-676,W04-134 and one non-transgenic Bt corn SUYU16 as the control, we selected out two varieties with the highest resistance to Asian corn borer by studying, and than with these two transgenic varieties as materials we studied the resistant effects and mechanisms of transgenic Bt corn on Asian corn borer. The results were as following:By identifying the resistance of five transgenic Bt corns above, we found that the resistances of G03-2396,G03-2739 were highest, the resistance of W04-134 was lower than G03-2396,G03-2739, the resistances of G04-591,G04-676 were the lowest. Results in the laboratory showed that whorl leaves of G03-2396,G03-2739 had obviously influences on the neonate larvae and the third instar larvae of the Asian corn borer, the resistance of ears to Asian corn borer was lower than whorl leaves, its resistance to the third instar larvae was especially lower and had no significant differences compared to the control. After feeding on these two transgenic Bt corns, the pupation rate,the emergence rate,the pupa weight and the eggs laid per female were also be affected and all lower than the control.Based on the varieties of G03-2396,G03-2739, we studied influences of them on the population dynamics and rules of each instar Asian corn borer (1~5). The results showed that after eating whorl leaves of these two varieties, the longevity of the first instar larvae was only 6 days, the second and the third instar larvae nearly total died after feeding on 10 days, the first to the fourth instar larvae either entirely died and can't pupation, either the average pupa weight was significantly lower than the control, only the result of the fifth instar larvae didn't have significant differences with the control. In the laboratory we found that whorl leaves and ears of these two transgenic Bt corns had produced the effect to the adult longevity,the eggs laid per female and the eggs incubated too. Study also showed that the resistance of ears to Asian corn borer was lower than whorl leaves, it is probably that the toxic protein expressed in ears was less than that expressed in whorl leaves and its insecticidal function wasn't stronger than that in whorl leaves.By farther analyzing the influences of the two transgenic Bt corns on the growth,development and nutritional indices of Asian corn borer, we found that the mortality of the third and the fifth instar larvae feeding on whorl leaves was higher than ears, though ears didn't have significant effects to the mortality of the larvae, they had obvious influences to the weight increasing of each instar larvae. After feeding the third instar larvae of Asian corn borer 3 days and 6 days with whorl leaves of two transgenic Bt corns, the food ingestion and the relative growth rate of the larvae had significantly been restrained, but the effect to the conversion efficiency of digested food and ingested food and the relative metabolize rate were not obvious; when the third instar larvae eating ears of these two transgenic Bt corns 6 days, the conversion efficiency of digested food and ingested food were significantly lower than the control; when the fifth instar larvae feeding on ears of two transgenic Bt corns 3 days, the influence to each nutritional indices was more obvious than feeding on whorl leaves.Using the enzyme-linked immunosorbent assay (ELISA) method, we detected the toxic protein expressed in tissues of two transgenic Bt corns G03-2396,G03-2739,the content of the toxic protein in different instar larvae of Asian corn borer feeding on those two transgenic Bt corns and the control and the content of the toxic protein in the feces of different instar larvae feeding on the corn varieties supplied. We found that: (1) Whorl leaves and ears were all expressed Bt insecticide protein, and the content of the toxic protein expressed in whorl leaves was significantly higher than the content in ears. (2) The content of the toxic protein expressed in the third instar larvae of Asian corn borer feeding on whorl leaves and ears were higher than the fifth instar larvae, and the toxic protein expressed in the third instar larvae feeding on whorl leaves was higher than they feeding on ears. (3) The toxic protein content in the feces of the third and the fifth instar larvae eating with whorl leaves were higher than feeding on ears, the toxic protein in feces of the fifth instar larvae feeding on different tissues were higher than that in the third instar larvae but the difference wasn't significant.By detecing activities of two detoxification enzymeα-naphthylacetate esterase and glutathione-S-transferase in different instar larvae of Asian corn borer, we found that after feeding on whorl leaves and ears of two transgenic Bt corns 3 days, the activity ofα-naphthylacetate esterase in the third instar larvae had significantly been restrained, and the restrain ability toα-naphthylacetate esterase of feeding on whorl leaves was stronger than feeding on ears; compared with the third instar larvae, the influence on theα-naphthylacetate esterase in the fifth instar larvae by eating whorl leaves and ears of those two transgenic Bt corns wasn't obvious. In additional, when the third instar larvae eating whorl leaves of those two transgenic varieties, the activity of glutathione-S-transferase in the larvae had significantly been affected, the others didn't have obvious differences to the control. |
