Studies On The Effects Of Transgenic Cry1Ab+Cry1Ac Rice Against Key Insect Pests In Paddyfields

The striped stem borer, Chilo supperssalis Walker, the pink stem borer, Sesamia inferens Walker and the rice leaffolder, Cnaphalocrocis medinalis Guenee are the important rice pests widely distributed in all rice growing regions in China. In recent years, Lepidoptera pests populations have increased gradually, because of changes in rice cultivation, use of new hybrid varieties and global climate and the occurrence of pest resistance to chemical insecticides. The development of transgenic rice lines expressing Bacillus thuringiensis (Bt) insecticidal protein provide the new strategy for the control of Lepidoptera pests. However, the ecological safety is the main factor for transgenic insect-resistant rice not being approved to be commercial application. In this study, field experiments were carried out to study the occurring characteristics and population dynamics of the main rice pests including the target pests of Chilo suppressalis and Cnaphalocrocis medinalis, the sub-target pests of Sesamia inferens, the nontarget pests of planthoppers and the arthropods feeding on transgenic Bt rice with dual CrylAb and Cry1Ac (cv. HH1) and the parent line nontransgenic rice (cv. MH63).Resistance efficiency of transgenic Bt rice on C. supperssalis, S. inferens and C. medinalis; the succession risk between C. suppressalis and S. inferens under the commercialization usage of transgenic Bt rice; the effect on the nontarget pests of planthoppers and the arthropods were probably conducted. Therefore, the research perhaps provide ecological security evaluation of transgenic Bt rice important scientific data simulating the sustainable application and healthy development of transgenic Bt rice.The main results were as follows:1. Two consecutive seasons-long field experiments were conducted to study the resistance efficiency of transgenic Bt rice on C. medinalis. The results indicated that transgenic Bt rice showed higher resistance to C. medinalis. The natural population life tables of C. medinalis. were established, the results indicated no significant differences in the survival rates of eggs and pupaes while significant decreases were observed in the survival rate of larvas. In addition, transgenic Bt rice showed significant influence on pupa weight. Under a certain eggs density condition in unit area, there were a certain percentage of leaffolder to complete the whole generation, and cause certain damage in transgenic Bt rice. Spawning selectivity tests showed that C. medinalis have no significant preference between transgenic Bt rice and nontransgenic rice.2. In this study, the field experiments were carried out to study the population dynamics and damage characteristics of two stem borers, i.e., the target pest of C. suppressalis and the sub-target pest of S. inferens, feeding on transgenic Bt rice with dual CrylAb and CrylAc (cv. HH1) and its parent line of nontransgenic rice (cv. MH63). The results indicated that stem borer C. suppressalis was still being the key insect pest in the paddyfield. Compared with nontransgenic rice, transgenic Bt rice significantly reduced the population dynamics of C. suppressalis larvae, while no significant difference in the number of larvae per100plants was found for S. inferens. In addition, C. suppressalis had significantly higher larvae abundances than S. inferens when they fed on nontransgenic rice, while no significant differences were found when they fed on transgenic Bt rice. Simultaneously, significantly lower percentages of dead heart or white head plants, and damaged plants were resulted by C. suppressalis, while no significant differences in the damage percentages for S. inferens, as they fed on transgenic Bt rice relative to nontransgenic rice. So transgenic Bt rice has higher resistance to the target pest of C. suppressalis, while lower resistance against the sub-target pest of S. inferens. Furthermore, significantly higher percentages of the above damage indexes were caused by C. suppressalis relative to S. inferens, as they fed on transgenic Bt rice and nontransgenic rice. While it is presumed, owing to the significant inhibition of transgenic Bt rice on the occurrence of the target pest of C. suppressalis relative to the sub-target pest of S. inferens under the commercialization usage of transgenic Bt rice, the inter-species competition and population succession may be happening between the target and sub-target pests of stem borers. The natural population life tables of C. suppressalis were established, the results indicated young larvae (neonates-2rd instar) of C. suppressalis was the critical stage of fluctuation, and the resistance against C. suppressalis gradually reduced with the growth of larvae.3. Two consecutive seasons-long field experiments were conducted to study the population dynamics of two planthoppers, i.e., Nilaparvata lugens Stal and Sogatella furcifera Horvath, feeding on transgenic Bt rice with dual CrylAb and Cry1Ac (cv. HHl) and its parent line of nontransgenic rice (cv. MH63). there were no significant differences in the population abundance of nymphs or adults for N. lugens and S. furcifera fed on transgenic Bt rice. In addition, transgenic Bt rice showed no significant influence on the landed behavior of N. lugens and S. furcifera. The field experiments were conducted to study the population dynamics of mainly arthropods sub-community, there were no significant differences in the population abundance of predatory sub-community, parasitic sub-community, pests sub-community and arthropods community in transgenic Bt rice paddyfield.