The Impact Of Bt Transgenic Corn And Cotton On Non-target Organisms

The wide adoption of Bt transgenic crops provide important methods for controlling insect pests, reducing the application of insecticides. However, the efficacy of Bt crops to target pests need to be evaluated and whether Bt crops exert undesirable effects on non-target arthropods (NTAs) is still controversial. In this study, we assessed the efficacy of BT38and BT799producing CrylAc toxins to the primary target pests and their impact on NTAs. In addition, we also studied the potential effects of CrylAc/Cry2Ab cotton and Cry1F corn on life history parameters of natural enemy Amblyseius andersoni Chant (Acari:Phytoseiidae), hoping to provide some evidence for environmental risk assessment of Bt crops. Here are the main results:Ⅰ. The efficacy of BT38and BT799to the primary target pests and their impact on NTAsThe efficacy of BT38and BT799to Mythimna separata Walker, Ostrinia furnacalis Guenee and Helicoverpa armigera Hubner was confirmed by transferring pest larvae to the crops. The results showed that BT38and BT799showed high efficacy to O. furnacalis, while the efficacy to M. separate and H. armigera was not high enough, which need further evaluation. Visual sampling was conducted to assess NTAs density, biodiversity and community structure of BT38(2009-2011) and BT799(2012-2013). On each sampling date, the total abundance, Shannon’s diversity index (H), Pielou’s evenness index (J) and Simpson’s diversity index (D) were not significantly affected by Bt corn as compared to non-Bt corn. The "sampling dates" had a significant effect on these indices, but no clear tendencies related to "Bt corn" or "sampling dates X corn variety" interaction were recorded. Bray-Curtis dissimilarity and distance analysis showed that Cryl Ac toxin exposure did not increase community dissimilarities between Bt and non-Bt corn plots and that the evolution of non-target arthropod community was similar on the two corn varieties. Taken together, results from the present work support that Bt corn producing Cryl Ac toxins does not adversely affect NTAs.Ⅱ. The effects of Bt crops on A. andersoni, a predator of the two-spotted spider mite, Tetranychus urticae KochA tri-trophic study was conducted to evaluate the potential effects of CrylAc/Cry2Ab cotton and Cry1F corn on life history parameters (survival rate, development time, fecundity and egg hatching rate) of A.andersoni. Our results indicate that there were no differences in any of the life history parameters of A.andersoni. Additional studies confirmed that T. urticae contained biologically active Cry proteins. The two-choice experiment revealed that A.andersoni had no preference for Bt cotton-or corn-reared T. urticae compared with those reared on non-Bt cotton or corn. These results show that A.andersoni is not affected by Cry1Ac/Cry2Ab cotton or Cry1F corn.