The Impact of Environmental Stress on Bt Crop Performance

Bt crops have been grown commercially for more than two decades. They have proven remarkably effective in the control of target insect pests. However, Bt crops can become less effective under various forms of environmental stress. Most studies in this area have considered the effect of environmental stress on Bt insecticidal protein levels or target pest mortality, but not both, resulting in a lack of mechanistic analysis. In this review, we critically examine previous research addressing the impact of environmental stress on the effectiveness of Bt crops. We find that the body of research data is not sufficiently robust to allow the reliable prediction of the performance of Bt crops under extreme climatic conditions. Reduced effectiveness of Bt crops to control target pests has been largely attributed to the fluctuation in Bt toxin levels caused by various forms of environmental stress.The current body of data shows that downregulation of Bt genes does not always reduce levels of Bt toxin and that lower levels of Bt toxin do not always reduce the effectiveness of Bt crops against target pests.Current approaches do not consider the environmental impact on Bt toxin accumulation and the environmental impact on pest insect mortality in an integrative manner.To successfully predict the performance of Bt crops in future climatic scenarios, multidisciplinary research that considers how both the plants and the pest insect are affected by the environmental stress, as well as the interactions between the plant and pest, is required.