Bacillus thuringiensis: Transgenic Crops

Bacillus thuringiensis (Bt) crops, genetically modified to express insecticidal toxins that target key pests of corn, cotton, rice, potato, and other crops, have been rapidly adopted and have become dominant fixtures in agroecosystems throughout the world. Due to the constitutive nature of Bt toxin expression, insecticidal proteins may be found in nearly all plant tissues, presenting multiple sources for Bt toxins to enter the environment, thus creating complex direct and indirect pathways for non-target organisms to be exposed to insecticidal proteins. The environmental impacts of Bt crops have been widely debated, although both benefits and risks do exist. Benefits of Bt crop adoption include reduced risks to non-target organisms when compared with conventional spray applications of insecticides, as well as economic savings to growers and increased global food security. Conversely, impacts on non-target organisms, presence in the human food supply, pleiotropic effects of genetic transformation, and gene escape to wild plant populations are all considered as viable risks of Bt technology. To address the potential risks of Bt crop technology, proposed approaches to the environmental management of Bt crops are discussed, including within-plant modifications, reduction in Bt toxin and transgene escape, and large-scale integration into integrated pest and resistance management programs. Additionally, continued study of the effects of Bt toxins on non-target organisms at multiple tiers is necessary for intelligent use of this valuable pest management tool. The global area planted to Bt crops is expanding, and new Bt products and combinations are in various stages of development. Although Bt technology may offer an environmentally superior alternative to many insecticide applications, further risk assessment research addressing the impacts of Bt crops on agroecosystem function are needed to promote environmental safety. 307 digitalcommons.unl.edu 308 Peterson et al. in Encyclopedia of Environmental Management (2013)