Impacts of genetically engineered crops on non-target herbivores: Bt -corn and monarch butterflies as a case study

A wide variety of transgenic insecticidal crops have been field-tested in the United States and three - corn, cotton, and potato - have been commercialized and planted extensively (Gould 1998, Federici 1998). These crops have been modified to produce insecticidal toxins derived from genes of the bacterium Bacillus thuringiensis (Bt). Planting of millions of hectares of these crops has raised questions about selection for resistant pest populations and ecological disruption of food webs (Gould 1998, McGaughey et al. 1998, Obrycki et al. 2001). This chapter focuses on identifying and assessing the risks to non-target herbivorous insect species resulting from transgenic insecticidal corn that was developed to control selected lepidopteran species feeding on aboveground portions of the corn plant (Koziel et al. 1993, Pilcher et al. 1997, Williams et al. 1997, 1998, Anonymous 1999). Many of the principles developed for this risk assessment will be applicable to risk assessment for other crops and toxins.