The western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) is a serious pest of corn in the midwestern United States and is currently managed by planting transgenic corn that produces insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt). In some portions of the Midwest, western corn rootworm has evolved widespread resistance to transgenic corn producing Bt toxin Cry3Bb1. Resistance to Cry3Bb1 has been found to extend to Bt toxins mCry3A and eCry3.1Ab through cross-resistance. More recently, evidence of emerging resistance to Cry34/35Ab1 corn by western corn rootworm also has been found, which means that, for some western corn rootworm populations, all available Bt traits have been compromised by resistance. This presentation will draw on data from bioassays and geospatial analyses to address what is known about the geographic distribution of resistance and the effects of the agricultural landscape on resistance evolution. In general, the risk of resistance to Bt corn by western corn rootworm is elevated because of non-recessive inheritance of resistance and minimal fitness costs of resistance. Analysis of field-history data and geospatial patterns of corn cultivation suggest that key factors affecting resistance in the agricultural landscape include cultivation of corn for multiple consecutive years within a field and using the same Bt traits for multiple consecutive years. Factors that should help to delay additional cases of Bt resistance include reducing the number of years a field is planted to corn and reducing reliance on Bt traits for management of western corn rootworm.
