Field-Evolved Resistance by Western Corn Rootworm to Cry34/35Ab1 and other Bacillus thuringiensis Traits in Transgenic Maize.

BACKGROUND: Transgenic crops producing insecticidal toxins from the bacterium Bacillus thuringiensis (Bt) are widely planted to manage agricultural insect pests. However, widespread adoption of Bt crops has led to the evolution of Bt resistance. The western corn rootworm, Diabrotica virgifera virgifera, is among themost serious pests of maize in the midwestern United States and is currently managed with Bt maize. To date, there is evidence of field-evolved resistance to all Bt toxins used to manage this pest. While western corn rootworm resistance to Cry3Bb1, and the closely related mCry3A and eCry3.1Ab traits, is widely distributed within the Midwest, fewer cases of Cry34/35Ab1 resistance have been observed, and planting of Cry34/35Ab1 maize is one of the methods used to manage Cry3-resistant rootworm. RESULTS: We found that fields with high levels of root injury to Cry34/35Ab1 maize by western corn rootworm were associated with Cry34/35Ab1-resistant western corn rootworm. Additionally, a population not associated with high levels of root injury was found to be resistant to Cry34/35Ab1. In all cases, populations that were resistant to Cry34/35Ab1 also were resistant to Cry3 traits. CONCLUSIONS: Western corn rootworm resistance to Cry34/35Ab1 has continued to persist in the agricultural landscape and has likely increased. The presence of rootworm populations with resistance to all available Bt traits threatens the utility of current and future transgenic technologies to manage this pest. Decreased reliance on Cry34/35Ab1 and better use of integrated pest management will be essential to preserve Bt susceptibility in western corn rootworm. (c) 2019 Society of Chemical Industry