Corn rootworms, Diabrotica spp. (Coleoptera: Chrysomelidae), are the most economically important pest of maize in the United States. The larvae consume maize roots, contributing to poor nutrient uptake, lodging of the plants, and severe yield loss. Transgenic maize expressing toxins from the bacterium Bacillus thuringiensis (Bt) have been employed to combat the pest. However, corn rootworm resistance to Bt maize has recently been reported and spurred research on the effectiveness of Bt toxins against corn rootworm across the Corn Belt. Thus, our objectives were twofold. First, we quantified the efficacy of Bt maize hybrids against corn rootworm in South Dakota. Second, we surveyed populations of Diabrotica species in areas where Bt maize had been grown since its commercialization in 2003. Maize hybrids expressing Cry3Bb1, Cry34/35Ab1, and mCry3A were evaluated at two locations with previous corn rootworm infestations or in fields that were in continuous maize for three or more consecutive years. We reported damage to maize expressing Cry3Bb1 and mCry3A toxins. We also observed significantly higher numbers of western corn rootworm than northern corn rootworm in our Diabrotica species surveys, suggesting that western corn rootworm are the dominant species in the region. This research has implications for maize production and sustainable corn rootworm management in South Dakota and the Northern Plains, and will advance our knowledge of the incidence of resistance to Bt toxins and long-term impact of Bt hybrids on species diversity of Diabrotica.
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