Evidence of western corn rootworm (Diabrotica virgifera virgifera LeConte) field‐evolved resistance to Cry3Bb1 + Cry34/35Ab1 maize in Nebraska


BACKGROUND: Western corn rootworm (WCR; Diabrotica virgifera virgifera) field evolved resistance to transgenic maize expressing the Cry3Bb1 protein derived from Bacillus thuringiensis (Bt) has been confirmed across the United States Corn Belt. Although use of pyramided hybrids expressing Cry3Bb1 + Cry34/35Ab1 has increased in recent years to mitigate existing WCR Bt resistance, susceptibility of Nebraska WCR populations to this rootworm-Bt pyramid has not been assessed. Plant-based bioassays were used to characterize the susceptibility of WCR populations to Cry3Bb1 and Cry3Bb1 + Cry34/35Ab1 maize. Populations were collected from areas of northeast Nebraska with a history of planting Bt maize that expressed Cry3Bb1 and Cry34/35Ab1. RESULTS: Significant differences in mean corrected survival among populations within Bt hybrids indicated a mosaic of WCR susceptibility to Cry3Bb1 + Cry34/35Ab1 and Cry3Bb1 maize occurred in the landscape. All field populations exhibited some level of resistance to one or both Bt hybrids when compared to susceptible lab control populations in bioassays. Most WCR populations exhibited incomplete resistance to Cry3Bb1 + Cry34/35Ab1 maize (92%) and complete resistance to Cry3Bb1 maize (79%). CONCLUSION: The present study confirms the first cases of field-evolved resistance to Cry3Bb1 + Cry34/35Ab1 maize in Nebraska and documents a landscape-wide WCR Cry3Bb1 resistance pattern in areas characterized by long-term continuous maize production and associated planting of Cry3Bb1 hybrids. Use of a multi-tactic integrated pest management approach is needed in areas of continuous maize production to slow or mitigate resistance evolution to Bt maize.

Journal of Economic Entomology