Characterizing the relationship between western corn rootworm (Coleoptera: Chrysomelidae) larval survival on Cry3Bb1-expressing corn and larval developmental factors

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is a significant pest of field corn, Zea mays L., across the United States Corn Belt. Rootworm management programs have historically included three main management tactics: crop rotation, soil- or foliar-applied insecticides, and transgenic corn expressing Bacillus thuringiensis(Bt) Berliner proteins. In multiple Nebraska counties, greater than expected injury to Cry3Bb1-expressing hybrids has been observed after widespread adoption and continuous use of the Bt technology.
Single-plant larval bioassays were conducted on larval western corn rootworm populations to determine the level of resistance present in various Nebraska counties. The results confirmed a mosaic of susceptibility to Cry3Bb1 across Nebraska. Larval developmental factors such as mean head capsule width and mean fresh weight were measured to quantify the relationship between the level of resistance to Cry3Bb1 and larval developmental rate. The results suggest that as the level of resistance to Cry3Bb1 within field populations increases, the mean head capsule width and larval fresh weight also increase. Regression and correlation analyses indicate a significant, positive linear relationship between Cry3Bb1 corrected survival and larval development factors. The results provide empirical data from field-collected populations that confirm developmental delays associated with sublethal exposure to Cry3Bb1 decrease as the level of resistance to Cry3Bb1 increases. This information increases our understanding of the impact of sublethal effects of Cry3Bb1 on western corn rootworm larval developmental factors and can inform efforts to mitigate Cry3Bb1 resistance evolution.