Comparing block and blended refuge strategies for managing resistance of western corn rootworm to Bt corn

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is a significant pest of corn in the US. Transgenic corn producing rootworm killing endotoxins derived from Bacillus thuringiensis (Bt) has been available to producers since 2003. The goal of insect resistance management is to preserve pest susceptibility. The use of refuges is one tactic in insect resistance management that can delay pest adaptation to Bt crops. Through a laboratory selection experiment, we compared the effectiveness of a blended refuge and a block refuge at delaying rootworm resistance to Bt corn. Adult D. v. virgifera were captured from fields throughout the Corn Belt and crossed with a non-diapausing strain. This new strain was divided into four; two strains reared under different refuge strategies (block versus blended refuge), one strain selected on Bt corn, and one strain reared on isoline corn, which was an unselected control. Data were collected on survival and emergence for the first three generations of selection, and bioassays were preformed to evaluate the rate of adaptation per strain. Understanding how D. v. virgifera adapts under differing refuge strategies can help inform insect resistant management decisions in the future.