(1st Place) Inheritance and fitness costs of field-evolved resistance to Gpp34/Tpp35Ab1 maize by western corn rootworm (Coleoptera: Chrysomelidae)

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is a serious pest of maize in the United States and an invasive pest in Europe. Since 2003, this pest has been managed in the United States with maize hybrids that produce insecticidal proteins derived from the bacterium Bacillus thuringiensis (Bt). Bt maize reduces root-feeding injury by WCR larvae. The widespread use of the Bt protein Gpp34/Tpp35Ab1, and other factors, may have contributed to the field-evolved resistance. Insect resistance management (IRM) plans include the refuge strategy to delay the evolution of resistance to Bt crops, with refuges of non-Bt host plants serving as a source of Bt-susceptible individuals. Mating between resistant individuals and susceptible individuals from refuges produces progeny that are heterozygous for resistance. As such, the dominance of resistance will influence the rate of resistance evolution, with more dominant resistance contributing to a higher rate of resistance evolution. The effectiveness of a refuge in sustaining Bt-susceptible individuals can be compromised when resistance alleles accumulate in the refuge. However, fitness costs act to reduce resistance allele frequency within refuges and preserve the dynamic of refuges producing Bt-susceptible genotypes. Our objectives were to measure the inheritance and fitness costs of resistance to Gpp34/Tpp35Ab1 maize for WCR strains with field-evolved resistance. This research will aid in assessing the risk of continued resistance evolution and in developing more effective IRM approaches to manage resistance. More broadly, our work will help to improve resistance management for Bt crops and other transgenic insecticidal traits.