Development and characterization of western corn rootworm (Diabrotica virgifera virgifera LeConte) resistant to non-Cry insecticidal proteins Mpp75Aa1.1 and Vpb4Da2

Transgenic maize expressing Bacillus thuringiensis (Bt) proteins, and more recently DvSnf7 dsRNA, has been adopted across the Midwestern U.S. Corn Belt to control western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte) and other corn rootworm species. However, resistance has been reported to all five Bt proteins currently used to control WCR. This leaves DvSnf7 dsRNA as the only trait active against WCR without reported field resistance, emphasizing the need for alternative management tools. Mpp75Aa1.1 from Brevibacillus laterosporus and Vpb4Da2 from Bt are two proteins with high efficacy against WCR that do not have cross-resistance to any current commercial Bt protein. To predict the nature of future WCR field resistance to these proteins when used in planta, WCR colonies resistant to maize plants expressing either Mpp75Aa1.1 or Vpb4Da2 were developed by repeated selection on plants containing that protein. We confirmed resistance for both the Mpp75Aa1.1-selected colony (after generation 13, with 10 under selection) and the Vpb4Da2-selected colony (after generation 14, with 10 under selection) using larval recovery and beetle emergence assays with insecticidal protein-expressing maize seedlings and protein diet bioassays. Mpp75Aa1.1-resistant WCR survived and emerged comparably on Mpp75Aa1.1-expressing and non-traited maize, and exhibited a concentration response with an estimated resistance ratio of 5 on diet containing Mpp75Aa1.1. Vpb4Da2-resistant WCR also survived and emerged comparably on Vpb4Da2-expressing and non-traited maize and had no concentration response (i.e., no mortality) on diet containing Vpb4Da2, indicating a high level of resistance. Dominance for both resistant WCR colonies ranged from semidominant to incompletely recessive with increasing dose; effective dominance was estimated to be 0.23 (95% CI 0.12-0.35) and 0.24 (0.16-0.32) for Mpp75Aa1.1 and Vpb4Da2, respectively. These resistant colonies will be a useful tool for understanding the risk of WCR evolving resistance to these proteins when they are deployed commercially in maize.