Western Corn Rootworm (Coleoptera: Chrysomelidae) Larval Movement in eCry3.1Ab+mCry3A Seed Blend Scenarios

Corn fields planted with plant-incorporated Bacillus thuringiensis (Bt) proteins must have a portion of the field planted with non-Bt, isoline, plants that serve as a refuge for susceptible insects. In the Corn Belt, refuge seeds are now blended in the bag with Bt seeds for corn hybrids containing two or more toxins targeted toward the western corn rootworm, Diabrotica virgifera virgifera LeConte. Syngenta's corn hybrid, Agrisure Duracade, containing the eCry3.1Ab (event 5307) and mCry3a (event MIR604) rootworm-targeted toxins were registered as a seed blend in 2014. Western corn rootworm larval movement between the refuge plants and the Duracade plants was assessed to determine western corn rootworm survival and amount of root damage on these plants when planted in all possible seed blend scenarios. In this study, western corn rootworm larvae moved between isoline and Bt plants and adult survival was greater on Bt plants if movement from a neighboring infested isoline plant had occurred. However, root damage to these Bt plants did not reach economic levels. The low numbers of western corn rootworm larvae that did move from an infested Bt plant to an isoline plant could potentially select for resistance if they survived to adulthood.