Response of Cry3Bb1‐resistant western corn rootworm (Coleoptera: Chrysomelidae) to Bt maize and soil insecticide

Abstract

AbstractCry3Bb1‐resistant western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is abundant and widely distributed in Iowa. Possible options for management of Cry3Bb1‐resistant populations may include planting of Cry34/35Ab1 maize, maize pyramided with Cry3Bb1 and Cry34/35Ab1 and application of soil‐applied insecticide to either Bt maize or maize that lacks a Bt trait targeting corn rootworm. However, empirical evidence is lacking about how these tactics will affect root injury to maize and survival of this pest to adulthood. We conducted a 2‐year field experiment, in fields known to harbour Cry3Bb1‐resistant western corn rootworm, and quantified the effects of five maize hybrids with and without soil‐applied insecticide, measuring emergence of adults and root injury. Maize with Cry34/35Ab1, both alone or pyramid with Cry3Bb1, significantly reduced the number of adults and the level of root injury, indicating that it was a useful tool for the mitigation of Cry3Bb1‐resistant rootworm. An application of soil insecticide reduced the level of adult emergence and root injury in non‐Bt maize and Cry3Bb1 maize. However, it did not provide any additional reduction in adult emergence or root injury when applied to Cry34/35Ab1 maize or pyramid maize. Both adult emergence and root injury were similar between soil insecticide applied to non‐Bt maize and Cry3Bb1 maize. Our results indicate that useful strategies to manage Cry3Bb1‐resistant rootworm include Cry34/35Ab1 maize, either alone or in a pyramid, and soil insecticide applied to maize lacking a rootworm active Bt toxin, in addition to other IPM practices such as crop rotation.