Susceptibility of Nebraska Western Corn Rootworm (Coleoptera: Chrysomelidae) Populations to Bt Corn Events.

Transgenic plants have been widely adopted by growers to manage the western corn rootworm, Diabrotica virgifera virgifera LeConte, in field corn. Because of reduced efficacy in some Nebraska fields after repeated use of Cry3Bb1-expressing hybrids, single plant bioassays were conducted in 2012 and 2013 to characterize the susceptibility of western corn rootworm populations to the rootworm-active proteins Cry3Bb1, mCry3A, and Cry34/35Ab1. Results demonstrate that there are heritable differences in susceptibility of Nebraska western corn rootworm populations to rootworm-active Bt traits. Proportional survival and corrected survival data coupled with field histories collectively support the conclusion that a level of field resistance to Cry3Bb1 has evolved in some Nebraska populations in response to selection pressure and that cross-resistance exists between Cry3Bb1 and mCry3A. There was no apparent cross-resistance between Cry34/35Ab1 and either Cry3Bb1 or mCry3A. The potential implications of these results on current and future corn rootworm management strategies are discussed.