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Multiple assays indicate varying levels of cross resistance of Cry3Bb1-selected field populations of the western corn rootworm to mCry3A, eCry3.1Ab, and Cry34/35Ab1

Sarah N. Zukoff, Kenneth R. Ostlie, Bruce Potter, Lisa N. Meihls, Anthony L. Zukoff, Lee French, Mark R. Ellersieck, B. Wade French, Bruce E. Hibbard
Journal of economic entomology 2016 v.109 no.3 pp. 1387-1398
Bacillus thuringiensis, Diabrotica virgifera virgifera, United States Environmental Protection Agency, bacterial proteins, corn, cross resistance, diet, larval development, process monitoring, seedlings, weight gain, Minnesota
Minnesota populations of the western corn rootworm (WCR) surviving Cry3Bb1-expressing corn in the field and WCR populations assumed to be susceptible to all Bt proteins were evaluated for susceptibility to Cry3Bb1, mCry3A, eCry3.1Ab, and Cry34/35Ab1 in diet assays and three different plant-based assays. Cry3Bb1-selected WCR populations showed increased survival and/or larval growth on not only Cry3Bb1, but also eCry3.1Ab, mCry3A, and Cry34/35Ab1 in some, but not all, plant and diet assays. Cross resistance was clearly documented between Cry3Bb1 and both mCry3A and eCry3.1Ab. In addition, for one Cry3Bb1-selected population, a resistance ratio of 9.1 was also found to Cry34/35Ab1 when evaluating EC(50) values. This same population showed increased survival and weight gain on Cry34/35Ab1 in seedling assays, although we would not necessarily characterize this increased tolerance for Cry34/35Ab1 as cross-resistance. The United States Environmental Protection Agency recently suggested eliminating diet assays as part of the Bt resistance monitoring process. However, given the variability of responses of WCR populations to different proteins in different assays, both plant and diet assays are needed as options for detecting and fully characterizing resistance.