Western corn rootworm (Coleoptera: Chrysomelidae) larval movement in eCry3.1Ab+mCry3A seed blend scenarios

Authors: ZUKOFF, SARAH - Kansas State University; ZUKOFF, ANTHONY - Kansas State University; Geisert, Ryan; Hibbard, Bruce

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2016
Publication Date: 5/17/2016
Citation: Zukoff, S.N., Zukoff, A.L., Geisert, R.W., Hibbard, B.E. 2016. Western corn rootworm (Coleoptera: Chrysomelidae) larval movement in eCry3.1Ab+mCry3A seed blend scenarios. Journal of Economic Entomology. 109(4):1834–1845.

Interpretive Summary: The use of genetically modified corn with resistance to feeding by corn rootworm larvae offers a viable alternative to insecticides for managing the most economically important insect pest of corn. Maintaining susceptibility to Bt crops is in the interest of growers, the Environmental Protection Agency (EPA), and industry, but requires an understanding of corn rootworm biology that does not currently exist. Bt corn fields must have a portion of the field planted with non-Bt plants which serve as a refuge for insects susceptible to the Bt toxins. Recently, the EPA registered a seed mix of Bt and non-Bt corn as products targeting the western corn rootworm (WCR). Movement between Bt and non-Bt corn can speed the development of resistance, but currently the effects of larval movement on resistance formation are unknown. We assessed movement of WCR larvae among four configurations of Bt and non-Bt plants. We found that larvae moved between non-Bt and Bt plants and adult survival was greater on Bt plants if movement from a neighboring infested non-Bt plant had occurred. Root damage to these Bt plants did not reach economic levels. This information is important to seed companies, the EPA, and system modelers in their attempts to develop resistance management plans for Bt corn. Implications of larval movement and the occurrence of Bt resistance in seed blends are discussed.

Technical Abstract: Corn fields planted with plant-incorporated Bacillus thuringiensis (Bt) proteins must have a portion of the field planted with non-Bt, isoline, plants which 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 was 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 varying 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. Implications of larval movement and the occurrence of Bt resistance in seed blends are discussed.