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Title: Mortality of western corn rootworm larvae on MIR604 transgenic maize roots: field survivorship has no impact on survivorship of F1 progeny on MIR604

Author
item Hibbard, Bruce
item CLARK, THOMAS - Monsanto Corporation
item ELLERSIECK, MARK - University Of Missouri
item MEIHLS, LISA - University Of Missouri
item EL KHISHEN, AHMED - Monsanto Corporation
item KASTER, VON - Syngenta Seeds, Inc
item YORK-STEINER, HENRY - Syngenta Biotech, Inc
item KURTZ, RYAN - Syngenta Biotech, Inc

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2010
Publication Date: 12/15/2010
Citation: Hibbard, B.E., Clark, T.L., Ellersieck, M.R., Meihls, L.N., El Khishen, A.A., Kaster, V., York-Steiner, H., Kurtz, R. 2010. Mortality of western corn rootworm larvae on MIR604 transgenic maize roots: field survivorship has no impact on survivorship of F1 progeny on MIR604. Journal of Economic Entomology. 103(6):2187-2196.

Interpretive Summary: The registration of transgenic corn with resistance to corn rootworm larval feeding offers a viable alternative to insecticides for managing the most economically important insect pests of corn. Maintaining susceptibility to transgenic crops (resistance management) is in the interest of growers, the Environmental Protection Agency, and industry, but requires an understanding of corn rootworm biology that does not currently exist. Mortality of western corn rootworm larvae due to MIR604 transgenic corn expressing the modified Cry3A (mCry3A) protein relative to survivorship on corn with the same genetic background without the gene (isoline corn) was evaluated at three Missouri sites in both 2005 and 2006. The average mortality due to the mCry3A protein was 94.88% when averaged across all environments and both years. Fifty percent emergence of beetles was delayed about 5.5 days. Beetles were kept alive and their progeny evaluated on MIR604 and isoline corn in the greenhouse to determine if survivorship on MIR604 in the field for one generation increased survivorship on MIR604 in the greenhouse in the subsequent generation. There was no significant difference in survivorship on MIR604 in greenhouse assays between larvae whose parents survived isoline and larvae whose parents survived MIR604 in the field the previous generation, indicating that many susceptible beetles survived MIR604 in the field the previous seasons along with any potentially resistant beetles. Dose calculations of Bt corn targed toward corn rootworms calculated here are important to seed companies and modelers in their attempts to optimize resistance management plans for transgenic corn and are required by the Environmental Protection Agency.

Technical Abstract: Mortality of western corn rootworm (Diabrotica virgifera virgifera LeConte) larvae due to MIR604 transgenic corn (Zea mays L.) expressing the modified Cry3A (mCry3A) protein relative to survivorship on corn with the same genetic background without the gene (isoline corn) was evaluated at three Missouri sites in both 2005 and 2006. We made these comparisons using wild type western corn rootworm at three different egg densities (6,000, 3,000 and 1,500 eggs/m) so that the role of density-dependent mortality would be known. The average mortality due to the mCry3A protein was 94.88% when averaged across all environments and both years. Fifty percent emergence of beetles was delayed about 5.5 days. Beetles were kept alive and their progeny evaluated on MIR604 and isoline corn in the greenhouse to determine if survivorship on MIR604 in the field for one generation increased survivorship on MIR604 in the greenhouse in the subsequent generation. There was no significant difference in survivorship on MIR604 in greenhouse assays between larvae whose parents survived isoline and larvae whose parents survived MIR604 in the field the previous generation, indicating that many susceptible beetles survived MIR604 in the field the previous seasons along with any potentially resistant beetles. The data are discussed in terms of rootworm insect resistance management (IRM).