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Title: Western corn rootworm larval movement in a SmartStax seed blend scenarios

Author
item ZUKOFF, SARAH - University Of Missouri
item BAILEY, WAYNE - University Of Missouri
item ELLERSIECK, M.R - University Of Missouri
item Hibbard, Bruce

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2012
Publication Date: 8/13/2012
Citation: Zukoff, S.N., Bailey, W., Ellersieck, M., Hibbard, B.E. 2012. Western corn rootworm larval movement in a SmartStax seed blend scenarios. Journal of Economic Entomology. 105(4):1248-1260.

Interpretive Summary: The use of transgenic (genetically modified) corn with resistance to corn rootworm larval feeding offers a viable alternative to insecticides for managing the most economically important insect pest of corn. Maintaining susceptibility to transgenic crops (resistance management) 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. Recently, the EPA registered a seed mix of transgenic Bt (an insecticidal protein derived from bacteria) corn and isoline (non-transgenic control) for one of the products targeting the western corn rootworm (WCR). Movement between transgenic Bt and isoline plants in row crops can speed the development of resistance of high dose transgenic Bt products, but current rootworm products are not high dose and larval movement and its affects are unknown. We assessed movement of WCR larvae among four configurations of transgenic Bt and isoline plants by infesting specific plants with WCR eggs. Overall, transgenic Bt corn was very effective in controlling WCR. However, when two infested non-transgenic isoline (control) plants surrounded a transgenic Bt plant, a significant number of larvae moved onto the transgenic Bt plant late in the season. These larvae caused significant damage to that transgenic Bt plant and more beetles produced on it than any other plant (including non-transgenic isoline plants) in one year of the study. This plant configuration would occur rarely in a refuge planted with a 5% seed mix and would likely produce beetles of that would be susceptible to the Bt insecticidal protein after completing much of their initial larval development on non-transgenic isoline plants. Movement from transgenic Bt to non-transgenic isoline plants also occurred. This information is important to seed companies, the EPA, and system modelers in their attempts to finalize resistance management plans for transgenic corn.

Technical Abstract: Insect resistance management (IRM) can extend the lifetime of management options, but depends on extensive knowledge of the biology of the pest species involved for an optimal plan. Recently, the Environmental Protection Agency (EPA) registered a seed blend refuge for two of the transgenic Bt corn products targeting the western corn rootworm, Diabrotica virgifera virgifera LeConte. Larval movement between Bt and isoline plants can be detrimental to resistance management for high dose Bt products because the larger larvae can be more tolerant of the Bt toxins. We assessed movement of western corn rootworm larvae among four spatial arrangements of SmartStax® corn (expressing both the Cry34/35Ab1 and Cry3Bb1 proteins) and isoline plants by infesting specific plants with wild type western corn rootworm eggs. Significantly fewer western corn rootworm larvae, on average, were recovered from infested SmartStax plants than infested isoline plants, and the SmartStax plants were significantly less damaged than corresponding isoline plants. However, when two infested isoline plants surrounded a SmartStax plant, a significant number of larvae moved onto the SmartStax plant late in the season. These larvae caused significant damage and produced significantly more beetles than any other plant configuration in the study (including isoline plants) in the first year of the study. This plant configuration would occur rarely in a 5% seed blend refuge and may produce beetles of a susceptible genotype because much of their initial larval development was on isoline plants. Results are discussed in terms of their potential effects on resistance management.