|ANDOW, DAVID - University Of Minnesota|
|PUEPPKE, STEVEN - Michigan State University|
|SCHAAFSMA, ARTHUR - University Of Guelph|
|GASSMANN, AARON - Iowa State University|
|MEINKE, LANCE - University Of Nebraska|
|MITCHELL, PAUL - University Of Wisconsin|
|HURLEY, TERRANCE - University Of Minnesota|
|Hellmich Ii, Richard|
|PORTER, PAT - Texas A&M University|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2015
Publication Date: 2/1/2016
Citation: Andow, D.A., Pueppke, S.G., Schaafsma, A.W., Gassmann, A.J., Sappington, T.W., Meinke, L.J., Mitchell, P.D., Hurley, T.M., Hellmich II, R.L., Porter, P.R. 2016. Early detection and mitigation of resistance to Bt maize by western corn rootworm (Coleoptera: Chrysomelidae). Journal of Economic Entomology. 109:1-12.
Interpretive Summary: Genetically engineered crops producing insecticidal crystal (Cry) proteins from the bacterium Bacillus thuringiensis (Bt) have become a major tool for integrated pest management (IPM) programs. While many Bt traits have been durable, failures of Bt corn rootworm Bt maize to control its target pest, western corn rootworm (Diabrotica virgifera virgifera), have been increasing after field-evolved resistance was first documented in 2011. The unexpectedly rapid development of resistance can be attributed to multiple causes including less than high-dose expression of Bt in maize hybrids, inaccurate assumptions about the biology of western corn rootworm, lengthy delays before recognizing resistance, and increased corn acreage that has resulted in more corn-after-corn plantings instead of crop rotations. Less than high-dose transgenic Bt events are common and present considerable insect resistance management (IRM) challenges, not all of which are scientific or under potential regulatory control. Our experiences provide a warning that IRM strategies based on high dose and refuge may not fit other less than high-dose events, and that adaptive IRM and IPM approaches are needed. We suggest that it is not too late to implement changes in the IRM strategy to preserve the utility of corn rootworm Bt maize by targeting local management earlier in a sequence of responses to the evolution of resistance, developing area-wide criteria to address widespread product failures, and developing programs to counteract economic forces contributing to rapid resistance evolution. These results should be useful to governmental regulators, public-sector scientists and extension entomologists, industry scientists, seed producers, trait providers, and farmers interested in prolonging the benefits of Bt transgenic crops.
Technical Abstract: Transgenic Bt maize that produces less than a high dose has been widely adopted and presents considerable insect resistance management (IRM) challenges. Western corn rootworm, Diabrotica virgifera virgifera LeConte, has rapidly evolved resistance to Bt maize in the field leading to local loss of efficacy for some corn rootworm Bt maize events. Documenting and responding to this resistance has been complicated by a lack of rapid diagnostic bioassays and by regulatory triggers that hinder timely and effective management responses. These failures are of great concern to the scientific and agricultural community. Specific challenges posed by western corn rootworm resistance to Bt maize, and more general concerns around Bt crops that produce less than a high dose of Bt toxin, have caused uncertainty around current IRM protocols. More than 15 years of experience with IRM has shown that high-dose/refuge based IRM is not applicable to Bt events that produce less than a high dose. Adaptive IRM approaches and pro-active, integrated IRM-pest management strategies are needed and should be in place before release of new technologies that produce less than a high dose. We suggest changes in IRM strategies to preserve the utility of corn rootworm Bt maize by 1) targeting local resistance management earlier in the sequence of responses to resistance and 2) developing area-wide criteria to address widespread economic losses. We also favor consideration of policies and programs to counteract economic forces that are contributing to rapid resistance evolution.