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Insect resistance to Bt crops: evidence versus theory


Evolution of insect resistance threatens the continued success of transgenic crops producing Bacillus thuringiensis (Bt) toxins that kill pests. The approach used most widely to delay insect resistance to Bt crops is the refuge strategy, which requires refuges of host plants without Bt toxins near Bt crops to promote survival of susceptible pests. However, large-scale tests of the refuge strategy have been problematic. Analysis of more than a decade of global monitoring data reveals that the frequency of resistance alleles has increased substantially in some field populations of Helicoverpa zea, but not in five other major pests in Australia, China, Spain and the United States. The resistance of H. zea to Bt toxin Cry1Ac in transgenic cotton has not caused widespread crop failures, in part because other tactics augment control of this pest. The field outcomes documented with monitoring data are consistent with the theory underlying the refuge strategy, suggesting that refuges have helped to delay resistance.

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Figure 1: Field-evolved resistance of Helicoverpa zea to Bt cotton demonstrated by increases in the median lethal concentration (LC50) of the Bt toxin Cry1Ac for field populations.
Figure 2: Simulated effect of refuge abundance (%) on pest resistance to Bt crops.


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We are especially grateful to R. Luttrell, A. Mathias, W. Moar, D. Onstad, M. Sisterson and K. Wu for comments and suggestions. This work was supported by the National Research Initiative, the Cooperative State Research, Education, and Extension Service, and United States Department of Agriculture grant 2006-35302-17365.

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Correspondence to Bruce E Tabashnik.

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Although the preparation of this article was not supported by organizations that may gain or lose financially through its publication, the authors have received support for other research from Monsanto Co. and Cotton Incorporated. In addition, one of the authors (B.E.T.) is a coauthor of a patent application on engineering modified Bt toxins to counter pest resistance, which is related to published research (Science 318, 1640–1642, 2007).

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Tabashnik, B., Gassmann, A., Crowder, D. et al. Insect resistance to Bt crops: evidence versus theory. Nat Biotechnol 26, 199–202 (2008).

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