Submitted to: Ecological Applications
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/15/2009
Publication Date: 7/1/2010
Citation: O'Rourke, M.E., Sappington, T.W., Fleischer, S.J. 2010. Managing Resistance to Bt Crops in a Genetically Variable Insect Herbivore, Ostrinia nubilalis. Ecological Applications. 20(5):1228-1236. Interpretive Summary: Transgenic Bt (Bacillus thuringiensis) corn is very effective in preventing damage and economic loss caused by the European corn borer (ECB), a chronically destructive moth pest throughout most corn-growing areas of the U.S. However, there is concern that ECB will develop resistance to the Bt toxin because so many farmers plant it. To prevent or delay resistance development, growers are required to plant a certain percentage of their corn acreage to non-Bt corn as a nursery for susceptible ECB to mate with any resistant ECB that might emerge from the Bt corn. Because ECB can feed on other kinds of plants besides corn, it has been suggested that moths emerging from this "unstructured" refuge might be enough that the percentage of required non-Bt corn "structured" refuge could be reduced or eliminated. By using a technique that measures the form of carbon in the larval diet typical of corn or non-corn plants the larvae fed on, we found that one race of ECB (called "E race") where females produce a particular form of male-attractant pheromone ("E pheromone") does produce a relatively substantial proportion of adults from non-corn host plants. However, the other kind of ECB, the Z race, is produced almost entirely on corn. Thus, even though unstructured refuge might be possible for the E race, it is not possible for the Z race. Because we found that in every county where the E race occurs, the Z race also occurs, our study does not support a relaxation of the current refuge requirements for ECB. The results of this study will be used by regulatory agencies, biotech seed industry scientists, and other government and university scientists in the U.S., Europe, and Asia who conduct research on insect resistance management, and who are involved in developing, recommending, or implementing improved refuge requirements for Bt corn.
Technical Abstract: The "high-dose/refuge strategy" is central to the insect resistance management (IRM) plan adopted by the United States Environmental Protection Agency (EPA) to slow resistance evolution of European corn borer (ECB-Ostrinia nubilalis) to transgenic Bacillus thuringiensis (Bt) corn and organic Bt insecticides. For polyphagous insects such as ECB, there is potential to substitute unstructured (non-corn) refuges for structured non-Bt corn refuges. However, there is debate over the contribution of unstructured refuges to ECB populations. In this research we use stable carbon isotope analysis of adult ECB from upstate New York to determine the percentage of populations that develop in unstructured refuges. We further examine other ecological factors important to refuge design including: separate rates of unstructured refuge use for the E and Z pheromone races, physiological consequences of developing on non-corn hosts, and the ranges of the two pheromone races. We found that the average rate of development in unstructured refuges was significantly higher for E (18%) than Z race ECB (4%). However, feeding on non-corn hosts is related to decreased body mass, which relates to lower fecundity for female, Z race ECB. Data also show that the range of Z race ECB completely overlaps that of the E race. While the rate of E race ECB developing in unstructured refuges is higher than previously assumed, low rates of unstructured refuge use by the Z race, complete sympatry within the E race range, and evidence for reduced fecundity of adults reared on non-corn hosts, all argue against a relaxation of current IRM refuge standards based on alternative host use by this species.