1a.Objectives (from AD-416)
The objective of this cooperative research project is to conduct risk assessment research for Lepidopterous pests of Bt-crops. This research should enhance Bt-resistance management strategies which are designed to delay the onset of resistance development in target insects.
1b.Approach (from AD-416)
This agreement will determine the effect of Bt crop production on the population genetics of bollworm, tobacco budworm, and fall armyworm. Specific issues will be:. 1)a better overall understanding of gene flow and population structure for the pests;. 2)Bt-resistance allelic frequency estimates over time;. 3)the impact of changing refuge strategies and dynamic agroecosystems on managing resistance to Bt; and. 4)the impact of Bt-suppressed population densities on insecticide resistance, e.g. the recent pyrethroid resistance in bollworm. The cooperator will be actively involved in all phases of this research including the collection of test insects from across the U. S. Cotton Belt. Pyrethroid resistance assays will be conducted in the cooperator's laboratory. Insect tissue will then be sent to the USDA-ARS for use in genetic marker analysis and carbon isotope analysis. Other technologies (e.g. secondary plant chemical detection in insect tissue and oxygen and nitrogen isotope analysis) will be used as they become available to further understand the population ecology of the pests in relation to Bt resistance management.
To address the overall risk of Bt resistance, this project evaluated the impact of various components within the current cotton belt agricultural landscape. In cooperation with Environmental Protection Agency (EPA), models have been developed to address changes in Bt crops being planted, new Bt events being developed, and changes in Bt-crop refuge requirements being proposed. In particular, models have evaluated the impact of reduced refuges required for multi-gene corn coupled with increased selection pressure on corn earworm (bollworm) on the risk of developing resistance to the Bt toxins. Our model indicates that the risk of resistance from dual-gene corn using similar toxins to those found in Bt-cotton combined with reduced refuges may be somewhat higher than for single-gene corn with a larger refuge. Mixing non-Bt and Bt-plants (refuge in a bag) rather than keeping the refuge and Bt areas distinct further reduces the benefit of the refuge. As the same or similar Bt toxins are being incorporated into corn and cotton, and the crops share some of the same insects, selection for Bt resistance in corn impacts susceptibility in cotton. In addition to the modeling project, we have begun to evaluate the number of volunteer corn plants emerging from corn fields and Bt expression in these plants to understand the risk of additional resistance selection during this autumn generation. We have also begun to measure fitness costs of bollworms developing in Bt corn and their ability to survive and damage Bt and non-Bt cotton. This will give us an indication of the role of selection in Bt corn on survival in Bt cotton when the corn and cotton express similar toxins. ADODR used site visit, email and telephone conferences to monitor activities of the project.