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United States Department of Agriculture

Agricultural Research Service


Location: Southern Insect Management Research Unit

2012 Annual Report

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. Landscape population models of Lygus lineolaris and Helicoverpa zea will be adapted from existing Bt-resistance evolution models to organize information and prioritize research on polyphagous pests impacting the economics and ecology of Bt cotton systems in the Mississippi Delta.

3.Progress Report:

The bollworm (corn earworm) is a major pest target of Bt toxins in corn and cotton. In both crops, the insect is targeted with similar Bt toxins, so successive generations of this pest are potentially exposed to the same selection pressure. We are assessing this risk in several ways.

A major thrust of field research during the last 12 months has been to examine the role of volunteer corn on the evolution of resistance of the bollworm. We are undertaking several studies to examine this aspect of Bt resistance risk. We conducted a survey of corn fields after harvest to assess the density and maturity of volunteer corn in the fall as well as the abundance of corn earworm in non-Bt corn at various growth stages. We have also conducted greenhouse and field trials examining the efficacy of various crosses of Bt and non-Bt corn varieties on bollworm. These trials are being repeated during 2012. We are also evaluating the change in performance on cotton of bollworms that developed on Bt corn varieties compared to non-Bt corn varieties. We are conducting bioassays of various crosses of these bollworm populations to try to determine the genetic basis of differences in performance and are continuing these studies during 2012.

A second method for assessing the risk of resistance development in corn earworm is through computer modeling. We have continued to use and modify a computer model to address the risk of resistance that comes from changes in our agricultural landscape and the Bt technologies available to farmers. In addition to the modeling, we have invested in improving the user interface for the model. This will allow more people to use the model and adjust the parameters for the insect or technology of interest without compromising the integrity of the underlying program.

Last Modified: 4/18/2014
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