Field refuges prevent moth's resistance to genetic insecticides

March 02, 2000

ITHACA, N.Y. -- Cornell University scientists have demonstrated that creating a refuge in a crop field reduces the chance of insects developing resistance to transgenic insecticidal plants. Researchers report on their finding in the current (March) issue of the journal Nature Biotechnology.

"The whole concept of a refuge really works," says Anthony M. Shelton, Cornell professor of entomology and the lead author on the Nature Biotechnology article. "Before it has been theory, and this is the first demonstration of it in a field situation. This is all about managing resistance, and we found that, yes, it is important to have a refuge and to manage those insects within the refuge carefully."

In this case, a refuge is a section of plants within the field that have not been genetically engineered to contain the insecticide.

The insecticide contained in the plants is Bacillus thuringiensis (Bt), a naturally occurring bacterium that is not harmful to humans and is considered by the Environmental Protection Agency (EPA) as the safest insecticide from an environmental standpoint. The genes to produce Bt proteins have been engineered into plants, and last year farmers in the United States planted nearly 19 million acres of transgenic Bt crops approved by the EPA.

"Bt transgenic plants can greatly reduce the use of broader spectrum insecticides, but there is concern that this technology may be short-lived due to insect resistance," writes Shelton in the Nature Biotechnology article. Shelton and his colleagues conducted field tests to examine ways of reducing the likelihood of the diamondback moth developing resistance to Bt broccoli plants.

At Cornell's New York State Agricultural Experiment Station in Geneva, N.Y., the scientists had previously conducted laboratory and greenhouse trials for several years using Bt broccoli plants engineered by Elizabeth Earle, Cornell professor of plant breeding and chair of the university's plant breeding department. "Once we felt comfortable with our system, it was important to take it to the field to see how a resistance management program would work under field conditions," says Shelton.

To manage resistance to Bt-engineered plants, Shelton and his colleagues examined several planting options, including how the refuge was placed in the field. Their findings are clear -- a refuge is needed, but it is also important how that refuge is placed. Using a "20 percent mixed refuge," in which the Bt and non-Bt plants were mixed randomly, compared with a "20 percent separate refuge," in which a block of non-Bt plants was grown next to the Bt plants, they followed changes in the insects' level of resistance over the course of the season. Their results backed up theoretical models that indicated a separate refuge would be more effective in keeping the diamondback moth from becoming Bt-resistant.

Additional studies examined how to manage the insects in the refuge. The studies' results demonstrated the importance of making sure sufficient insects are generated on the non-Bt plants to mate with any resistant insects that may have survived on the Bt plants.

Fred Gould, professor of entomology at North Carolina State University, a noted expert in the use of Bt transgenic plants, says in an accompanying commentary in the journal, "Field studies like this one are essential for developing public confidence in resistance management techniques."

Joining Shelton and Earle in authoring the article, "Field Tests on Managing Resistance to Bt-Engineered Plants," are Juliet Tang, a former Cornell entomologist now at Mississippi State University; Richard Roush, a former Cornell entomologist now at the Waite Institute in Australia; and Timothy D. Metz, a former Cornell plant breeder now at Campbell University in North Carolina. The U.S. Department of Agriculture funded the research.

Cornell University

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