09/10/1997

Entomologists at AU Helping Alabama Take the Lead in Bt Cotton Resistance Monitoring

AUBURN, Ala. - In 1996 and 1997, Alabama led the country in acres of Bt cotton planted, and beginning this year, the state will be a leader in insect resistance monitoring in cotton, said William Moar, associate professor of entomology in Auburn University's College of Agriculture.

Last year, U.S. cotton growers planted 1.8 million acres of Bt cotton, which is genetically engineered to contain a Bacillus thuringiensis protein that is toxic to the tobacco budworm, cotton bollworm and pink bollworm. Bt cotton has already proven that it can reduce pesticide use and bring higher yields, said Ron Smith, extension entomologist and professor of entomology.

Resistance is a significant concern with Bt cotton because insects are exposed to the insecticide within the plant from the time it emerges from the soil until the end of the growing season, Moar said.

"The resistance issue is much greater with transgenic plants than with chemical pesticides. The more you expose insects to a controlling agent, the more you are selecting for resistance to that agent because you are killing everything except those organisms that are resistant," Moar said.

Though Bt cotton has only been available for two growing seasons, Smith said it's best to start monitoring for resistance early to establish a standard for comparison for the next several years.

"Insects have a great ability to adapt," Smith said. "It's important that Alabama take the lead in monitoring because we've planted the highest percentage of Bt cotton acres of any state." In 1996, Alabamians planted 400,000 acres of Bt cotton.

Two precautionary options against resistance are built in to the use of Bt cotton. With the first option, growers must plant at least four percent non-Bt cotton, which they will not spray with any pesticides. The second option is to plant 20 percent non-Bt cotton, which can be sprayed with any pesticide that is not Bt related.

These precautions should keep a healthy population of Bt susceptible insects around to mate with resistant insects, ensuring that the dominant susceptibility will prevail in the next generation.

"What we're guarding against and monitoring for is how fast the insects are going to adapt," Smith said.

Resistance monitoring and management are required by the Environmental Protection Agency, and the U. S. Department of Agriculture (USDA) is sponsoring a program to study insects that "escape" the toxic cotton.

"Resistance is a major issue," Moar said. "Because of the tremendous impact and concern, all of the cotton growing states are doing this."

Each state is responsible for developing their own method of collecting caterpillars, and people in the cotton industry in Alabama have been enthusiastic about helping with this program, Moar said.

Moar designed a kit that includes insect cups with food, a description sheet, an ice pack and a shipping container. He estimates that about 50 kits will be sent to consultants, county agents and growers in different parts of the state.

Once growers have collected the surviving caterpillars from Bt-treated cotton fields, they are sent to the USDA lab in Stoneville, Miss. Researchers then raise the caterpillars to adult moths and mate them to screen the next generation for resistance to Bt.

Moar expects most of the escapes to be cotton bollworm because Bt works best at controlling tobacco budworm. Bt cotton is still 75 percent effective against cotton bollworm, Smith said, but bollworm pressures have been especially high in certain areas this year.

Smith doesn't expect resistance to become a problem for four or five years, and he hopes that by then, new varieties of Bt cotton will be developed to combat developing resistance.

"It's a race to keep the technology ahead of a very adaptable animal," Smith said.

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News from:

Office of Ag Communications & Marketing

Auburn University College of Agriculture
Alabama Agricultural Experiment Station
3 Comer Hall, Auburn University
Auburn, AL 36849
334-844-4877 (PHONE) 334-844-5892 (FAX)

Contact Jamie Creamer, 334-844-2783 or jcreamer@auburn.edu
by Anna M. Lee

September 10, 1997