Bollworms develop resistance

Published 11:58 pm Sunday, March 2, 2008

NATCHEZ — A recently published study suggests that bollworms are developing a resistance to a common pest control method.

Bt-cotton is a genetically engineered plant that produces the toxin Bacillus thuringiensis, which is deadly to several cotton pests.

After analyzing tests from Australia, China, Spain and the United States, University of Arizona researcher Bruce Tabashnik concluded that the American cotton bollworm — or, scientifically, Helicoverpa zea — has begun to evolve a resistance to the toxin as it exists in the genetically engineered cotton.

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Some of the plots where Tabashnik said bt-resistant bollworms were observed were in Mississippi.

There’s no reason to panic if the bollworms have developed the resistance, Tabashnik said.

“There are other control methods for bollworms such as conventional pesticides,” he said.

The problem is that the engineered plants were developed to ease the use of pesticides.

“The reason these plants were developed was to reduce the use of pesticides, but that’s not an area of major concern,” Tabashnik said.

For Concordia Parish farmer Buddy Tanner, who has used the engineered cotton since it first became available approximately 12 years ago, there’s not a lot of concern about the bt-resistant bollworms at this point.

“They’re still a good distance away,” Tanner said.

And Tanner said if the bt-resistant bollworms made their way into the area he would just have to use more pesticides.

“We’re trying to move away from that because pesticides are expensive and can be harmful to the environment,” Tanner said.

MSU-cotton entomologist Angus Catchot said he has not yet encountered the bt-resistance at a field level, and even Tabashnik noted in his research that some researchers thought that a low susceptibility to the bt-cotton was just a natural variance within the bollworm population.

“The bt-cotton has never been that good at controlling the bollworms at the reproductive stage anyway,” Catchot said.

But if the caterpillars are developing a resistance to the toxin, other major pests it targets are not.

“There are five other major pests that are not showing any resistance (to the bt-cotton),” Tabashnik said.

The bollworm — also commonly known as the corn earworm and the tomato fruitworm — is a caterpillar that consumes cotton bolls. As an adult, Helicoverpa zea is a moth.