New Biotech Test for Cotton Pests

A new test could let cotton farmers reduce their spraying of pyrethroids. Or it could also help keep these insecticides useful when needed, if no other alternatives are available.

Tobacco budworms, Heliothis virescens, and their cotton bollworm cousins, Helicoverpa zea, cost southeastern cotton farmers several hundred million dollars a year in damage and chemical controls. Farmers normally control the pests with pyrethroids, which are inexpensive and relatively nontoxic to vertebrates. But the more they use a pyrethroid against budworms, the sooner it "runs out of gas."

That's because the budworm--unlike the bollworm--becomes increasingly resistant to pyrethroids during the growing season.

"Resistance starts low and builds, and it is higher in cotton-growing areas," says Matthew H. Greenstone, an entomologist with the Agricultural Research Service. He's at ARS' Plant Sciences and Water Conservation Research Laboratory in Stillwater, Oklahoma.

"A lot of wasteful, resistance-promoting, and expensive spraying could be avoided by differentiating the two pests at a very early stage," says Greenstone.

Doing this isn't practical now, but it may be in a few years. Greenstone has developed and patented a monoclonal antibody that distinguishes between the pests at the egg stage.

"The antibody binds to the egg protein of the bollworm but not to that of the budworm, so the test is unequivocal," he says.

Greenstone is looking for commercial developers to package the new test in a field kit. "This would enable scouts to determine the proportion of eggs of each species in a sample in just a few minutes," he says. With that information plus total egg counts, farmers could make a speedy decision on whether to spray.

For example, if the proportion of budworm eggs was high, pyrethroids might be advised, provided that total eggs--and budworm resistance--were low. Otherwise, the best strategy might be a combination of different chemical insecticides and biopesticides such as Bacillus thuringiensis.

"Widespread use of an egg test kit would reduce pyrethroid sprays, while prolonging their useful life," he says. "Furthermore, using less insecticide overall would conserve the pests' natural enemies, further cutting the need for insecticides."--By Hank Becker, Agricultural Research Service Information Staff.

Matthew H. Greenstone is at the USDA-ARS Plant Sciences and Water Conservation Research Laboratory, 1301 N. Western St., Stillwater, OK 74075; phone (405) 624-4119, fax (405) 372-1398.

"New Biotech Test for Cotton Pests" was published in the June 1998 issue of Agricultural Research magazine. Click here to see this issue's table of contents.