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Corn-Pest Resistance Study Sees Need for Larger Refuge

Corn farmers planting genetically modified crops should use larger areas of conventional grain to slow the western corn rootworm beetle’s development of resistance to the modified plants’ insect-repelling traits, researchers said.

The U.S. Environmental Protection Agency should more than double the area it requires farmers to plant with regular corn, Bruce Tabashnik from the University of Arizona and Fred Gould from North Carolina State University wrote in the June issue of the Journal of Economic Entomology.

Corn is made to produce proteins that are toxic to some insect pests by adding a gene from the soil bacterium Bacillus thuringiensis, or Bt. Insects can evolve resistance to Bt just as they can to regular insecticides, the University of Arizona wrote in an online statement.

“We’re seeing the early signs of rootworm resistance to Bt corn, which fit predictions from evolutionary theory and experiments in the lab and greenhouse,” Tabashnik, head of the entomology department at the University of Arizona’s College of Agriculture and Life Sciences, was cited as saying.

EPA rules require farmers that sow biotech corn producing one Bt protein to plant 20 percent of acreage with conventional corn as a so-called refuge area, while those planting corn producing two Bt proteins must plant a refuge area of 5 percent, according to the statement.

For Bt corn to remain effective against rootworms, the refuge requirements should be raised to 50 percent and 20 percent, respectively, according to Tabashnik and Gould. Rootworm resistance against Bt corn was first found in Iowa in 2009, according to the statement.

“A single farm can have millions of these beetles,” Tabashnik said. “If 1 percent to 6 percent survive on Bt corn, you have tens of thousands of potentially resistant insects and the refuge needs to be much bigger.”

To contact the reporter on this story: Rudy Ruitenberg in Paris at

To contact the editor responsible for this story: Claudia Carpenter at

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