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Study: Bt corn benefits other corn

Transgenic corn’s resistance to pests has benefited even non-transgenic corn, a new study led by scientists from the University of Minnesota shows.

The study, published in the Oct. 8 edition of the journal Science, found that widespread planting of genetically modified Bt corn throughout the Upper Midwest has suppressed populations of the European corn borer, historically one of corn’s primary pests. Bt corn, introduced in 1996, is so named because it has been bred to produce a toxin from the soil bacterium Bacillus thuringiensis that kills insect pests.

Led by University of Minnesota Extension entomologist and department head Bill Hutchison and assisted by U-M professor and entomologist Roger Moon, the researchers estimate that farmers in Iowa, Illinois, Minnesota, Nebraska and Wisconsin received cumulative economic benefits of nearly $7 billion from 1996-2009, with benefits of more than $4.3 billion for non-Bt corn farmers alone.

The scientists estimated that in Minnesota, Illinois and Wisconsin borer populations in adjacent non-Bt fields declined by 28% to 73%, with similar reductions recorded in Iowa and Nebraska.

Minnesota benefits most

“Since Minnesota growers were early adopters of the technology, Minnesota looks like it benefited the most,” Moon says.

“We had 50 years of data to look at as a benchmark before Bt corn was introduced in 1996, and then we had 14 years of data [with it],” Hutchison says.

Minnesota has the highest net decline in adjacent non-Bt field borer populations — 73% on average — followed by Illinois, with a 63% reduction, and Wisconsin, with only a 28% reduction. Wisconsin growers also had the slowest adoption rate of Bt technology, the scientists point out.

“The more Bt corn farmers planted, the greater the area-wide reduction,” Moon says.

The researchers attribute the collateral benefits enjoyed by non-Bt farmers to area-wide suppression of corn borers stemming from long-term plantings of Bt-protected corn. Potato, green bean and other host crops also stand to benefit from area-wide reductions of corn borers, the researchers note. However, Hutchison and Moon still caution against planting all corn acres to the Bt technology.

“Farmers need to keep planting susceptible varieties in refuges so susceptible borers will mate and have susceptible offspring,” Moon says. “Refuges are needed for resistance management.”

Initially, planting a refuge was a tough-sell for agronomists and Extension entomologists who told their growers that they still needed to plant non-Bt varieties, too.

“With a 5- to 20-bushel-per-acre loss, growers were saying, ‘I’m not planting corn to support corn borers.’ But now after 14 years, we’ve got a great case study that shows no field level instance of corn borer-developed resistance,” Hutchison says.

The Bt proteins provide the plant with a built-in defense against attacks by the larvae of European corn borers and other insect pests. Larvae that ingest the protein soon stop feeding and die, typically within 48 hours. In addition to reducing the use of insecticides that also can endanger beneficial insects, the Bt defense strategy helps prevent harmful molds from gaining entry to plants via wound sites from borer feeding. Some of these molds, like Fusarium, produce mycotoxins that can diminish the value and safety of kernels.

Last year, Bt corn was planted on nearly 55 million acres in the United States, accounting for nearly 63% of the total U.S. corn crop of 87 million acres. Prior to this study, no research group had investigated the long-term impact of such plantings on corn borer populations on a regional scale, nor had there been any assessment of whether the use of the crop provided any sort of collateral benefit to adjacent or nearby fields of non-Bt crops.

In the U-M, study, participants included researchers from USDA-ARS, University of Wisconsin, Pennsylvania State University, University of Illinois, University of Nebraska, Iowa State University and industry researchers.

USDA-ARS contributed to this report.

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Data crunchers: After looking at 50 years of state corn pest data, plus 14 years of Bt-corn data, U-M’s Bill Hutchison (left) and Roger Moon were able to determine that corn borer populations declined in non-Bt acres.

This article published in the November, 2010 edition of THE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.