Genetically modified crop resistance to pests benefits non-modified crop, U of Minnesota study finds

(Press-News.org) Transgenic corn's resistance to pests has benefitted 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. This areawide suppression has dramatically reduced the estimated $1 billion in annual losses caused by the European corn borer, even on non-genetically modified corn. Bt corn, introduced in 1996, is so named because it has been bred to produce a toxin from the soil bacterium Bacillus thuringiensis (Bt) that kills insect pests.

Corn borer moths cannot distinguish between Bt and non-Bt corn, so females lay eggs in both kinds of fields, said the study's chief author, University of Minnesota entomology professor William Hutchison. Once eggs hatch in Bt corn, young borer larvae feed and die within 24 to 48 hours. Because it is effective at controlling corn borers and other pests, Bt corn has been adopted on about 63 percent of all U.S. corn acres. As a result, corn borer numbers have also declined in neighboring non-Bt fields by 28 percent to 73 percent in Minnesota, Illinois and Wisconsin, depending on historical pest abundance and level of Bt-corn adoption. The study also documents similar declines of the pest in Iowa and Nebraska. This is the first study to show a direct association between Bt corn use and an areawide reduction in corn borer abundance.

Economic benefits of this areawide pest suppression have totaled $6.9 billion over the past 14 years for the 5-state region. Surprisingly, non-Bt corn acres accounted for $4.3 billion (62 percent of this total benefit.) The primary benefit of Bt corn is reduced yield losses, and Bt acres received this benefit after the growers paid Bt corn technology fees. But as a result of areawide pest suppression, non-Bt acres also experienced yield savings without the cost of Bt technology fees, and thus received more than half of the benefits from growing Bt corn in the region.

Paul Mitchell, an agricultural economist at the University of Wisconsin-Madison, and a co-author of the study, emphasized that "previous cost-benefit analyses focused directly on transgenic crop acres. This study is the first to include the value of areawide pest suppression and the subsequent benefits to growers of non-transgenic crops. In this case, the value of the indirect yield benefits for non-Bt corn acres exceeded the net value of direct benefits to the Bt corn acres." The authors note that their analysis does not consider benefits for other important Midwestern crops affected by European corn borer, such as sweet corn, potatoes and green beans. Hutchison observed however, "that additional environmental benefits from corn borer suppression are likely occurring, such as less insecticide use, but these benefits have yet to be documented."

The authors were able to document the suppression of European corn borer in Minnesota, Illinois and Wisconsin because state entomologists have monitored pest populations for more than 45 years in those states. Pest suppression and similar benefits to adopters and non-adopters alike may be occurring as a result of the widespread use of transgenic insect-resistant crops in other parts of the United States and the world, but those benefits cannot be documented without adequate data.

Finally, the authors emphasize that sustaining the economic and environmental benefits of Bt corn and other transgenic crops for adopters and non-adopters alike depends on the continued stewardship of these technologies. Farmers, industry, and regulators need to remain committed to planting non-Bt corn refuges to minimize the risk that corn borers will develop resistance to Bt corn. The Science magazine study shows that Bt corn is more valuable to society than originally realized, which makes maintaining its effectiveness even more important.

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