UNIVERSITY PARK, Pa. — Transgenic corn‘s resistance to pests has benefited even nontransgenic corn, according to agricultural researchers and entomologists.
The researchers 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 area-wide 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, has been bred to produce a toxin from the soil bacterium Bacillus thuringiensis (Bt) that kills insect pests.
The researchers reported their results in a recent edition of Science. Implications of planting more genetically modified Bt corn in Pennsylvania are less clear, but researchers are encouraged by their findings in the Midwestern states.
Corn borer moths cannot distinguish between Bt and non-Bt corn, so females lay eggs in both kinds of fields, said 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, Bt corn has been adopted on about 63 percent of all U.S. corn acres. As a result, corn borer numbers also have 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 researchers also documented similar declines of the pest in Iowa and Nebraska.
This is the first work to show a direct association between Bt corn use and an area wide reduction in corn borer abundance.
“In Pennsylvania we have a more complex population structure than in the Midwest,” said co-author Shelby J. Fleischer, professor of entomology in Penn State’s College of Agricultural Sciences.
“We have two pheromone-biotypes of European corn borer in Pennsylvania, but the Midwest has only one.” Fleischer notes that the project focused on the type of corn borer that overwhelmingly develops on corn, but that the other biotype in Pennsylvania may lay eggs and develop on other plants 10 to 15 percent of the time.
“In our area, we need to better determine where Bt-corn is being planted and see how that affects both types of corn borer,” said Fleischer. “We then need to look at how that influences economics and pest management.”
Economic benefits of this area wide pest suppression have totaled $6.9 billion over the past 14 years for the five Midwestern states. 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 area wide 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 co-author of the study, emphasized that “previous cost-benefit analyses focused directly on transgenic crop acres. This is the first study to include the value of area wide 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 U.S. and the world, but those benefits cannot be documented without adequate data.
“My expectation is that if we collect data in Pennsylvania, we will see area wide reductions in corn borer in Pennsylvania as we did in the Midwestern states, but with greater variation at this point in time,” said Fleischer.
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 USDA, several state departments of agriculture and the Rapid Agricultural Response Fund, University of Minnesota funded this work.
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