Widespread planting of genetically modified Bt corn throughout the Upper Midwest has suppressed populations of the European corn borer, a major insect pest of corn, with the majority of the economic benefits going to growers who do not plant Bt corn, reports a multistate team of scientists in the Oct. 8 edition of the journal Science.
In Wisconsin, 75 percent of the $325 million cumulative economic benefit linked to Bt corn’s pest suppression between 1996-2009 went to non-Bt corn growers. Wisconsin currently has about 3.9 million corn acres, with approximately half in Bt corn.
“This study is the first to estimate the value of area-wide pest suppression from transgenic crops and the subsequent benefit 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 Bt corn acres,” says co-author Paul Mitchell, a University of Wisconsin-Madison agricultural economist who conducted the economic analysis for the study.
Bt corn is genetically modified (GM) to contain a protein from the soil bacterium Bacillus thuringiensis (Bt) that kills insect pests. According to the team’s calculations, the total economic benefit of Bt corn’s pest suppression across Wisconsin, Minnesota, Illinois, Iowa and Nebraska between 1996-2009 adds up to about $6.9 billion. When the team broke the numbers out by Bt and non-Bt fields, they were initially surprised to find that 62 percent of Bt corn’s economic benefit – about $4.3 billion – went to non-Bt corn fields.
On second thought, however, the finding made sense. The primary benefit of Bt corn comes in the form of reduced yield losses, a benefit that Bt corn growers pay for in the form of Bt technology fees. As a result of Bt corn’s area-wide pest suppression, however, growers who plant non-Bt corn in their fields also experience yield savings without the cost of Bt technology fees, and thus receive more than half of the benefits from growing Bt corn in the region.
European corn borer moths cannot distinguish between Bt and non-Bt corn, so females lay eggs in both kinds of fields, explains University of Minnesota entomologist William Hutchison, the study’s chief author. 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 the 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 area-wide reduction in corn borer abundance.
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. “Additionally, environmental benefits from corn borer suppression are likely occurring, such as less insecticide use, but these benefits have yet to be documented,” says Hutchinson.
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.
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 study shows that Bt corn is more valuable to society than originally realized, which makes maintaining its effectiveness even more important.