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Benefits of Bt

October 7, 2010

Corn borer on ear of corn.

Controlling the European corn borer with Bt corn reduces pest damage in non-Bt corn too, a U of M study indicates.

Growers of non-Bt corn reap savings from Bt cornfields, study shows

By Deane Morrison

Fields of corn engineered to resist insect pests has allowed non-engineered cornfields to save farmers in Minnesota and four other Corn Belt states more than $4 billion over 14 years, a new U of M study shows.

The work is published in the October 8, 2010, issue of Science.

For the past 14 years, Corn Belt farmers have been planting "Bt" corn engineered to produce insect-killing proteins isolated from the bacterium Bacillus thuringiensis. The main target is the European corn borer, which causes an estimated $1 billion in damage every year.

Because Bt corn effectively kills the larvae of corn borers, it reduces the population of adult moths available to infest the next crop of either Bt or non-Bt corn.

In the current study, University of Minnesota entomology professor William Hutchison, with colleagues at the U of M and several other institutions, examined data from Iowa, Illinois, Nebraska, and Minnesota—the top four corn-growing states, with 2009 yields valued at $27.1 billion—and Wisconsin. The researchers used data on corn borer numbers and annual USDA data on yield, price, and planted area to estimate benefits for both Bt and non-Bt corn growers for the last 14 years.

They estimated that together, non-Bt corn growers in Illinois, Minnesota, and Wisconsin realized more than $2.4 billion in savings from suppression of corn borer populations in Bt cornfields over that time period. For Iowa and Nebraska, the savings were $1.9 billion. Total non-Bt corn savings: nearly $4.3 billion.

Looking at Minnesota, Illinois and Wisconsin, the study also found that the higher the percentage of fields that were planted with Bt corn, the lower the density of corn borer larvae on the plants in that state.

"Although many factors are known to affect [corn borer] population dynamics, including weather and natural enemies, these results indicate that reductions in [corn borers] were associated with commercialization of Bt maize," says Hutchison.

Fields planted only with Bt corn would exert strong pressure on the corn borer to evolve resistance to the Bt insecticides. Therefore, the EPA has mandated that a certain percentage of corn be non-Bt, to provide a refuge where corn borers can reproduce and provide a steady supply of individuals susceptible to Bt circulating in the population.

So the benefits are actually mutual: Bt corn kills corn borers, which helps non-Bt growers in a region, and non-Bt cornfields help slow down the evolution of resistance to Bt, extending its lifetime as a useful means of controlling the pest.

Also, say the researchers, because the corn borer eats many other crops, the results suggest that farmers growing other non-Bt crops might also benefit from Bt corn plantings in their region.

But sustaining the economic and environmental benefits of planting Bt corn depends on "continued stewardship by producers to maintain non-Bt [corn] to minimize the risk of evolution of Bt resistance in crop pest species," among other factors, the researchers note.

Tags: College of Food, Agricultural and Natural Resource Sciences