As the corn growing season nears its end, farmers aren’t the only ones reflecting on the fruits of their labor. Scientists have also spent the summer in cornfields, but for a different reason: They’re trying to find out if genetically modified foods are harmful to the environment.

The controversy over biotech crops is sure to be fueled by a new study from researchers at Iowa State University. Their findings confirm an earlier study showing that pollen from genetically modified corn can kill insects it wasn’t intended to harm—like the beautiful and threatened Monarch butterfly.

Weeds and caterpillars

The study, published August 19^th in the online version of the journal Oecologia, is likely to become a weapon in the arsenal of those opposing genetically modified foods. It deals with the effect of pollen from genetically modified corn. This pollen can make its way to milkweed eaten by Monarch butterfly caterpillars, and kill the Monarchs."The big question we answered was what are the densities of pollen landing on milkweed plants in and near cornfields, and also showing that those densities can have a negative effect on the Monarch butterfly," says Laura Hansen, an entomologist who was one of the study’s authors.

Hansen and fellow entomologist John Obrycki studied Bt corn, which is genetically engineered to produce a natural toxin called Bacillus thuringiensis. Bt is fatal to European corn borers, pests that plague corn crops in North America.

The researchers placed potted milkweed plants in and around fields containing different types of Bt corn. Then they counted the pollen on the leaves and went back to the lab to test the impact that amount of pollen would have on the caterpillars.

After 48 hours of exposure to pollen containing a relatively high amount of toxin, 50 percent of the caterpillars died within five days. When caterpillars were exposed for the same amount of time to pollen that had less toxin, 38 percent of them died within five days.

"From our findings, I believe that Monarch larvae feeding within the cornfield during pollen shed [when the pollen is coming off the corn and blowing in the wind], that it’s probably going to have an effect on those larvae," says Hansen. But other scientists have issues with the study.

"What they did does not accurately reflect or measure conditions that are really present in nature that Monarch larvae are likely to experience," says Val Giddings, vice president for food and agriculture for the Biotechnology Industry Organization.

Giddings maintains that although the study has been billed as a field study, certain aspects of it aren’t. "What you’ve got to do is you’ve got to demonstrate some mortality at the level of exposure that one really finds in nature with the concentrations of pollen that Monarch larvae are actually likely to run into," he says. "And you’ve got to do it under circumstances where wind and rain are free to reduce the amount of pollen on the milkweed leaves, where the Monarch larvae have the freedom to eat something other than the pollen-dusted leaves."

Adding fuel to the fire

The Iowa study follows another controversial study by scientists at Cornell University published in May 1999 in the journal Nature. It was in the Cornell study that researchers announced that Monarch butterfly caterpillars died from eating milkweed leaves dusted with Bt corn pollen. But the study was criticized because it took place entirely in the laboratory, not the field, so it may not have taken into account how much pollen the caterpillars would have actually been exposed to.

But last spring, researchers the University of Illinois published a field study in the Proceedings of the National Acadamy of Sciences about the effects of Bt corn on black swallowtail caterpillars. This study found that the black swallowtails weren’t harmed by a type of Bt corn widely planted in the U.S.

The Cornell study sparked interest in researching the effect of Bt corn on wildlife. Giddings says some 20 other field studies that contradict the Iowa study are now underway. Normally, however, two growing seasons are required before the results are examined. The Iowa researchers began their study one year before the Cornell report appeared, so they had a head start on the current research, which is largely funded by the U.S. Department of Agriculture and the Environmental Protection Agency. Results are expected within the next year.

Meanwhile, many growers as well as scientists insist that Monarch caterpillars don’t really run into Bt pollen on milkweed in or near cornfields. "In the real world where we live, 90 percent of the pollen comes out of the corn plant before the Monarch is even out, so all of that pollen is out before the Monarch is," says Rod Pierce, a farmer who has been planting Bt corn for the past three years. Also, he says, "We feel the milkweed—most farmers consider it a weed and we use herbicides to eradicate it from our crop areas. There are milkweeds in road ditches and other non-crop areas and we feel that’s a good habitat for the Monarch."

The Monarch population is expected to decrease this year, according to Chip Taylor, director of Monarch Watch and an entomology professor at the University of Kansas. "Whether it’s due to Bt corn is impossible to assess," he says. Last year the overwintering population was 100 million, while the previous year it was 60 million, according to Taylor. "But if we hadn’t had Bt corn out there we may have had 140 million," he says.

While the number of Monarchs is down, so is the acreage of biotech corn planted in the corn belt. The fact that it’s impossible to correlate these statistics is heating up the debate over biotech foods. What’s more, even Hansen says it’s unclear how many Monarch butterflies emerge from cornfields in the first place. So even if Bt can harm them, how much of an effect it has on the Monarch population remains to be seen.

Elsewhere on the web:

American Corn Growers Association

Monarch Butterflies and Bt Corn, from BIO