Researchers Say Bt Corn Poses Low Risk to Monarch Butterflies
By Sharon Schmickle
The outcome of these new studies is expected to influence decisions about the varieties that farmers can plant of one of Minnesota's biggest crops. They also provide important information about the well-being of the monarch, which the Minnesota Legislature designated this year as the state butterfly. The researchers stress, however, that their results are preliminary and still under review by other experts. Comparisons of butterfly survival in conventional cornfields and in plots of GM corn turned up no significant differences in Minnesota, Iowa, Maryland, Michigan and southern Ontario near Guelph, scientists said at the workshop organized by the U.S. Department of Agriculture (USDA).
"If there are any differences out there, they aren't very profound," said Richard Hellmich, a USDA research entomologist at Iowa State University in Ames. Indeed, the monarchs fared better at the edges of one Minnesota GM cornfield than they did in a nearby wooded area, said William Hutchison, an entomologist at the University of Minnesota in St. Paul. Likely explanations are that more predators lurked in the woods and that overall conditions were more hospitable in the corn, he said. While reassuring, the findings don't fully erase the concerns that erupted in early 1999 when a study at Cornell University showed that monarch caterpillars died after they were fed GM corn pollen in a laboratory. Scientists said it is important to continue looking for more subtle effects, such as whether the butterflies are weakened or produce smaller progeny after eating pollen from the corn.
One reason for the continued caution is that contrary to assumptions made by government regulators who set rules for the use of the crops the monarchs in the studies seemed to prefer cornfields to other areas for laying eggs. In one Iowa study, the eggs found in cornfields outnumbered those along country roadsides 7 to 1. Minnesota researchers reported similar findings.
Scientists don't quite know the reason why. Karen Oberhauser, a monarch expert at the University of Minnesota, said she won't relax about the possible risk from the crop until the importance of cornfields to monarchs is better understood.
The corn at issue is fortified with genes from a soil bacterium that is lethal to corn borers, a major pest in farm fields. The bacterium, Bacillus thuringiensis (Bt), produces a protein that ruptures cells in the guts of borers, killing the insects. The Bt corn contains the protein throughout the plant and in its pollen.
Humans, other animals and most insects don't have the specific receptors to connect with the protein, so it doesn't affect them.
But because butterflies are closely related to the borers, it can kill them if they eat enough of it. Following reports that butterfly caterpillars did, indeed, die after they were fed Bt pollen in laboratories, the USDA and an industry group awarded $200,000 in grants for studies at several major research universities and private labs. The studies focused on butterflies in the caterpillar stage, when they feed on milkweed plants their sole source of food on which corn pollen might land.
One finding is that pollen rarely collected on milkweed leaves in lethal concentrations, and what did land on the leaves often was washed away by rain or blown off by wind. The concentrations found in the Iowa studies were too low to impose even minor effects on the monarchs, said Hellmich at Iowa State.
The picture that is emerging from that aspect of the research is that "this is not a very big issue," said Eldon Ortman, associate director of agricultural research at Purdue University.
In one Minnesota study near Rosemount, researchers placed potted milkweed plants at the edge of a cornfield, on a strip of soil around the field and close to a nearby wooded area. They monitored caterpillars on the plants and found no significant differences between those near Bt and non-Bt corn, Hutchison said. But they were surprised to find that more caterpillars died near the forest than near the corn. Most of the Midwestern studies focused on field corn, which is used for processing and animal feed. But in Maryland, researchers studied sweet corn, which generally is heavily sprayed with synthetic insecticides as an alternative to Bt corn. They found the caterpillars quickly died in sprayed fields. But in non-sprayed fields, there was no difference between Bt corn and the conventional varieties, said Galen Dively of the University of Maryland in College Park.
Another key question addressed by the studies was whether caterpillars are active in the fields during the two-to three-week period when corn sheds pollen. If not, caterpillars are far less likely to eat the pollen. The answer was "yes" in studies in Minnesota and Ontario. But researchers in Iowa, Maryland and Kansas found little overlap
One finding that cut across all of the studies is that these seemingly delicate butterflies have very tough lives. Insects devour most of the caterpillars. The milkweed they depend upon is sprayed by farmers, trampled by deer and mowed by road maintenance crews. Then, of course, there are the long migratory journeys each year to and from Mexico, where their habitat is dwindling.
Many of the researchers reported losing all or most of the caterpillars in some parts of their projects not to biotech corn but to all of the forces that prey upon them. Among other uses, the researchers' findings will be considered by the U.S. Environmental Protection Agency next year as it reviews requests to renew approval for companies to sell several varieties of Bt corn, cotton and potatoes.
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