CHICAGO (AP) - A new study found that pollen from genetically altered corn poses little risk to monarch butterfly larvae, contradicting previous findings that led to calls to curb the spread of bio-engineered crops.

The larvae digest the pollen when they eat milkweed. A 1999 lab study at Cornell University showing that pollen from the corn could poison larvae caused a public outcry in Europe and rallied environmentalists to demand limits on the crops.    But the latest study, which will be discussed Wednesday at a meeting of the American Chemical Society, found that the larvae usually do not eat enough pollen for it to harm them.

"It's a negligible risk at best. They must consume considerable amounts of pollen to show an effect, and that amount of pollen rarely exists in nature," said Mark K. Sears, chairman of the Department of Environmental Biology at the University of Guelph in Canada.

Sears and a team of scientists looked at how far pollen traveled in a cornfield, if monarch larvae were exposed to it and how much of it the larvae typically ate. The research, funded mostly by the Canadian government, took place on corn fields in Canada, Iowa, Maryland and Minnesota between 1999 and 2000.

The scientists saw no adverse effects except when larvae ate about 4,000 pollen grains. At that point, they began to eat and gain weight more slowly than larvae that ate corn pollen that was not genetically altered.
The symptoms suggested that their stomach linings were breaking down, Sears said.

However, because there is an average of only 120 pollen grains per square centimeter of a milkweed leaf, "it's highly unlikely that larvae are going to be exposed to that much pollen to cause a measurable effect," Sears said. Kevin Steffey, an entomologist at the University of Illinois who was not involved with the study, said Sears' work presents a more accurate study of larvae diets than past research has.

"The questions are, 'Will they eat it in nature?' and 'Are they even going to be exposed to it?' Those questions were not asked in the previous studies," Steffey said.

Gary Rolfe, an ecology professor at the University of Illinois who was not involved with the research, called for more study. The biotech corn was approved for use before enough research was done to show its effects, he said.

"We've rushed to get these varieties out without the ecological work being done," he said. "We just don't have all the answers we need."

Discovery of the biotech corn in taco shells last fall led to nationwide recalls of corn products. The crop's developer was Aventis CropScience, a Research Triangle Park, N.C.-based firm.