A popular new variety of corn plant that has been genetically modified to resist insect pests may also be taking a toll on the monarch butterfly, one of the most beloved insects in the United States, new research suggests.
The gene-altered corn, which exudes a poison fatal to corn-boring caterpillars, was introduced in 1996 and now accounts for more than one-quarter of the nation's corn crop much of it in the path of the monarch's annual migration.
Pollen from the plants can blow onto nearby milkweed plants, the exclusive food upon which monarch larvae feed, and get eaten by the tiger-striped caterpillars. In laboratory studies at Cornell University, the engineered pollen killed nearly half of those young before they transformed into the brilliant orange, black and white butterflies so well known throughout North America.
Several scientists expressed concern yesterday that if the new study's results are correct, then monarchs which already face ecological pressures but have so far managed to hold their own may soon find themselves on the endangered species list. Other butterflies also may be at risk.
Other scientists, however, criticized the research as seriously flawed and said butterflies would probably suffer more if farmers went back to their old chemical sprays.
Whatever the actual ecological impact, the monarch's popularity is likely to put pressure on the already embattled agricultural biotechnology industry and on the Environmental Protection Agency (EPA), which approved the crops.
"It's sort of the Bambi of the insect world," said Marlin Rice, a professor of entomology at Iowa State University in Ames. "It's big and gawdy and gets a lot of good press. And you've got school kids all across the country raising them in jars."
The corn in question is one of five varieties that will be planted on about 22 million U.S. acres this year. It contains a bacterial gene called Bt, which makes a chemical deadly to European and Southwestern corn borers, caterpillars that mine into cornstalks and destroy developing ears before maturing into moths. The borers cause $1 billion worth of damage annually.
Bt corn already is under fire because of concerns that widespread planting may speed the development of pests resistant to Bt sprays, which are harmless to people and cherished by organic farmers. Cornell entomologist John E. Losey was looking into that issue when he noticed that the milkweed near his test plots was heavily dusted with corn pollen. That made him wonder whether Bt pollen might be killing monarchs or other "non-target" butterflies and moths beyond the boundaries of farmers' fields.
Losey and co-workers sprinkled Bt pollen on milkweed leaves and allowed monarch larvae to feed on them. Within four days, 44 percent were dead. The rest were small and lethargic. Larvae that were fed conventional pollen did fine, they report in today's issue of the journal Nature.
"I think these findings are very worrisome," said Linda S. Rayor, who worked with Losey. "It seems to me it has the potential for a very large population effect on the monarchs."
And although the work was confined to a laboratory, Rayor said, ongoing field experiments by scientists in Iowa are generating similar results.
Monarchs migrate from Mexico and Southern California to northern states in spring, and their progeny return south in the fall. About half of the monarchs that winter in Mexico grow up as caterpillars in the U.S. corn belt, feeding on milkweed around the edges of fields. Corn pollination occurs while these larvae are feeding.
Farmers sprayed Bt for years before Bt-exuding corn was available, but concentrations were lower and fewer acres were sprayed than currently are planted with Bt corn, said David Andow, a University of Minnesota insect ecologist who said he is concerned about the new findings. "In Europe," he said, "where the landscape is even more finely divided and where endangered species are closely associated with agricultural landscapes, it will be even more important to look at the relationship between native butterfly species and Bt corn."
Some experts criticized the EPA, which is already being sued by environmentalists for alleged shortcomings in its ecological risk assessment for Bt corn. The agency demands evidence from companies that new varieties will not directly harm beneficial species, such as honeybees. But it does not require tests for "second tier" organisms that might eat those species, or for species such as monarchs that simply live nearby.
"All of this is adding up to show that EPA does not have a program to protect against these risks and is not in a position to detect these kinds of problems," said Jane Rissler, a senior staff scientist at the Washington-based Union of Concerned Scientists.
EPA officials said they were conducting a formal review of the new data and would release a report when they were done.
Other experts, however, criticized the Cornell researchers for not actually measuring Bt doses in the study, and ventured that Bt probably ranks low compared with other monarch threats. "I don't think it's a very big issue," said Rice of Iowa State. Much of the monarch's habitat was lost when tall-grass prairies were converted to farmland, he said, and deforestation in Mexico clearly is a big problem. Moreover, he said, "milkweed is considered a noxious weed, and farmers do their utmost to get rid of it."
"It all has to be put in the proper perspective," said Rich Lotstein, a spokesman for Novartis in Research Triangle Park, N.C., which made the corn used in the study and has financed ecological studies. "Please keep in mind that monarchs are probably impacted by cars in the Midwest, too."
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Last Updated on 5/22/99
By Karen Lutz