Genetically engineered corn plants appear to pose only a modest and perhaps insignificant threat to monarch butterflies, according to several new studies described yesterday at a scientific symposium.
The mixed but mostly reassuring findings come five months after Cornell University researchers triggered widespread concern by suggesting that pollen from gene-altered corn plants may be killing the popular insects.
That study was criticized as sloppy by biotechnology industry scientists and others. But the brilliant orange, black and white butterfly became an instant mascot for activists concerned about the environmental impact of high-tech crops, and prompted a U.S. public relations crisis for an industry that already faced widespread vilification in Europe, where gene-altered crops and foods have been widely rejected.
In the aftermath of the Cornell report, a consortium of biotechnology and pesticide companies quickly funded several studies to quantify the risk posed by corn containing a bacterial gene called Bt. Yesterday's meeting was sponsored in Chicago by that consortium, the Agricultural Biotechnology Stewardship Working Group, and included early results from academic researchers and others, many of whom were funded by the industry group.
"One thing that came out pretty clearly today is that the worst-case image that may have gotten out there of a toxic cloud of pollen engulfing the Corn Belt and wiping out all the [butterflies] is clearly not the case," said Stuart Weiss, a Stanford University expert in ecological modeling, who presented data at the meeting.
But there is still a lot to learn about the complex ecological interactions in question, Weiss and others said. And some activists criticized federal regulators for allowing the crops to be so widely planted while questions remained.
At issue are several varieties of gene-altered corn, planted in the United States since 1996, which now account for about a third of all corn acreage in this country. The plants produce a toxin deadly to corn-boring caterpillars, which cause about $1 billion in crop damage each year.
In May, John E. Losey and colleagues at Cornell reported that monarch caterpillars died after eating milkweed leaves dusted with pollen from Bt corn plants. That raised the specter of windblown pollen killing beneficial insects that themselves eat insect pests, as well as popular creatures like the monarch, whose sole source of food, milkweed, often grows close to corn fields.
In one study described yesterday, Galen Dively of the University of Maryland found that corn plants in Maryland do not release their pollen when monarch caterpillars are feeding on milkweeds.
Pennsylvania State University entomologist Dennis Calvin used computer models to look for such overlap in six other corn-producing states, with mixed results. In some areas the overlap of pollen and feeding was close to 100 percent, he said, while in others there was no overlap. Overall, he concluded, "the impact is uncertain."
Others tracked how far corn pollen blows beyond corn fields. Mark Sears of the University of Guelph in Ontario found that 90 percent of pollen grains travel less than five yards from the field, and virtually all land within 10 yards. Sears also found that it takes at least 500 grains of pollen on a square centimeter of milkweed leaf to sicken monarch caterpillars--a concentration he found was barely attained on nearby milkweed leaves after three days of accumulation during pollination season.
Based on those findings, he said, "I'm assuming the risk of the hazard to monarch larvae is very minimal."
Iowa State University scientist John Pleasants found significant differences in pollen concentrations on nearby milkweed plants depending on wind direction, rainfall and other factors. That means that under some conditions, monarchs may indeed be threatened by Bt pollen, he said. But in general, he said, monarchs feeding more than a yard from a corn field are probably "100 percent safe."
Cornell's Losey said his latest experiments suggested that, given a choice, monarchs may avoid pollen-laden milkweed plants near cornfields. But he said he still had concerns about the insects' welfare. "I think it's too early to be reassured, or more alarmed, based on this data," Losey said.
John Foster, a University of Nebraska entomologist, said he believes corn pollen poses an insignificant threat to the monarch, compared with the regular mowing of milkweed-rich meadows and rights-of-way in the United States and habitat destruction in Mexico, where the butterflies reside during the winter.
Asked whether the industry's funding of his research might bias his views, Foster said: "They don't give me enough money to buy my opinions."
CAPTION: A monarch butterfly stops in Virginia during migration in September. Earlier research indicated a threat to the insect.