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Researchers find bio-engineered corn harms butterflies

monarch butterfly

May 20, 1999
Web posted at: 3:04 p.m. EDT (1904 GMT)

ITHACA, New York (CNN) -- In what may be a rare setback for the booming business of bio-engineered crops, Cornell University researchers reported Wednesday that an increasingly popular strain of corn can be lethal to caterpillars that grow up to be monarch butterflies.

Publishing in the journal Nature, Cornell entomologist John Losey and his research team said "Bt" Corn -- a strain in which genes from a bacteria are spliced into the corn genes -- can kill monarch caterpillars.

The bacterium genes -- from an organism called Bacillum thuringiensis (Bt) -- have proven spectacularly effective in killing off European Corn Borers, moths that eat crops costing corn growers millions of dollars yearly in losses.

Bt corn and other bio-engineered crops also have helped farmers reduce the need for pesticides and other fertilizers while increasing crop yields.

But the Cornell lab research shows that pollen from the Bt corn can be lethal to the caterpillars, which become the graceful, familiar orange-and-black monarch butterflies.


The monarchs feed on milkweed plants, which thrive in "edge habitats" -- the areas where forested land and farm fields meet. Cornell's laboratory research suggests that wind-blown pollen from the Bt corn could disrupt the monarch caterpillar's feeding -- often killing them before they metamorphose from caterpillars to butterflies.

"Monarchs are considered to be a flagship species for conservation," said Cornell entomologist Linda Rayor, an associate on the study. "This is a warning bell."

The Cornell team said the risks to monarchs could be heightened because the butterflies migrate northward through the U.S. Corn Belt from their winter homes in Mexico during the spring months, when corn pollen is thickest.

A spokeswoman for Monsanto, which produces and distributes the Bt seed, said the company welcomes more research. But Lisa Watson of Monsanto cautioned that the Cornell study was conducted under laboratory conditions and may not accurately reflect Bt's impact in farm fields.

She said the company has not yet conducted its own research on Bt's impact on monarch butterflies, but they have found no impact on several other insect species in previous tests.


Monsanto has received U.S. Department of Agriculture approval for commercial sale of Bt strains of corn, potatoes and cotton. More than a dozen other Bt crops are in the field-testing stage.

Some scientists have criticized genetic engineering of food crops on both scientific and ethical grounds for many years, but the Cornell study represents some of the first evidence of possible problems associated with genetically engineered food crops.

Other researchers point to bio-engineering as a potentially vital solution to the food production challenges posed by a growing world population. Indeed, Bt corn and other engineered crops have generally drawn rave reviews from farmers and agronomists for increasing crop yields and reducing the need for pesticides and fertilizers.

The Cornell researchers stressed that consumption of Bt corn poses no threat to humans, nor is there any evidence that Bt corn causes harm to bees, ladybugs or other beneficial insects.

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Cornell University
Crop Science: Transgenic Maize
NC Cooperative: The Status of Transgenic BT Sweet Corn
U.S. Department of Agriculture
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