Magazine article Science News

Bt-Corn Pollen Can Kill Monarchs

Magazine article Science News

Bt-Corn Pollen Can Kill Monarchs

Article excerpt

Eating pollen from corn plants genetically engineered to make their own pesticide can kill larvae of monarch butterflies, according to a Cornell University study.

The results raise doubts about a supposed smart bomb in the pesticide arsenal, the Bt toxin. Biotech companies sell corn carrying the toxin gene, designed to protect the crop from moth caterpillars with minimal collateral damage to bees and other beneficial insects.

In a laboratory test, about half of the monarch caterpillars died after 4 days of munching on leaves dusted with Bt-corn pollen, report Cornell's John E. Losey and his colleagues. All the caterpillars that ate regular corn pollen survived, the researchers note in the May 20 NATURE.

"We don't know how big the risk is," Losey cautions. More tests need to answer such questions as how much pollen coats leaves in the real world and whether wild caterpillars avoid coated leaves, he says.

The Bt toxin, discovered in the bacterium Bacillus thuringiensis, kills its victims by perforating their guts. In 1996, Novartis Seeds of Golden Valley, Minn., introduced corn souped up with the Bt gene to fight corn borers. By 1998, up to 16 million of the 80 million acres of corn harvested in the United States carried some form of the gene, according to Monsanto Co., a St. Louis firm that licenses the technology behind Bt corn.

Earlier tests did not explore Bt effects on monarchs, says Cornell's Linda S. Rayor, a coauthor of the new study. The caterpillars eat leaves only from milkweed, which thrives along roadsides and field edges. Rayor lives near a cornfield and can testify that corn, which is wind-pollinated, sheds pollen beyond field borders.

Other butterfly caterpillars feed near fields, too. "I think there's a really good chance the pollen affects less charismatic species," she says.

Losey points out that previous work had already raised questions about Bt's safety. …

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