A second study has found that pollen from genetically engineered corn plants can harm monarch butterflies.
About 20 percent of monarch larvae died after being exposed to pollen from corn genetically engineered to produce a pesticide that had blown onto nearby plants that the monarch caterpillars eat, the study found.
The finding reignites a heated scientific and regulatory debate over whether biotech crops in general, and the engineered corn in particular, pose heightened risks for the environment, and whether federal authorities have appropriately addressed those risks.
"This takes the monarch research a step further," said John Obrycki of Iowa State University, who conducted the new study. "We had lab research showing the effect, and now we have a modified field study that shows an effect as well."
But both the biotech industry and the federal Environmental Protection Agency cautioned against making conclusions based on the study, which looked at the effects of corn modified to produce a pesticide called Bacillus thuringiensis (Bt). Opponents of the corn have been concerned that pollen from the plants containing the pesticide could blow onto nearby plants where the monarch caterpillars feed.
According to Stephen Johnson, deputy assistant administrator for the EPA, tests monitoring the engineered corn in fields have not shown any negative consequences of the Bt-producing corn on monarchs. "There may be a potential hazard, but research shows there is unlikely to be any significant exposure to Bt toxin by the monarchs," Johnson said.
Val Giddings, vice president for food and agriculture of the Biotechnology Industry Organization, also said that the theoretical risk of Bt pollen on monarchs has not been found in the field.
"Dr. Obrycki's research stands in the shadow of more than 20 independent studies by widely recognized scientific experts who have found that Bacillus thuringiensis corn does not pose a significant risk to the monarch butterfly," he said. "This report considers only one small area of this complex topic and the conclusions put forward by the authors stand in stark contrast to those of the broader scientific community's research."
Obrycki agreed that the potential harm from Bt corn remained unclear. To be harmed, monarch larvae would have to appear at the same time that the corn pollen was flowering, and the overlap of the two events was necessarily limited, he said. Growing conditions in different areas and planting times, he continued, would determine where the danger might lie.
Nonetheless, he and co-author Linda Hansen concluded in their paper, published in the journal Oecologia, that "the ecological effects of (genetically engineered crops) need to be evaluated more fully before they are planted over extensive areas."
Bt corn has been planted since 1996, and now accounts for about one-third of all corn planting. The Bt in the corn protects against corn-boring caterpillars, which cause an estimated $1 billion in yearly crop damage. Much of the nation's corn is grown in the Midwest, which is on the migration path of monarchs.
The butterflies feed exclusively on milkweed plants, which commonly grow in or near cornfields. The pollen from the corn can blow onto the milkweed.