Members of a scientific advisory panel convened to advise the U.S. Environmental Protection Agency on the registration of bioengineered crops took the agency to task Oct. 19 for concluding in a preliminary risk assessment that such crops pose minimal risk to monarch butterflies. Furthermore, scientists on the panel said that preliminary data from a series of ongoing studies suggest that monarch butterflies could be impacted by these so-called Bt corn crops, which appear to constitute a more significant habitat for the butterflies than previously known.

Bt crops have been genetically altered to produce the same toxin generated by the Bacillus thuringiensis bacterium, which is lethal to certain pests such as the European corn borer.

Initial laboratory studies suggested that the Bt toxin present in corn pollen might also kill the larvae of monarch butterflies, because they breed on milkweed plants that are often found in or near cornfields. These initial studies have proven to be controversial because they were not conducted in the field and have received extensive media attention.

Not Enough Data

"I am concerned that EPA is attempting to reach conclusions in the almost complete absence of field data," said Chip Taylor, a professor in the department of entomology at the University of Kansas. "In the absence of the data of the susceptibility of monarch larvae [to Bt corn pollen], it is totally premature to accept the point of view or the interpretation that Bt corn pollen is not going to have an effect on monarch butterfly populations." More field studies are needed to explore the possible impact of these genetically altered crops on the butterflies before any conclusions should be reached, the scientists agreed.

Comment Sought

EPA had asked the panel to comment on its analysis of the potential impacts of three kinds of Bt toxins on monarch butterflies. "The agency concludes that the published preliminary monarch toxicity information is not sufficient to cause undue concern of widespread risks to monarch butterflies at this time," the agency analysis concluded, although it added that "EPA will continue to closely monitor the results from the monarch butterfly research as a part of its regulatory oversight of Bt products."

Scientists on the panel acknowledged that the agency had based its conclusions on data available at the time, but the paucity of that data should instead have led the agency to reach no conclusions on the possible effects of Bt corn on monarch butterflies.

"While I realize that we had to work with the available data, I feel that this report drew conclusions that should have just said: 'We don't know,' " Karen Oberhauser, a professor in the department of ecology, evolution, and behavior at the University of Minnesota, said.

New Studies

Oberhauser's new and currently unpublished research into monarch butterflies in cornfields appears to contradict a number of the conclusions reached in the EPA report. She noted that a number of reports claim that monarch larvae are not as susceptible to the Bt toxin in their later stages of the development, when no such studies actually exist. Recent studies in which she participated found that monarch larvae exposed to Bt pollen actually suffered deleterious effects in later stages, she said.

"I think the conclusions of no sublethal effect [are] incorrect, and also the conclusion that only neonates are susceptible to the pollen is incorrect," she said.

She also noted that her research suggests that cornfields actually provide excellent habitat for monarch butterflies. "What our results suggest [are] that cornfields are actually excellent monarch butterfly habitats even though milkweed densities may be lower than they are in other habitats," Oberhauser said.

This also suggests that another conclusion in the report, that "there is no pollen shed and monarch breeding overlap in most of the Corn Belt," is inaccurate, she noted.

"We found in Minnesota and Ontario that peak monarch abundance and final generation before migration, the last generation of the summer, overlapped almost perfectly with pollen shed," she continued. "We found that pollen was shed before peak monarch abundance in Iowa and Maryland, but there was still significant overlap between pollen shed and monarch presence in the environment."

An easy way to make all of these concerns moot would be by engineering the Bt crops so that they do not express the toxin in their pollen, she added.

Significant Habitat

Other scientists weighed in with observations that cornfields appear to provide significant habitat for monarch butterflies. Taylor of the University of Kansas said he found that about 90 percent of the monarch butterfly habitat is agricultural and between 10 percent and 19 percent of the total breeding habitat is corn.

Because of the extent of the monarch population that could be found in cornfields, between 5 percent and 9 percent of the total breeding population could be at risk if Bt corn becomes widely used, he added.

Although examples can be found of species that breed in disproportionately small areas of the available habitat, Taylor conceded, the sheer number of monarch butterflies--about 200 million to 400 million--could not come from the 10 percent of its habitat that is considered to be nonagricultural land.

Cautions

Other scientists, however, warned that some of the existing studies suggesting possible harm to the butterflies are sorely lacking in their methodology and point out the dire need for additional field studies. Mark Sears, a professor in the Department of Environmental Biology at the University of Guelph in Canada, said he was particularly skeptical of the methodology used in an Iowa State University study showing that Bt pollen could be lethal to the monarch butterfly.

Based on such a small sample and using questionable techniques, "we're going to base a decision on whether to register a corn product in the U.S. of A?" he asked. "I don't think so!"

Meanwhile, Richard Hellmich of Iowa State University warned against treating all strains of Bt corn alike given that they are all different.

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