Despite some uncertainties, the monarch butterfly faces little threat from genetically modified (GM) strains of corn, according to new research presented at a symposium sponsored by the biotechnology industry. Although agricultural scientists admit that more research into the butterfly's real-life interaction with corn needs to be done, they agree that earlier characterizations of peril to the butterfly were likely overstated.

The findings were presented by the Agricultural Biotechnology Stewardship Working Group—a consortium of agribusiness firms—at a one-day symposium and press conference held near Chicago on November 2. The symposium and studies were organized in response to a report last May by Cornell University researchers who found that high proportions of monarch larvae died after being force-fed milkweed plants that were covered by pollen from GM corn (Nature, 399, 214, 1999). Plant scientists and representatives of life science companies criticized the work as premature and incomplete (Nat. Biotechnol. 17, 627, 1999).

"The worst-case image of this toxic cloud of pollen saturating the Corn Belt and wiping out the Lepidoptera species including monarchs is clearly not the case," says Stuart Weiss, a Stanford University researcher. "The pollen has a limited shadow (distribution) and the toxicity of the pollen is not as toxic as thought."

The GM corn contains genes for a protein from a common soil bacterium, Bacillus thuringiensis (Bt), and is prevalent in more than 30% of the corn grown in the United States. Milkweed plants, a favorite food of butterfly larvae, grow within and around the edges of cornfields.

Several lines of evidence presented at the conference suggest GM corn presents little threat to monarch larvae. Galen Dively of the University of Maryland noted that pollen concentrations drop off rapidly several meters from the cornfield, suggesting that milkweed farther away will be relatively pollen free. Other data presented showed that various strains of Bt corn had differing rates of toxicity to monarchs, that harmful pollen is often washed off or blown off milkweed leaves, and that 95% of corn pollination in Nebraska was complete before the first monarch eggs hatched. (Adult butterflies feed on plant nectar and are not affected by toxin-containing pollen.)

In the earlier Nature paper, Cornell entomologist John Losey used a low toxic strain of pollen. He presented new research in Chicago showing that adult monarchs avoided laying eggs on milkweed leaves near corn plants and those covered with pollen.

However, Chip Taylor, an ecologist at the University of Kansas, says scientists still don't know the real-world interaction between butterfly larvae, milkweed, and corn pollen. "What we need to know is how much monarchs are using milkweed at the edge of corn plants and their rates of morbidity and mortality," he says. "We still don't have that."

Of the 20 studies presented at the conference, 60% were funded by the industry group, which included Monsanto (St Louis, MO), Novartis AG (Basel, Switzerland), and Pioneer Hi-Bred (Des Moines, IA), which is owned by DuPont. The remainder were funded by individual institutions or the US Department of Agriculture (Washington, DC).

"We all agree that we have some of the data we need," says Losey, "But the question of risk assessment still hasn't been answered."

Some critics argue that the studies reported at the meeting were too short and were not put through the peer-review process before being presented to the public. "There are a lot of conclusions being made on very preliminary data," says Rebecca Goldburg, a senior scientist at the US Environmental Defense Fund, "It seems a little premature."