When Cornell University researchers published in Nature last May that pollen from Bt corn posed a risk to Monarch butterflies, the laboratory study was used as an emotional rallying point for anti-biotech activists. Further research suggests a negligible risk of butterfly toxicity from the genetically modified crop. But despite the overall conclusion of last week's Monarch Butterfly Research Symposium in Rosemont, Ill., that Bt pollen is not a significant risk, the case is not yet airtight.

In a University of Guelph (Ontario) study presented at the symposium, for example, Bt pollen was found primarily within 5 meters of the edge of a Bt corn field. However, the dense pollen found within that region was found to be toxic to Monarch larvae, providing grist for the defenders of the Cornell research