In 1999 John Losey and colleagues from Cornell University published a paper in Nature showing that, at least in the laboratory, the larvae of monarch butterflies could be poisoned by maize pollen containing a natural insecticide, called cry, that had been genetically engineered into the plants. Many anti-GM environmentalists (although not Dr Losey) used these findings to claim that GM maize would harm Monarch butterflies in the wild.

Now a series of papers in The Proceedings of the National Academy of Science 14 Sept 2001, including two by Dr Losey himself, have shown that this is very unlikely. It turns out that even in the lab only one commercial maize strain, accounting for two percent of maize crops, contains the insecticide in a form that damages larvae, and that strain is being withdrawn. Even if the pollen were toxic, it would be unlikely to cause harm in the field because most of it accumulates on parts of the plants away from where the caterpillars feed. Finally, field trials show that traditional insecticides are more destructive of monarch butterflies than the GM variety, which has replaced them.