Subsequent research was unable to reproduce the Tulane findings and in June 1997 the researchers acted responsibly by formally withdrawing their paper, admitting that they too had been unable to replicate their initial results. Those conducting the GM butterfly research were equally responsible. The team leader, John Losey from Cornell University, explicitly warned that it would be inappropriate to draw any conclusions about the risk to monarch populations in the field based solely upon these initial laboratory results. This has not stopped many 'activists' from Greenpeace to the Australian Consumers' Association from doing precisely that. Losey's caveat stemmed not just from the lack of replication of the findings in other studies, but from aspects of the experimental design which meant that the observed toxic effects had little bearing on environmental risk.
Larger larvae are much less susceptible than small.
These are all factors which mean that, even if the toxicity results hold up, there might be a negligible risk to the butterflies. And this risk must be balanced against the benefits of the GM maize, which produces a natural pesticide. These benefits are not only economic, but environmental. Non-GM maize crops are typically sprayed with insecticides eight to ten times, and this is likely to have a more significant impact upon monarch larvae and other insect species. Besides the pollen, the pesticide in GM maize is at least targeted at pests which attack the crop.