Claim: The continuing discussion concerning the endangerment to the monarch butterfly posed by Bt-corn has reached a climax in the conjecture that a large number of butterfly species in Europe are also under threat from the large-scale cultivation of Bt-crops. In a Greenpeace press release of June 24, 1999 it was stated that: "Greenpeace has found out that 140 butterfly species in Europe are at risk. ... The release of genetically engineered corn could trigger a mass extinction of butterflies."

The facts: Cry1Ab, the toxin produced in Bt-corn is, even in comparison to modern chemical insecticides, extraordinarily selective. It has an effect exclusively on species within the order of butterflies to which the corn borer and the monarch butterfly belong. In fact a large number of butterfly species (perhaps as many as 250) would probably react with similar sensitivity to conditions monarch caterpillars were subjected to in the feeding studies of Dr. Losey. From this context, however, it is short-sighted to prophesy an imminent ecological catastrophe for the "colourful world of butterflies" since projecting strictly defined laboratory findings onto the open field is only possible under very limited conditions.

The decisive question is not whether or not the toxin produced in Bt-corn pollen is potentially poisonous for a particular species of butterfly but whether that species comes into contact with Bt-toxin during its life cycle. The experimental conditions chosen by Dr Losey describe the rather more fictional scenario in which all monarch females lay their eggs exclusively on host plants in the middle of a maize field in full bloom and which are covered with a thick layer of Bt-pollen.
That may be one facet of reality but certainly not the dominant one. A comparison makes this clearer: If one wanted to carry out a comparable study in order to judge the effects of conventional means of plant protection on monarch caterpillars, one would have to mistreat the host plant and the caterpillars living on it in a shower of insecticides. How many caterpillars would survive?

Some of the "facts" in the Greenpeace press release of June 15, 1999 may lead to misunderstandings and deserve an explanation: For example, it was then claimed that the Losey study had been confirmed by investigations at Iowa State University.

The truth is merely that a student had presented a poster on a similar experiment at a local entomologists' meeting at the end of March. The abstract can be found on the internet but this does not allow an interpretation as the methodology is not elucidated and a corresponding article has not been published to date. In another passage of the press release it is stated that, "corn pollen can be carried as far as 200 metres by wind." That may be possible, theoretically, but that does not guarantee it happening as a rule. Maize pollen is quite dense and does not normally get much farther than 5 metres. Pollen drift can be considerably restricted by planting buffer rows of conventional maize so that no appreciable amount of Bt-pollen reaches surrounding areas.

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