Published online 20 May 1999 | Nature | doi:10.1038/news990520-1

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GM crop gatecrashes butterfly ball

Genetically modified corn could kill caterpillars far from the cornfield, according to a report in the 20 May issue of Nature. John E. Losey and colleagues of Cornell University, Ithaca, New York and colleagues show that genetically modified corn pollen dusted onto the leaves of milkweed (Asclepias sp.) has the potential to kill caterpillars of the monarch butterfly (Danaus plexippus).

Laboratory experiments showed that almost half (44%) the caterpillars fed on leaves dusted with GM pollen died, whereas caterpillars fed with leaves coated with normal pollen, or clean milkweed leaves, were unharmed. The GM-pollen-fed caterpillars also ate (and grew) much less well than the other caterpillars, irrespective of their increased mortality.

In the wild, monarch caterpillars feed exclusively on milkweed, which is commonly found around cornfields in the monarch's North American range, which overlaps the so-called 'corn belt' of the midwestern United States. Corn pollen can be transported at least 60 metres by the wind, so it is possible that pollen from GM corn could find its way onto milkweed leaves. Furthermore, corn sheds its pollen for 8-10 days between late June and mid-August, which is when monarch larvae are feeding.

Importantly, the caterpillars were not killed by genetic material that had escaped into the environment, but by the product of a gene introduced into the corn. The gene, from the bacterium Bacillus thuringiensis (or Bt for short), stays in the corn - but it contains instructions for a protein which is poisonous to insect pests. The introduced gene makes this toxin in the corn as it would in its bacterial home. Insects eating corn with the Bt gene would ingest the toxin and die. This - rather than the actual transfer of genetic material - is what killed the caterpillars in the experiments, the researchers believe.

"With the amount of Bt-corn planted in the United States projected to increase markedly over the next few years, it is imperative that we gather the data necessary to evaluate the risks associated with this new agrotechnology", the researchers say.