Study finds GM maize pollen can harm insects

Genetically engineered crops may destroy useful insects through the release of modified crop pollen, according to new research published today.

Modified plants were assumed to have very little impact on non-harmful insects, but researchers from Cornell University in upstate New York have found that pollen from modified maize can poison monarch butterfly larvae.

Engineered maize which carries a gene from the bacteria Bacillus thuringiensis (Bt) produces a toxin harmful to insects that eat the plant.

The pollen also carries the toxin however and can be blown at least 60 metres on wind, settling on nearby plants to be eaten by the larvae, the researchers write in the journal Nature.

Monarch larvae feed on milkweed leaves, a plant that frequently grows in and around the edges of maize fields in the US and Canada.

The researchers gave the larvae plain milkweed leaves, leaves dusted with ordinary maize pollen and leaves that carried pollen from Bt maize plants.

The results were startling. The Bt pollen killed off almost half of the larvae that ate it and the survivors ate less and grew more slowly.

There was no effect on larvae that ate non-modified maize pollen or the plain leaves, the researchers said.

There was no surprise that the modified pollen damaged the larvae because the Bt toxin is known to be dangerous to insects. The researchers were able to show in a dramatic fashion, however, how a genetically modified crop could have an unintentional but devastating impact on an insect bystander.

"These results have potentially profound implications for the conservation of monarch butterflies," said the three researchers, Dr John E. Losey, Dr Linda S. Rayor and Dr Maureen E. Carter. Monarch larvae live exclusively on milkweed leaves and tend to feed during the weeks when the maize plants are shedding pollen.

The planting of Bt maize in the US is projected to rise sharply, the authors noted. "It is imperative that we gather the data necessary to evaluate the risks associated with this new agro-technology and to compare these risks with those posed by pesticides and other pest-control tactics."

These results are published in the week that the British Medical Association called for an open-ended moratorium on the commercial planting of GM crops and a House of Commons committee called for more research into the environmental effects of planting modified varieties.

While the BMA report took a dim view of the technology and emphasised the possibility of unexpected environmental impacts, the Science and Technology Select Committee was generally supportive of the genetic technologies. The report, released yesterday, criticised the media for raising "scare stories" and urged the UK government to take full commercial advantage of what these technologies offered.