GM pollen 'can kill butterflies'

The monarch caterpillars feed on the milkweed plant

By Environment Correspondent Alex Kirby

Pollen from one of the most successful genetically modified (GM) crops in the US can kill the larvae of monarch butterflies, scientists say.

Their study, published in the journal Nature, shows how the new GM technology might have unwanted consequences for biodiversity.

Nearly half of the GM pollen-fed caterpillars died

The Cornell University researchers say their results "have potentially profound implications for the conservation of monarch butterflies" and believe more research on the environmental risks of biotechnology in agriculture is essential.

Their experiments looked at Bt-corn which has been modified to incorporate a gene from the bacterium Bacillus thuringiensis (Bt).

This makes the plant tissue toxic to the European corn borer, a significant pest that hides in the stalks of the plant, making it difficult to control with chemical sprays.

Although the Bt-corn plant itself is harmless to humans and other creatures such as ladybirds and bees, the researchers found pollen from the GM crop could have a lethal effect on the larvae of monarch butterflies if it lands on the plant on which they feed - milkweed.

This is commonly found around cornfields and is the exclusive food of monarch caterpillars.

Dead caterpillars

In the laboratory, Monarch caterpillars fed on milkweed leaves dusted with Bt-corn pollen ate less, grew more slowly and suffered a higher mortality rate than those fed on leaves with normal pollen, or with no pollen at all.

Nearly half of the GM pollen-fed caterpillars died, while all the rest survived the study.

The crop is harmless to non-target insects

The scientists say the GM pollen enters the caterpillar's gut, where it binds to specific sites. The gut wall then changes from a protective layer to an open sieve, allowing pathogens normally contained in the gut and then excreted to enter the insect's body.

Last year more than seven million acres of Bt-corn were planted in the US. Before its development, borers used to cause an average annual loss of $1.2bn.

The technology offers significant potential for reducing pesticide use and increasing yields. Any negative effects therefore need to be balanced against these benefits, says Assistant Professor of Entomology John Losey, the lead researcher on the Nature paper.

"We need to assess the risks from this Bt pollen and then balance those with the proven benefits and then decide, objectively, what is better for the environment," he told the BBC.

"We want to look at the plants that are common around cornfields and the different butterflies whose caterpillars would feed on those plants. By putting those together, we can start to get a sense of what the total impact of this pollen might be."

Novartis Seeds were the first biotechnology company to sell Bt-corn and their products are now grown commercially in the US, Canada, Argentina and Spain.

"This study does not give any basis for a change in our marketing of Bt-corn," their spokesperson Sheena Bethell told BBC News Online.

"Bt-corn has been extensively studied and we already have several years of growing experience in the US - one lab experiment does not change that. We follow and exceed all the requirements made by regulatory authorities which are very rigorous.

"Even if there are unwanted effects on the Monarch butterfly, you still have to put that into the context of comparison with other forms of control."

However, English Nature, the UK Government's wildlife advisor is using the publication of the report to renew its call for a delay in the commercial planting of insect-resistant crops in Britain.

"This new research confirms the views put forward by English Nature last year that there are serious concerns about the commercial introduction of GM crops before research has been done on their potential effects on biodiversity," it says.