Scientists discuss GM threat to butterflies

More research is clearly called for

There seems little consensus in the scientific community as to the precise impact genetically modified (GM) corn (maize) will have on monarch butterflies.

There has been particular concern about the fate of the familiar insect after Cornell University, US, researchers showed how pollen from corn modified to produce its own insecticide could kill monarch larvae if it landed on milkweed plants, the exclusive food of monarch caterpillars.

Since the Cornell study was published in the science journal Nature last May, environmental lobby groups opposed to GM crops have used the monarch butterfly as a focus for their attacks on the biotech industry.

But at a symposium in Chicago which brought together many scientists working in this area, there appeared to be conflicting evidence as to the true state of play.

The meeting was organised by a consortium of biotechnology and pesticide companies in the US, the Agricultural Biotechnology Stewardship Working Group. It had commissioned a number of studies in response to the Cornell work, some of which reported preliminary findings at the symposium.

In one study conducted at the University of Maryland, it was found that corn plants did not release their pollen in Maryland when Monarch caterpillars were feeding on milkweeds.

But Pennsylvania State University, which used computer models to look for an overlap in larval feeding and pollination in six other corn-producing states, found a much more mixed picture: in some areas the overlap was close to 100%, in others there was hardly any overlap at all.

Pollen travel

There were some data presented which suggested that toxicity depended on the variety of GM corn used. Other data suggested the pollen from GM corn did not travel as far as many thought.

GM pollen was shown to be harmful to Monarch larvae

University of Guelph, Ontario, research found that 90% of pollen grains travelled less than five metres from the field, and virtually all landed within 10 metres.

"The worst-case scenario is not true," said Dr Stuart Weiss, a researcher at Stanford University. "There's not a toxic pollen cloud wiping out monarchs and all species."

But nearly all the material presented at the symposium has yet to be peer reviewed or published, which means this debate will run for some time.

GM corn has become very popular with American farmers. It 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.

Assistant Professor of Entomology John Losey, and colleagues, at Cornell University, found that 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 in the now famous Cornell study died, while all the rest survived.