The biotech debate: The monarch butterfly

Monarch larvae feed on milkweed in corn fields

By BBC News Online's Helen Briggs

Entomologist John Losey could hardly have imagined the furore that would ensue when he happened to wonder, during a field trip one summer, whether dustings of pollen on milkweed growing in a Bt-cornfield might harm the monarch butterfly.

This curiosity, the lifeblood of any scientist, sparked one of the biggest environmental debates of the decade - could butterflies like the monarch be at risk from genetically-modified (GM) crops?

It doesn't seem like there's an immediate catastrophic risk to monarchs

Dr John Losey, entomologist

As with any big scientific question, arriving at an acceptable conclusion is an uphill slog.

Nearly two years after Losey and co-researchers at Cornell University, New York, showed that monarch caterpillars died in the laboratory after eating pollen from genetically engineered corn, experts are still divided over whether monarchs are at risk in the wild.

Meanwhile the monarch, the state symbol of Minnesota, has become an emblem of the struggle between environmentalists and industry over the changing face of farming.

Hazard warning

The first alarm bells were sounded in spring 1999, when a letter by the Cornell team appeared in the leading scientific journal Nature. Their laboratory study showed that consumption of large amounts of Bt-pollen is hazardous to monarch larvae.

Further evidence in support of these findings came in August last year. Researchers at Iowa State University said they had found monarch caterpillars were seven times more likely to die when they ate milkweed plants dusted with pollen from Bt-corn rather than conventional corn.

But demonstrating what happens in the real world is more contentious. In theory, for butterflies to be at risk, they would have to be present in the cornfields at the time that pollen was shed. They would also need to be exposed to enough pollen for it to be harmful. In an attempt to resolve the question of risk, independent and industry-sponsored scientists headed to the field to study the butterfly in its natural habitat.

Monarchs migrate for thousands of miles

The monarch butterfly leads a fragile existence. In the winter, it hibernates along the coast of southern California or in the fir forests of central Mexico. Come the spring, it heads northwards in the most spectacular migration of any insect. By the time the monarch reaches its breeding ground, the vast American cornbelt, it may have flown as far as 4,800 kilometres (3,000 miles).

The monarch faces many threats to its survival. A snowstorm in 1995 killed 5 to 7 million monarchs during their incredible journey north. Prey to predators like ladybugs and lacewings, less than 5% of the caterpillars survive to adulthood, even on standard corn.

But human activities pose perhaps the biggest threat. The mountain forests of central Mexico are vulnerable to logging and the coast of southern California to development. At the monarch's breeding grounds, pesticides destroy milkweeds, the sole food source for the caterpillars.

The kinds of things that are blown up out of proportion are that monarchs are going to be gravely endangered

Robin Yeaton Woo, Ceres Forum

Any added risk from Bt-corn, say environmentalists, could tip the delicate balance too far. But that stance has been attacked by some scientists as over-hyped.

"The kinds of things that are blown up out of proportion are that monarchs are going to be gravely endangered," says Dr Robin Yeaton Woo of the Ceres Forum, Center for Food and Nutrition Policy, Washington DC.

"Frankly as an insect developmental biologist, that's a real half story, there's no way when you look at broad-spectrum pesticides that monarchs are even in as great a danger with Bt-corn as they are when airplanes fly over dusting whole crops with poison."

Lobby groups

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

Industry soon hit back, seizing on data, announced at a symposium organised by a consortium of biotech and pesticide companies, which suggested that most Bt- corn pollen was shed within a cornfield rather than outside of it. Any risk to the butterflies would be small, said an industry spokesman, if, as was then thought, monarchs seldom ventured into cornfields.

But last summer, researchers led by Dr Karen Oberhauser of the University of Minnesota discovered that cornfields act as a haven to monarchs. They found large numbers of monarch caterpillars between the rows of corn. Debate now centres on whether pollen levels present at the time the monarchs breed is enough to do the larvae any harm. Preliminary results suggest not.

GM crops have been the subject of protests in the UK

"A lot of work has been done on how much pollen actually gets on milkweed leaves in a cornfield," says Mark Buckingham, a spokesman at the biotechnology company Monsanto's headquarters in St Louis, Missouri.

"This is work in progress but it looks like in the field, even for the single day in the season when pollen shed is at its greatest, which is obviously only a very small fraction of the pollen of the monarch breeding season, does pollen shed get up to one-third of the level necessary to damage monarch butterflies."

But not everyone is convinced. "We don't have a clear picture of the overall risk yet, however we're a lot closer," says Dr David Andow, an entomologist at the University of Minnesota who has been monitoring the developments.

And there are further complications. It seems that monarch caterpillars may be particularly vulnerable to the toxic pollen at a stage of development when they start feeding on the outside, rather than the underside, of the milkweed leaf, where pollen is more likely to scatter.

We don't have a clear picture of the overall risk yet however we're a lot closer

David Andow, University of Minnesota

In an attempt to calm public anxiety, the US Environmental Protection Agency (EPA) called for all registrants of Bt-corn plant pesticides to submit data on the effects of Bt-corn pollen on non-target species, particularly the monarch butterfly, by March 2001.

Although the EPA said in a draft report on GM crops last September that the risk to the butterflies ranged from low to very little, insiders acknowledge that "the jury is still out" on the issue.

And Dr John Losey says that resolving the risk question will take a substantial commitment of resources, from industry or government agencies.

"It doesn't seem like there's an immediate catastrophic risk to monarchs," says Dr John Losey. But he warns that any long-term risk to the butterflies may be more subtle and harder to measure.

Dr Losey's team originally estimated that it would cost between $2m and $3m to solve the monarch question. Two years on, there is still a long way to go. It is a measure, perhaps, of how difficult it is to resolve some of the big environmental questions posed by biotech crops and the financial resources needed to do so.