GENTECH archive



BBC Wednesday, May 19, 1999 Published at 19:00 GMT 20:00 UK


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. 

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.


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

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

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

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

"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

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.

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