By Bart B. Van Bockstaele

Genetically modified cotton in China seems to be of tremendous benefit, not
only because the modified plants can defend themselves against the reviled
bollworm, but also because those plants seem to protect their unmodified
brethren.
When asked what they think about genetic modification, members of the
general public usually either don't care, or vehemently oppose it. In some
ways, this is a healthy reaction, clearly resulting from our evolution. It
is a survival strategy. What one doesn't know, may kill one. Scientists, who
have learned that our evolved brain doesn't always see things realistically,
have more nuanced opinions.

Genetically modified crops can have tremendous advantages. A normal plant
can be modified to become resistant against diseases and other pests,
thereby avoiding the need for pesticides. But the advantages don't
necessarily stop there.

Nature reports that a ten-year study in China has now shown that cotton
plants that are genetically modified to produce a toxin against the cotton
bollworm, Helicoverpa armigera, one of Asia's most devastating insects. It
attacks corn, cotton, peanuts, soya beans, vegetables and wheat. Several
bollworm outbreaks in China in the early 1990s were barely contained through
heavy pesticide use that killed thousands of people every year.

Bollworm is sensitive to a toxin made by the bacterium Bacillus
thuringiensis (Bt). In 1997, China has allowed to cultivate on a commercial
scale cotton plants that are modified to produce this toxin. 4 million
hectares are now planted with this Bt cotton. Scientists have monitored the
bollworm populations in part of Northern China since 1992. They study an
area with 3 million hectares of Bt cotton and 22 million hectares of various
others crops that the bollworm can infect.

The interesting part is that since Bt cotton was introduced, bollworm has
not just declined in Bt cotton, but also in other crops. This was most
apparent in the period from 2002 to 2006. Through the application of
statistical analyses, the scientists have found that there is a better
correlation between the reduction of bollworm and the amount of land planted
with Bt cotton than with weather patterns, such as temperature or rainfall.

In order to find out why this happens, the researchers have planted Bt
cotton together with normal cotton in a test field. They have done that for
10 years, from 1998 to 2007. No pesticides were used. Both crops contained
similar amounts of bollworm eggs. However, the Bt cotton contained fewer
larvae than the non-modified cotton.

There are normally four generations of bollworm per year in northern China.
The first generation tends to grow on wheat and lay its eggs on cotton. The
scientists think that the overall reduction is due to the fact that the eggs
laid on Bt cotton are being killed off which leads to a smaller second
generation.

"It's a very nice study with an impressive sample size," says David Andow,
an entomologist at the University of Minnesota in St Paul. However, he also
warns that it "does not rule out other factors that might affect the insect
populations".

Pesticide use was reduced after the introduction of Bt cotton, but secondary
pests, such as mirids, have increased. That has led to more spraying since
2001. Andow thinks that this may have contributed to the further decline in
bollworm populations from 2002 to 2006.

In China, cotton is often grown as a monoculture. This increases the risk
that the bollworm would become resistant to the toxin of Bacillus
thuringiensis. Although there has not been any appropriate resistance
management, not much resistance has been found thus far. Scientists suspect
that this may be because the other crops are usually grown on small farms
next to the resistant cotton fields. This would offer a protection against
resistance, even though they do benefit from the overall bollworm reduction.

The researchers think their study shows that genetic modification can be a
powerful way to control pests and that other Bt crops, such as Bt rice, may
hold great promise for the future of agriculture in China.

Some entomologists, such as Kong Luen Heong, an entomologist at the
International Rice Research Institute in Los Banos, Philippines, caution
that strategies like this one can not be used everywhere. "If the insect
feeds on a single host, as many rice pests do, one would not expect such
accidents," he says.

Several Bt rice varieties are waiting approval for commercial use by the
Chinese ministry of agriculture. If they were grown on a large scale without
proper resistance management, there could be devastating consequences, says
Heong.
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