A study in northern China indicates that genetically modified cotton,
altered to express the insecticide, Bt, not only reduces pest populations
among those crops, but also reduces pests among other nearby crops that have
not been modified with Bt. These findings could offer promising new ideas
for controlling pests and maximizing crop yields in the future.
The report was published by the journal Science on Friday, 19 September.
Science is the journal of AAAS, the nonprofit science society.

Dr. Kong-Ming Wu from the Chinese Academy of Agricultural Sciences in
Beijing and colleagues analyzed data from 1997 to 2007 about the agriculture
of Bt cotton in six provinces in northern China, covering 38 million
hectares of farmland cultivated by 10 million resource-poor farmers. They
compared that information with data on pest populations in the region,
focusing on the cotton bollworm, a serious pest for Chinese farmers.

The researchers' results show that populations of the cotton bollworm were
dramatically reduced with the introduction of Bt cotton, especially during
the period from 2002 to 2006. They considered the contribution of
temperature and rainfall along with the introduction of the genetically
modified cotton, and confirmed that Bt cotton was responsible for the
long-term suppression of the pests in the cotton and a host of other
un-modified crops after 10 years. Dr. Wu and colleagues suggest that this
may be because cotton is the main host for bollworm eggs, and reducing
larval populations in the cotton consequently reduces the entire population
and protects other crops.

Bt is an insecticide derived from the spores and toxic crystals of the
bacteria Bacillus thuringiensis, and has been sold commercially since 1960.
It is considered non-toxic to humans, animals, fish, plants,
micro-organisms, and most insects. However, it is highly selective and
lethal to caterpillars of moths and butterflies. Bt is currently registered
and marketed for use as an insecticide in more than 50 countries worldwide.
It does not contaminate groundwater because it degrades so rapidly.

The authors say that Bt technology gives China a new tool for pest control,
and that all farmers in a Bt cotton-planting region will experience the
benefits. "In 1992, cotton bollworms caused about a 30 percent loss in the
cotton yield in northern China. Because of the high costs for pest control
then, many farmers refused to plant cotton," said Dr. Wu in an email
interview. "This case study of Bt cotton implies that other Bt crops, such
as Bt rice, may also have great potential for agricultural practices in
China. This success with Bt cotton could push forward the commercial
processes of genetically modified crops in China."

Dr. Jian-Zhou Zhao, a co-author of the report, also highlights the health
benefits of using Bt cotton. "Poisoning from other insecticides, and even
death, was a big problem for cotton farmers in the 1990's," Zhou said. "Most
farmers did not have proper protective clothes while applying insecticides
with small backpack sprayers. This may be another reason that many farmers
refused to plant cotton before Bt was available -- it was too dangerous and
scary."

The use of Bt cotton and other genetically modified crops could provide a
safer and more economical solution to pest control in many small farms
around the world. Dr. Wu and the team of researchers, however, acknowledge
that a major challenge to the success of Bt cotton is the potential for
insects to evolve resistance to the insecticide. They insist that despite
its considerable value, Bt cotton should still be considered only one
component in the overall management of pests.

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