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September 22, 2008

GM cotton grown in China has wider insecticidal benefits than on target crop

According to a study published this week in "Science," genetically-engineered cotton planted near conventional crops may help protect the regular plants from bugs. The researchers say the finding could potentially protect a range of crops over millions of hectares. VOA's Jessica Berman reports.

The number one threat to cotton crops worldwide is the bollworm, a moth whose larvae feed on the plant's leaves.

Researchers responding to the threat 20 years ago genetically engineered a cotton plant that produces a toxic protein, called Bacillus thuriniegensis. The protein kills the moth larvae, but is engineered to be safe for humans and animals. Globally, an estimated 14 million hectares of so-called Bt cotton are grown today.

In a study reported this week in Science, researchers report that not only are bollworms destroyed by Bt cotton plants, but the plants appear to benefit unmodified crops that are nearby.

Chinese and American researchers monitored a number of different crops, including peanuts, soybeans, corn and vegetables, between 1992 and 2007 in six provinces in northern China (Hebei, Shandong, Jiangsu, Shanxi, Henan, and Anhui), which covered 38 million hectares of farmland.

Investigators found that three million hectares of Bt cotton planted among the other crops drove down populations of bollworm pests so much there were fewer moths to infest adjacent plants, according to Anthony Shelton an entomologist at Cornell University in Ithaca, New York and an advisor on the Science paper.

"So, basically what has happened is there has been a regional suppression of the cotton bollworm over a number of different provinces in China because this Bt cotton is acting like a sink and it is a dead end for them," he said.

While the bollworm is primarily a threat to cotton plants, there are lesser insect threats to it and surrounding crops.

Some experts, including the authors, have expressed concern that an over reliance on Bt technology has led to a reduction in the use of sprayed pesticides that are effective against a range of insects.

In particular, Shelton notes that mirids, which are leaf eating insects, are becoming a bigger problem in the Bt cotton.

"I do not want to downplay it, but at the same time when things are put into perspective, the benefits for overall pest population suppression of Bt cotton have been tremendous and the mirids are a much smaller player in the pest management program," he said.

There have been other concerns that the bollworm could become resistant to the toxin produced by Bt cotton. Shelton says that is something to watch out for.

But scientists say the success of Bt cotton in protecting unmodified crops could lead to other Bt crops such as rice.



Genetically-modified cotton which has been altered to include an insecticide can help cut pests in neighbouring fields of ordinary crops. Cotton grown in China that has been genetically modified to produce the insecticide, Bt, had a wider impact on insect pests than the target crop, a discovery which is welcomed by the agriculture lobby and criticised by environmentalists.

Drs Kongming Wu and colleagues analysed data from 1997, when the GM cotton was commercialised, to 2007 about the agriculture of Bt cotton in northern China, and compared them to data on pest populations in the region.

The use of Bt cotton reduced the populations of cotton bollworms, a problematic pest for Chinese farmers, cutting the need for pesticides by around half, and reduced the insects on neighbouring crops.

The insect usually moves between crops, after first invading cotton.

"Bt cotton kills most of the larvae of the second generation and accordingly works as a dead-end trap crop for cotton bollworm population," said Dr Wu.

"This case study for Bt cotton also implies that other Bt crops such as Bt rice may have a great potential value for agricultural practices in China," he added.

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 lethal to caterpillars of moths and butterflies. However, major challenge to the success of Bt cotton in China remains the potential for insects to evolve resistance to it.

Dr Wu and colleagues recommend that Bt cotton should be considered only one component in the overall management of pests. Environmentalists will argue that the study shows GM crops could disrupt neighbouring ecosystems but Dr Wu said: "There are two kinds of ecological balances, one is balance for all wild species, another is for agricultural production.

"Bt cotton is good for ecological balance in an agricultural system. If environmentalists want to get an ecological balance for all wild species, this means we need to protect wild ecology and risk food shortages."

Cotton bollworm is one of the most important insect pests of cotton, corn, soybean, peanut and vegetables. In 1992, this pest cut China's cotton yield by almost one third. The outbreaks resulted in overuse of chemical insecticides which increased cost, polluted environmental, and bring a series of economic, ecological and social issues.

Dr. Jian-Zhou Zhao, a co-author, 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 1990s. 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."

Commenting on the study, Friends of the Earth’s GM campaigner, Clare Oxborrow said: "It's not surprising that the number of target pests has fallen - the GM cotton contains a toxin poisonous to them.

"This study tells us nothing about the wider ecological impacts of growing Bt cotton, such as the impact on non-target species. It also fails to identify the impact on crop yields and the overall level of pesticide-use.

"This limited study must not be used to justify the cultivation of GM cotton – or any other GM crop."

The Telegraph

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