Pest-Resistant Crops Better Than Insecticide Use, Analysis Says

Amitabh Avasthi
for National Geographic News

June 7, 2007

A type of genetically modified (GM) crop that resists pests may be a better alternative to farming with insecticides, a new report says.

These crops contain a gene from Bacillus thuringiensis, or Bt, a common bacterium found in soil.

The gene helps the plants produce proteins that are toxic to certain insects. Some Bt crops are designed to only kill caterpillars, others to only kill beetles. (Learn how scientists insert genes into plant and animal DNA.)

The Bt crops did not seem to kill all the insects that come into contact with them, whereas insecticides do.

"Insecticides generally have a broad spectrum, and they kill lots of different types of insects, not just the pests," said study author Michelle Marvier of Santa Clara University in California. Bt crops, Marvier said, are much more specific in their action.

"Ideally, it would be best to see a reduction in the target pest species, but not much of a reduction in the other species that live on and around farms," Marvier said.

However, Marvier and colleagues caution that the study looked only at corn and cotton and that the findings may not apply to all GM crops.

The Good Guys

Researchers point out that most studies by industry, which are submitted to government agencies such as the U.S. Environmental Protection Agency and the U.S. Department of Agriculture, have been poorly replicated and therefore might have missed important side effects of the GM crops.

So Marvier and her colleagues, who are not associated with the U.S. government or industry, analyzed the results of 42 field trials to discover the effect of Bt crops on "nontarget pests"—the insects not harmful to crops.

"The nontarget invertebrates are the 'good guys,'" Marvier said.

"These are the honeybees, the earthworms, the ladybird beetles, and so on. They may also include some plant-feeding insects, but even these are not the ones that Bt is meant to kill."

Their results suggest that, for the most part, Bt crops have less of an effect on ladybird beetles, earthworms, and honey bees than do insecticide sprays.

(See related: "Engineered Rice Cut Pesticides, Illnesses, Study Says" [April 29, 2005].)

However, when the Bt crops were compared to similar non-Bt crops that had not been sprayed with insecticide, some of the nontarget insects were less abundant in fields of Bt crops.

LaReesa Wolfenbarger is a research biologist at the University of Nebraska at Omaha who was not involved in the study.

The meta-analysis—a review of several studies that appears tomorrow in the journal Science—may make the findings more credible than a single study, she said.

But Wolfenbarger cautioned that the effects of Bt crops on nontarget organisms depend on agricultural practices, such as the use or nonuse of insecticide in addition to Bt.

Insecticides may or may not be applied when growing corn or cotton, the study noted.

"I find this to be a very important point—namely that the agricultural practices associated with the crops greatly influence the ecological impacts," Wolfenbarger added.

Informing the Public

Study author Marvier admitted that the findings would not be widely applicable to Bt-producing crops and other GM crops.

"Just because we saw certain effects or lack of effects with Bt crops does not mean that similar effects would exist in herbicide-tolerant crops or other types of pest-resistant crops," she said.

Marvier hopes the database she has created will be adopted by regulatory agencies.

But if companies were required to enter data from their risk assessment studies directly into such a database, it would be easier for regulators and the general public to spot gaps or errors, she said.

"This could go a long way toward making the process more transparent, and hopefully reassuring the public."

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