For many farmers, the tried-and-true method to ridding their crops of insects is to spray the fields with chemical pesticides. Yet an increasing number of farmers who grow cotton and corn are turning to genetically modified plants that kill pests with the help of a bacterium gene. New research suggests that the gene may even be better for the environment than traditional methods of pest control.

A review of previous research (a meta-analysis), published in the journal Science last month, looked at 42 studies of cotton and corn crops genetically modified with an insecticide gene called Bt. Individually, the studies were too small to adequately determine significant effects; but collectively, researchers found that plant fields with the inserted Bt gene actually have more bugs than fields where farmers sprayed pesticides. Rather than killing all the bugs in the field as pesticides do, the Bt gene targets specific species. Although fields that didn’t use pesticides or GM crops displayed the most bug biodiversity, the study showed that Bt crops don’t require as many harmful pesticides that leach into soil and pollute lakes and streams.

“We were really just trying to lay out what are the pros and what are the potential cons,” of Bt crops on invertebrates like bees and earthworms that the gene doesn’t target, says Michelle Marvier, a biologist from Santa Clara University and the primary researcher for the study.

For the last 10 years, companies have been introducing the Bt gene into crops, largely to eliminate a caterpillar that eats corn stalks. Since then, many people—including some environmental groups like Greenpeace—have protested against GM crops, arguing that they could decrease biodiversity and harm human health. But for scientists aware of the benefits of Bt crops, this study “really confirms a lot of studies that have been done since these plants came out,” says Tony Shelton, a professor of entomology at Cornell University who was not involved in the study.

But Bt crops may pose a problem to people opposed to eating GM foods. The inserted genes could transfer to non-GM crops through natural pollination, especially as more and more farmers plant modified seeds. But what people may not realize is that many of the vegetables we eat have been modified for centuries, says Steve Naranjo, an entomologist at the US Department of Agriculture’s Arid-Land Agricultural Research Center who was on a working group that reviewed the paper. “Native corn doesn’t look anything like what’s growing through the Midwest,” he says. Adding a single gene to a plant is “a lot less Frankenstein than you might think.” He also acknowledges that the debate can be more emotional than scientific.

Marvier says she knows that the meta-analysis only scratches the surface and Bt crops may have effects on other animals and the agricultural environment. It might take many more studies to convince the public that some GM crops aren’t bad for biodiversity.

To aid further research, scientists involved in the analysis compiled a database of many studies on Bt crops, so anyone can access them. The database now includes more than 170 studies. “The authors of this have done a real service to the scientific community,” says Naranjo. “There’s just a lot of value in the database that I think will keep people busy for a long time.”

Although the study’s conclusion provides validation of Bt crops for some researchers, scientific information alone may not be enough to end the controversy for the general public. Still, scientists continue to gather data about the environmental benefits of using Bt crops as a biological control. “There are activists who can raise questions,” says Shelton. “But from a scientific standpoint, I don’t think there’s any question that Bt plants have been a great advantage for our environment.”

Story by Susan Cosier. This article originally appeared in Plenty in July 2007.

Copyright Environ Press 2007.

Study: Modified crops may be better
Genetically modified plants that kill pests with the help of a bacterium gene may even be better for the environment than traditional methods.