Bt and H2O

Perspectives: Research and Creative Activities at SIUC, Spring 2008

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Bt and H2O

Could transgenic corn have unintended consequences downstream?

The genetically modified corn grown by many U.S. farmers might harm life in the streams where parts of the plants end up each year, an SIUC scientist says.

Matt Whiles, associate professor of zoology, is part of a team of stream ecologists from four universities studying the effects of Bt corn on the waterways near agriculture fields. The group's first paper on the subject garnered international attention when it appeared in the Proceedings of the National Academy of Sciences last fall.

Bt corn is engineered to incorporate a bacterial gene that produces a toxin poisonous to the European corn borer and other pests. This transgenic corn is popular with farmers because they are able to grow healthier crops using less insecticide. In recent years, however, the potential for ecological side effects from transgenic crops has come under greater scrutiny.

The scientists examined whether material from Bt corn plants—everything from pollen to husks and cobs—might have unintended impacts on the stream food chain as aquatic insects use the material for food.

"We all got interested in this because there weren't many people looking at possible effects of transgenic crops on aquatic systems," says Whiles. He joined researchers from Indiana University, the University of Notre Dame, and Loyola Chicago University in doing the four-year study, which wraps up this year. The National Science Foundation funded the project with a $580,000 grant.

The research focused on caddisflies, small insects closely related to pests targeted by Bt corn toxin. Caddisfly larvae are aquatic; they break down the coarse biomaterial deposited into streams, making nutrients available to other creatures.

Whiles and graduate student Catherine Chambers found caddisfly larvae have slower growth rates when feeding on Bt corn crop debris than when feeding on the non-modified variety. Because smaller insects tend to have fewer eggs, it's possible their numbers could decline over time, which might have an overall negative effect on stream food webs.

"We're beginning to speculate some at that point—all we're showing now is slower growth," Whiles says. "But it could have a negative effect because caddisflies...[are] an important link in the food chain, and they are in turn a very important food source for fishes, amphibians, and other life forms."

One of the challenges the researchers faced is the fact that agricultural streams are already highly impacted by other substances, such as nutrients, pesticides, and sediments. To try to separate out the relative impacts of Bt corn debris, the researchers strove to record real-life conditions in the field.

Working on 12 streams in northwest Indiana, the researchers suspended adhesive microscope slides over the streams they studied, to capture pollen grains and estimate exactly how much pollen was entering the waterways. They used nets to measure how much coarse material entered the streams and in some cases measured how far it traveled.

"We built various structures and traps along the streams," Whiles says. "We'd also walk the streams, pull material out, and weigh it."

In the lab, the researchers fed caddisfly larvae modified and non-modified corn plant crop debris from the fields surrounding the streams they were studying, and then measured the growth and survival of the insects.

It's too early to say whether Bt corn is having any significant effects on the aquatic environment. But the study shows that the potential exists for unintended consequences. The group wants next to examine how Bt corn debris moves through waterways—including into lakes and rivers—and further affects aquatic insects.

"What we have is some evidence of unforeseen impacts," Whiles says.

"What it means is that there is more to examine here than has been considered yet."

—by Tim Crosby