October 09, 2007

Transgenic corn may affect aquatic insects

by Tim Crosby

CARBONDALE, Ill. -- The genetically modified corn used by many grain farmers might harm life in the steams where parts of the plants end up each year, a Southern Illinois University Carbondale researcher said.

Matt R. Whiles, associate professor of zoology in the College of Science at SIUC, 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 just released its first paper on the subject, titled "Toxins in transgenic crop byproducts may affect headwater stream ecosystems," on Monday (Oct. 8).

The group, funded by a grant from the National Science Foundation, examined whether the genetically modified corn plant debris — everything from pollen to husks and cobs — might have unintended impacts on the stream food chain as aquatic insects use it for food. Genetically modified corn such as Bt corn is engineered to create a toxin aimed at destroying the European corn borer, a moth larvae, and other pests that typically feed on corn crops.

The crops are popular with farmers because they are able to grow healthier crops using less pesticide. In recent years, however, some have criticized the use of genetically modified crops, saying they might hurt the ecosystem.

"We all got interested in this because there weren't many people looking at possible effects of transgenic crops on aquatic systems," said Whiles, who joined researchers from Indiana University, the University of Notre Dame and Loyola Chicago University in doing the study. "The added dimension in studying streams is not only the potential adverse effects there but also that they move materials across the landscape and that's what we're going to be looking at next."

The current research focuses on caddisflies, small insects that break down the coarse biomaterial deposited into streams and provide an important food source for other stream life. The researchers chose caddisflies because they are closely related to pests targeted by Bt corn toxin.

Whiles and his graduate student, Catherine Chambers, found caddisflies have slower growth rates when feeding on Bt corn crop debris than when they feed on the non-modified variety. Because smaller insects tend to have fewer eggs, Whiles said 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 said. "But it could have a negative effect because caddisflies and other aquatic insects are doing a variety of things in streams. One of the main things they do is recycling of materials, such as nutrients. They break down the coarse materials and make them available to other creatures, so they're an important link in the food chain, and they are in turn a very important food source for fishes, amphibians and others 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. "It's hard to filter out what the Bt corn debris' relative impacts are," Whiles said.

Still, the four-year study's results point toward the conclusion that genetically modified crops do have some unintended effects on the environment, Whiles said.

"The big question we're facing now is the magnitude of these effects," he said. "We don't have a handle on that."

To ensure the study's validity, the researchers strove to record real-life conditions mostly in the field, rather than recreate them in a laboratory. Working on 12 streams in northwest Indiana, the researchers suspended adhesive microscope slides over the streams they studied, to capture and estimate exactly how much pollen enters the waterway. They used nets to measure how much coarse materials entered the stream and some cases marked some and measured how far it traveled.

"We built various structures and traps along the streams," he said. "We'd also walk the streams, pull material out and weigh it. We'd take the slides and count the pollen grains on them and from that you could figure out the pollen input rate."

In the laboratory, the researchers fed caddisflies modified and non-modified corn plant crop debris from the actual fields surrounding the streams they were studying and measured the growth and survival of the insects.

The NSF provided $580,000 for the study, which began in 2004 and is due for completion in 2008. SIUC received about $118,000 of that initial amount.

The group now is writing a proposal to further study the issue, looking specifically at how the material moves through the waterways and further impacts aquatic insects. The study suggests transgenic plant material could also affect other bodies of water, such as lakes and rivers after floods wash them downstream.

Whiles said it's too early to determine genetically modified crops' effect on the aquatic environment, but it's clear there is a potential for unintended consequences.

"At least for what we're looking at the jury is still out," he said. "What we have is some evidence of unforeseen impacts. What it means is that there is more to examine here than has been considered yet."