A widely planted variety of genetically engineered corn has the potential to harm aquatic ecosystems. Pollen and other plant parts containing toxins from genetically engineered Bt corn are washing into streams near cornfields and harming a type of fly that is eaten by fish and amphibians, the study demonstrates.
Bt corn is engineered to include a gene from the micro-organism Bacillus thuringiensis, Bt, which produces a toxin that protects the crop from pests, especially the European corn borer. The research team led by Todd Royer, an assistant professor in the Indiana University School of Public and Environmental Affairs, found that consumption of Bt corn pollen, leaves and cobs increased mortality and reduced growth in caddisflies. aquatic insects related to the pests targeted by the toxin in Bt corn.
"Caddisflies," Royer said, "are a food resource for higher organisms like fish and amphibians. And, if our goal is to have healthy, functioning ecosystems, we need to protect all the parts." Caddisfly larvae are an important part of stream ecosystems, where they help control algae populations and provide food for fish and other creatures. In healthy streams, caddisflies are very common and their cases are found by the hundreds under rocks and logs.
Bt corn was licensed for use in 1996 and quickly gained popularity. By 2006, around 35 percent of corn acreage planted in the United States was genetically modified. "Every new technology comes with some benefits and some risks," he said. "I think probably the risks associated with widespread planting of Bt corn were not fully assessed." If there are unintended consequences of planting genetically engineered crops, Royer says farmers should not be held responsible. In a competitive agricultural economy, producers have to use the best technologies they can get, he said.
The study is published this week by the journal "Proceedings of the National Academies of Science, PNAS." Their research, conducted in 2005 and 2006 in an intensely farmed region of northern Indiana, measured inputs of Bt corn pollen, leaves and cobs in 12 headwater streams. They also found corn pollen in the guts of caddisflies, showing they were feeding on corn pollen. In laboratory trials, the researchers found caddisflies that were fed leaves from Bt corn had growth rates that were less than half those of caddisflies fed non-Bt corn litter.
Other crops such as potatoes and cotton also make use of Bt technology. When proponents of Bt technology list the benefits, they often say the Bt proteins in the crops will not kill beneficial insects. Royer and his team showed that claim is not accurate in the case of caddisflies.