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, the study says, citing U.S. Department of Agriculture data.
Before licensing Bt corn, the U.S. Environmental Protection Agency conducted trials to test its impact on water biota. But it used Daphnia, a crustacean often used for toxicity tests, and not insects that are more closely related to the target pests, Royer said.
'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.
Funded by the National Science Foundation, the study is published this week by the journal 'Proceedings of the National Academies of Science, PNAS.'
There was a public outcry over the use of Bt corn in 1999, when a report indicated it might harm monarch butterflies. But studies coordinated by the federal Agricultural Research Service and published in PNAS concluded Bt corn was not a significant threat to monarchs.
Around that time, Royer said, he and his colleagues wondered whether the toxin from Bt corn was getting into streams near cornfields, and, if so, whether it could have an harmful impact on aquatic insects.
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, using litter traps to collect the materials. 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. They also found that a different type of caddisfly had significantly increased mortality rates when exposed to Bt corn pollen at concentrations between two and three times the maximum found in the test sites.
Royer said there was considerable variation in the amount of corn pollen and byproducts found at study locations and there is geographical variation. Farmers in Iowa and Illinois, for instance, are planting more Bt corn than those in Indiana. The level of Bt corn pollen associated with increased mortality in caddisflies, he said, 'could potentially represent conditions in streams of the western Corn Belt.'
There are four bands of Bt corn seed available commercially - YieldGard from Northrup King (Novartis); YieldGard2 from Monsanto; YieldGard Rootworm from Monsanto; and Herculex from Pioneer DowAgra-Sciences.
Other crops such as potatoes and cotton also make use of Bt technology. By 1999, 29 million acres of Bt corn, potato and cotton were grown globally.
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.
Other principal investigators for the study, titled 'Toxins in transgenic crop byproducts may affect headwater stream ecosystems,' were Emma Rosi-Marshall of Loyola University Chicago, Jennifer Tank of the University of Notre Dame, and Matt Whiles of Southern Illinois University.