Since its introduction in the mid-1990s,Bt corn,which is genetically modified to resist damage by insect pests, has been boosting agricultural production throughout the United States and the world. However, could this agricultural boon be an environmental bust?
That is the question posed in a new paper by a team of researchers including University of Notre Dame biologist Jennifer Tank. In the paper, Tank and her colleagues suggest that corn byproducts, such as pollen and crop detritus left behind after harvest, enter headwater systems draining agricultural crops and are subject to storage, consumption and transport to downstream water bodies.
Transgenic maize (corn) has been genetically engineering to produce its own insecticide, the Bacillus thuringiensis (Bt) delta endotoxin. The Bt toxin is poisonous to insect pests, most notably the European corn borer. One European corn borer per stalk across an entire field can reduce corn yield by an estimated five percent in first generation and two-and-a-half percent in subsequent generations.
As part of the licensing process for transgenic crops, the U.S. Environmental Protection Agency was responsible for testing and identifying potential environmental consequences from the planting of Bt corn,Tank said.The EPA concluded that transgenic corn posed no threat to aquatic ecosystems. We thought that more in-depth studies were needed to investigate the potential of Bt corn to influence aquatic ecosystems, given that small headwater streams frequently drain agricultural fields, especially in the Midwest.
Using field measurements obtained from streams draining farm fields in central Indiana, Tank and her fellow researchers showed that transgenic material from corn, such as pollen, leaves and cobs, do, in fact, enter streams in the agricultural Midwest.
Further laboratory feeding trials showed that these materials, when consumed by aquatic insects, such as stream caddisflies, close genetic relatives of the European corn borer, can cause reduced growth and possible increased mortality.
Our results suggest that the transgenic toxin in Bt corn pollen and detritus can affect species of insects outside the targeted pest,Tank said.
Caddisflies (and other aquatic insects) are important members of a stream ecosystem. They assist in the breakdown of organic matter and serve as a food resource for higher organisms, such as fish, birds and amphibians. In a larger context, aquatic insects are an important and necessary component to healthy, sustainable freshwater ecosystems. Widespread planting of Bt crops may have unexpected and unintended ecosystem-scale consequences in aquatic ecosystems located in close proximity to agricultural fields planted with genetically modified crops.
Our results suggest that there is the potential for effects in downstream water bodies, such as lakes and large rivers, because the transgenic materials that enter streams are stored and processed during baseflow, but may be exported during floods,Tank said.However, the ultimate fate of the materials is unknown and this is an important area for future study.
The researchers stress that their research should not be viewed as an indictment of farmers.
We do not imply that farmers are somehow to blame for either planting transgenic (Bt) corn, nor are they responsible for any unintended ecological consequences from Bt corn byproducts,Tank said.Farmers are, to a large extent, trapped in an agro-industrial system that, in order to stay competitive and profitable requires that they use the latest technological advances.
Rather, the study reveals that the prevailing previous assumption that transgenic corn byproducts would remain on fields overlooks the potential for these materials to enter and be dispersed by headwater streams.
Overall, our study points out the potential for unintended and unexpected consequences from the widespread planting of transgenic crops in the Midwest,Tank said.The exact extent to which aquatic ecosystems are, or will be, impacted is still unknown and likely will depend on a variety of factors, such as current ecological conditions, agricultural practices and climate/weather patterns.
The study appears in the Oct. 8 edition of the Proceedings of the National Academy of Sciences.
Emma J. Rosi-Marshall, who was a postdoctoral research fellow at Notre Dame at the commencement of the study and who is now an assistant professor at Loyola University, Chicago, is the lead author of the report. Other members of the research team include: co-principal investigators Todd Royer (assistant professor, Indiana University) and Matt Whiles (associate professor, Southern Illinois University); postdoctoral research associate Michelle Evans-White (Kansas State University); graduate students Natalie Griffiths (Notre Dame), Catherine Chambers (Southern Illinois), and Jillian Pokelsek (Loyola University, Chicago); and research assistant Mia Stephen (Notre Dame).The research study was funded by the U.S. National Science Foundation.
_ Contact: Jennifer Tank, Galla Associate Professor of Biological Sciences, 574-631-3976,_ " tank.1@nd.edu ":mailto:tank.1@nd.edu
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