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Bioengineered crops have mixed eco effects

Susan Milius

An unusually large research project in Great Britain has revealed that growing beets and canola that had been genetically modified to resist herbicides lowers the abundance of other plant species and certain insect groups that typically grow along with these crops. On the other hand, cornfields harboring genetically modified (GM) corn that resists herbicides have more weeds and insects than regular cornfields did, according to a series of reports in the Nov. 29 Philosophical Transactions of the Royal Society of London B.

The mixed results are from a set of experiments covering about 60 farm fields. The 3-year trials, funded by the British government, grew out of concerns that previous studies of the ecological effects of GM crops hadn't been big enough, says test coordinator Les Firbank of the Center for Hydrology and Ecology in Merlewood, England. Half of each test field was planted with the conventional crop and half with a GM version.

Areas growing GM beets and spring-planted canola ended up with weed-seed densities about 20 percent lower than those of areas with conventional crops. The GM portions of the beet fields also had fewer butterflies, but more springtails, which are small arthropods that feed on dead plants.

The GM cornfields, in contrast, hosted more insects and a more abundant population of weeds than conventional cornfields did. These differences are due to the somewhat weaker herbicide used in the GM cornfields, compared with the herbicide used on the conventional cornfields, the researchers suggest.

"There are many who are either strong supporters or firm opponents of GM crops, and each camp may be tempted to see support for their views in the findings," notes Semir Zeki, editor of Philosophical Transactions, in a commentary accompanying the reports.

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Letters:

Your article was such a wonderful example of reporter bias that I had to share it with my children. Growing genetically modified, herbicide-resistant beets and canola "lowers the abundance of other plant species and certain insect groups that typically grow along with these crops." But genetically modified, herbicide-resistant cornfields "have more weeds and insects than regular cornfields …" Gee, opposite effects, and both sound bad. Little wonder that "each camp may be tempted to see support for their views in the findings."

Rycke Brown
Grants Pass, OR

References:

Brooks, D.R. … L.G. Firbank, et al. 2003. Invertebrate responses to the management of genetically modified herbicide-tolerant and conventional spring crops. I. Soil-surface-active invertebrates. Philosophical Transactions of the Royal Society of London B 358(Nov. 29):1847–1862. Abstract.

Champion, G.T. … L.G. Firbank, et al. 2003. Crop management and agronomic context of the Farm Scale Evaluations of genetically modified herbicide-tolerant crops. Philosophical Transactions of the Royal Society of London B 358(Nov. 29):1801–1818. Abstract.

Firbank, L.G. 2003. The Farm Scale Evaluations of spring-sown genetically modified crops: Introduction. Philosophical Transactions of the Royal Society of London B 358(Nov. 29):1777–1778. Full Text.

Haughton, A.J. … L.G. Firbank, et al. 2003. Invertebrate responses to the management of genetically modified herbicide-tolerant and conventional spring crops. II. Within-field epigeal and aerial arthropods. Philosophical Transactions of the Royal Society of London B 358(Nov. 29):1863–1877. Abstract.

Hawes, C., … L.G. Firbank, et al. 2003. Responses of plants and invertebrate trophic groups to contrasting herbicide regimes in the Farm Scale Evaluations of genetically modified herbicide-tolerant crops. Philosophical Transactions of the Royal Society of London B 358(Nov. 29):1899–1913. Abstract.

Heard, M.S., … L.G. Firbank, et al. 2003. Weeds in fields with contrasting conventional and genetically modified herbicide-tolerant crops. I. Effects on abundance and diversity. Philosophical Transactions of the Royal Society of London B 358(Nov. 29):1819–1832. Abstract.

______. 2003. Weeds in fields with contrasting conventional and genetically modified herbicide-tolerant crops. II. Effects on individual species. Philosophical Transactions of the Royal Society of London B 358(Nov. 29):1833–1846. Abstract.

Roy, D.B., … and L.G. Firbank. 2003. Invertebrates and vegetation of field margins adjacent to crops subject to contrasting herbicide regimes in the Farm Scale Evaluations of genetically modified herbicide-tolerant crops. Philosophical Transactions of the Royal Society of London B 358(Nov. 29):1879–1898. Abstract.

Squire, G.R. … and L.G. Firbank. 2003. On the rationale and interpretation of the Farm Scale Evaluations of genetically modified herbicide-tolerant crops. Philosophical Transactions of the Royal Society of London B 358(Nov. 29):1779–1799. Abstract.

Zeki, S. 2003. The Farm Scale Evaluations of spring-sown genetically modified crops: Preface. Philosophical Transactions of the Royal Society of London B 358(Nov. 29):1775–1776. Full Text.

Further Readings:

Milius, S. 2003. When genes escape. Science News 164(Oct. 11):232–233. Available at Science News.

______. 2001. Bt corn risk to monarchs is "negligible." Science News 160(Sept. 15):164. Available at Science News.

______. 2000. Virtual skylarks suffer weed shortfall. Science News 158(Sept. 16):184. Available at Science News.

For more details on the crops and farm scale evaluation studies, go to DEFRA.

Sources:

Les Firbank
NERC Centre for Ecology and Hydrology, Merlewood
Windermere Road
Grange-over-Sands
Cumbria LA11 6JU
United Kingdom


From Science News, Volume 164, No. 20, November 15, 2003, p. 317.