FEATURE ARTICLE
Ecology of Transgenic Crops
Genetically engineered plants might generate weed problems and affect nontarget organisms, but measuring the risk is difficult
Michelle Marvier
Setting Standards for Sampling
Additional evidence for worrisome experimental practices exists in a Monsanto petition (#94-257-01p) that was submitted for a Bt potato. In this case, investigators repeated experiments only when a statistically significant nontarget effect of Bt toxin was detected. If no effect was detected, the investigators did not repeat the experiment. This methodology strongly favors finding no effects even if a true effect exists. Essentially, this method resembles throwing out data—although somewhat less blatantly—unless it yields the desired answer.
In contrast to the studies submitted to support USDA petitions, some published studies—relying on larger sample sizes and more stringent methodology—documented significant impacts of Bt toxin on nontarget species. For example, Angelika Hilbeck of the Swiss Federal Research Station for Agroecology and Agriculture and her colleagues found that green lacewings, which are beneficial predatory insects, experienced 62-percent mortality when fed a diet of pests reared on Bt corn, but only 37-percent mortality when fed pests reared on nontransgenic corn. Hilbeck's group followed the fates of 200 individual green lacewings per treatment. In addition, the authors emphasized that, because Bt toxin is expressed continuously in the crop, it is essential to test for effects over the entire life span of the organisms of concern. On the other hand, Carol Pilcher, then a graduate student at Iowa State University, found no effect of Bt toxin on nontarget predators, despite using large numbers of samples.
Getting a better understanding of any potential dangers of transgenic crops, especially to untargeted organisms, will require a consistent approach to studies in this field. Currently, the EPA is developing guidelines for testing the effects of transgenic plants on collateral organisms. A Scientific Advisory Panel met in December 1999 to review the draft EPA guidelines and recommended the following: "The Agency [EPA] should consider how the data will be used and establish an acceptable level of statistical power. Based on these decisions, appropriate tests and sample sizes can be determined." (The entire report is available online at http://www.epa.gov/scipoly/sap/1999/index.htm.)
This panel's advice hits the target: No single prescribed sample size fits all cases. As shown above, however, one can easily calculate the necessary sample size after collecting some pilot data. Although it is popular these days to complain about federal regulations and interference, the EPA's recognition of the importance of statistical power makes clear the benefits of governmental guidelines. If the EPA does not step forward and set standards for experimental design, some companies would likely continue to rely on extremely weak tests of nontarget toxicity.
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