Cornell
University

The first of the three studies they comment on was led by John E. Losey, Cornell assistant professor of entomology. This study of the effect of Bacillus thuringiensis (Bt) corn on the monarch butterfly "can only be considered a preliminary laboratory study," they write.

In the May 20 issue of Nature, Losey and his colleagues reported that pollen from commercial corn, genetically engineered to produce a bacterial toxin to protect it against European corn borers, kills monarch butterfly larvae in laboratory tests. While Shelton and Roush note that this result was expected under such laboratory test conditions, they question whether this test was realistic.

"If I went to a movie and bought a hundred pounds of salted popcorn, because I like salted popcorn, and then I ate those the salted popcorn all at once, I'd probably die. Eating that much salted popcorn simply is not a real-world situation, but if I died it may be reported that salted popcorn was lethal," Shelton said in an interview. "The same thing holds true for monarch butterflies and pollen.

Scientists have a duty to be incredibly responsible for developing realistic studies. Scientists need to make assessments that are pertinent to the real world."

In the second study discussed in the article, researchers at Kansas State University reported in Science that they had discovered corn borer resistance to Bt toxins. Shelton and Roush question the methodology used in the study, "including that the authors did not demonstrate that resistance was actually to the same Bt toxin as in the plant or that the insects could survive on the Bt plant." Even so, they write, "this questionable laboratory study has generated considerable debate over whether the present resistance management policy should be overturned."

In another recent issue of Nature, a University of Arizona study showed that the pink bollworm's resistance to Bt-cotton was recessive in inheritance, but the paper questioned whether resistant bollworms developed more slowly than susceptible bollworms. This could possibly knock out random mating and dilute the insect's resistance in the field. "We hope that the take-home message won't be converted to another premature claim that Bt crops are doomed," Shelton and Roush say in their commentary.

Since the release of the monarch butterfly study, write Shelton and Roush, companies that make the genetically engineered agricultural seed have been confronted by freezes on the approval process for Bt transgenic corn by the European Commission and by "possible trade restrictions by Japan." In the United States, there have been calls for a moratorium on the further planting of Bt-corn.

In discussing the Cornell monarch butterfly report, Shelton and Roush voice their surprise that a "previous and more relevant and realistic study has been largely overlooked." While the Cornell laboratory study showed high mortality among monarch larvae that ingested genetically engineered pollen, an Iowa State University study by Laura Hansen and John Obrycki showed low mortality even when Monarch larvae were fed milkweed that had the highest levels of Bt pollen that would be encountered in the field. Shelton and Roush note that it is unlikely that these high Bt pollen levels would be encountered by the insects in the field, and they say that "few entomologists or weed scientists familiar with the butterflies or corn production give credence to the Nature article."