Monarch Bt-corn paper questioned


reviewed Scientific Correspondence paper indicating that transgenic pollen kills larvae of the monarch butterfly provoked contrasting responses around the world. While environmental interest groups seized on the findings as demonstrating the harmful effects of genetically modified crops on “nontarget” species in agricultural regions, plant scientists and representatives of life science companies among others criticized the work as premature, incomplete, and unconvincing. In the controversial experiments, monarch larvae fed on milkweed leaves dusted with pollen from N4640-Bt corn (a commercial variety containing a gene for an insecticidal Bacillus thuringiensis protein as a defense against infestation with the European corn borer) ate less, grew more slowly and had higher mortality than those fed plain leaves or leaves dusted with pollen from a nontransgenic corn line. After four days, survival of larvae exposed to N4640-Bt corn was 56% compared with 100% for the pollen-plus and pollen-minus controls. The monarch, whose larvae feed exclusively on milkweed leaves, is regarded as a particularly sensitive indicator of environmental disturbance. Critics of the work have particularly highlighted a number of weaknesses of the paper. The first is that it is unsurprising that a lepidopteran species such as the monarch should be affected when fed plant material that contains a protein used precisely because of its lepidopteran-specific killing properties. Willy De Greef, the worldwide head of regulatory and government affairs for Novartis Seeds (Basel, Switzerland), the company that developed the N4640-Bt variety, would have liked to see a greater stringency with respect to the Cornell University (Ithaca, New York) group’s experiments. The forced feeding of a potentially toxic compound to larvae does not really represent the reality in the field. More convincing, he says, would have been the results of “choice” experiments. where, as in the field, the monarch larvae are exposed simultaneously to milkweed leaves with and without Bt-maize pollen. The preliminary Cornell experiments reported in Nature indicate that the presence of both transformed and untransformed pollen reduces leaf consumption by the larvae, something that might be expected to have a bearing on larval survival. De Greef says that the “choice” experiments would explore the monarch’s pollen avoidance strategies. The second major criticism is that the experiments were poorly quantified. At the European Plant Biotechnology Network’s Phytosfere meeting held in Rome at the beginning of June, a show of hands in a plenary discussion indicated that the majority of delegates resoundingly rejected the work’s validity. “If I had measured out pollen by dropping it onto leaves with a spatula [the method the Cornell researchers used]”, said one delegate from the Netherlands, “I would expect to be chopped into little pieces during peer review.” John Losey, the lead author on the paper, admits that the methods used were “not stringently quantitative”, but he says that there is “no reason to believe that there would be a systematic error in one direction or the other.”

DOI: 10.1038/10834

Cite this paper

@article{Hodgson1999MonarchBP, title={Monarch Bt-corn paper questioned}, author={John Mc B Hodgson}, journal={Nature Biotechnology}, year={1999}, volume={17}, pages={627-627} }