GM crops go walkies

Abstract

Two recent reports revive concerns about the implications of large-scale use of genetically modified (GM) crops. The Mexican government announced that GM DNA could be detected in seeds collected from endogenous corn varieties at 15 different locations, the New York Times reports. So far, it's unclear what the source of the DNA is, but experts think it likely that transgenic ‘Bt’ corn has interbred with local plants. Bt corn carries a bacterial toxin gene that protects the plant from the European corn borer pest. Considering that Bt corn, or indeed any GM crop, cannot be grown in Mexico, the findings suggest that geography and plant variety impose smaller barriers for transmission of transgenes than previously anticipated. Bt corn was also a focus of attention in six papers published on-line in PNAS on 14 September (Zangerl et al., Sears et al., Hellmich et al., Pleasants et al., Stanley-Horn et al., Oberhauser et al.). Previous work had indicated that, under laboratory conditions, Bt toxin not only killed European corn borers but also harmless black swallowtail caterpillars. Here, the authors report that Bt corn pollen can contaminate neighboring plants with doses high enough to kill the swallowtail caterpillars. However, the studies also show that Bt toxin rarely exceeds lethal doses in the fields and poses only a minor threat to the ecosystem. Moreover, the harmful Bt corn variant Bt176 is only a prototype – new Bt corn variants are not harmful, and Syngenta, the producer of Bt corn, has already taken Bt176 off the market. J.d.B.