| A variety of GM squash did not turn out as well as hoped says a new report from Penn State. In the mid-1990's, the USDA okay'd a version of GM squash that was resistant to three of the most important viral diseases in cultivated squash.
Penn State professor of biology Andrew Stephenson and others did an experiment to see what would happen if the transgenes (the genes that had been modified) from cultivated squash spread into wild squash:
Stephenson and his colleagues James A. Winsor, professor of biology; Matthew J. Ferrari, research associate; and Miruna A. Sasu, doctoral student, all at Penn State; and Daolin Du, visiting professor, Jiangsu University, China, crossed the genetically modified squash into wild squash native to the southwestern United States and examined the resulting flower and fruit production. Unlike a lab experiment, the researchers tried to mimic a real world setting during their three-year study. The researchers then looked at the effects of the virus-resistant transgenes on prevalence of the three viral diseases, herbivory by cucumber beetles, as well as the occurrence of bacterial wilt disease that is spread by the cucumber beetles.
The results did not bode well for the GM trait. There are 2 other threats to the plants besides the viral diseases: cucumber beetles and bacterial wilt. Those two threats are linked, as the beetles spread the wilt by eating diseased plants and pooping out the bacteria on other plants. And guess what? The beetles prefer to eat the GM plants over the non-GM plants. That's because they prefer healthy plants to plants suffering from the virus. The end result is that the GM plants are safe from viral diseases but more susceptible to beetles and fatal bacterial wilt.
"Our study has sought to uncover the ecological cost that might be associated with modified plants growing in the full community of organisms, including other insects and other diseases," said Ferrari. "We have shown that while genetic engineering has provided a solution to the problem of viral diseases, there are also these unintended consequences in terms of additional susceptibility to other diseases."
See NPR's coverage on this same topic here.