June 5, 2008
UNIT 7: PlantsCaterpillar Parasites Not Hurt by Genetically Modified Plants
For many years, proteins from the Bacillus thuringiensis (Bt) bacterium have been used as an insecticide, primarily against moth and butterfly larvae. Since 1996, the Bt gene itself has been put into plants as a way to fight these pests. The cultivation of genetically-modified (GM) crops containing the Bt gene has been approved by the U.S. Environmental Protection Agency, and Bt crops have been approved for human consumption by the U.S. Food and Drug Administration. Nevertheless, little research has been done to evaluate how the GM plants affect other organisms.
Anthony Shelton and a team of researchers at Cornell University examined the effects of insecticides and the Bt protein on diamondback moth caterpillars and one of their natural parasites, the Diadegma insulare wasp. The researchers bred caterpillars that were resistant to either Bt insecticide, conventional insecticide, or organic insecticide. Next, they introduced the wasp into the caterpillars. The caterpillars were then fed one of two diets. One diet consisted of GM plants that express the Bt protein. The other consisted of non-GM plants that had been sprayed with one of the three insecticides.
The researchers found that caterpillars fed GM plants were killed by the parasitic wasps. Likewise, caterpillars that ate non-GM plants treated with Bt insecticides were also killed by the wasps. In contrast, caterpillars fed non-GM plants treated with traditional and organic insecticides to which they were resistant survived because the wasps were killed by the insecticides. From these data, Shelton and his team concluded that Bt plants both help control pest insects while also enhancing biocontrol and biodiversity.