February 3, 2014
Some GMO Bt Crops Do Not Affect Non-Target Insects
Brett Smith for redOrbit.com - Your Universe Online
Some crops have been genetically modified to produce toxins from the bacterium Bacillus thuringiensis (Bt) that protect them from insect pests. These modified crops have raised concerns that they may have unintended consequences for other organisms.
Two new studies have found that these crops have little or no effect on non-targeted insects and nematode worms.
In one of the studies, published in the February 2014 issue of Environmental Entomology, caterpillars known to be immune to the Bt proteins were fed Bt maize and Bt cotton. The caterpillars were then fed to two common, helpful, predatory insects – insidious flower bugs (Orius insidiosus), and big-eyed bugs (Geocoris punctipes) – over two generations and analyzed along with a different group of predators that ate caterpillars raised on non-Bt plants.
The scientists found the success, growth, adult mass, fecundity, and virility of the insect predators in both groups were comparable, despite whether they consumed caterpillars that feasted on Bt plants or non-Bt plants.
"This research demonstrates that the current Bt proteins used in corn and cotton crops globally do not harm Geocoris punctipes or Orius insidious, two important insect predators that help suppress pest populations on corn, cotton, and many other crops," said study author Anthony Shelton, a professor of entomology at Cornell University. "By using caterpillars resistant to the Bt proteins in this study, we were able to remove any 'host quality effects' that might have led to spurious misinterpretation of the results. This work demonstrated that the caterpillars consumed the Bt proteins, and the predators consumed the Bt proteins when they fed on the caterpillars, but they did not suffer any harm even over multiple generations."
The other study, published in the Journal of Economic Entomology, used comparable procedures to show that an essential nematode predator was not affected when it ate a different Bt protein. In this study, resilient caterpillars were given Bt broccoli and then subjected to Heterorhabditis bacteriophora, a helpful nematode that preys on insects.
The scientists found the virulence, reproductive potential, and timing of the surfacing of nematodes that ate Bt-fed caterpillars were not considerably affected, compared to nematodes that did not consume the Bt protein.
"This is the first report we are aware of in which a nematode predator has been tested in such detail against a Bt protein," Shelton said.
"Together, these two studies add to the scientific literature demonstrating that Bt plants can control targeted insect pests while not harming important natural enemies that help suppress pest species and maintain biodiversity in agricultural systems," he added.
Another study, published in Environmental Entomology, found that genetically-modified (GM) rice, cotton, and maize grown in South Africa did not affect the biodiversity of insects and related arthropods in GM crop fields – when compared to conventional crop fields. The study confirmed similar previous research conducted in China, Spain and the United States.
"The aims of the study were to compile a checklist of arthropods that occur on maize in South Africa and to compare the diversity and abundance of arthropods and functional groups on Bt maize and non-Bt maize," the authors wrote. "Results from this short-term study indicated that abundance and diversity of arthropods in maize and the different functional guilds were not significantly affected by Bt maize, either in terms of diversity or abundance."