B.t. not Bad for Beneficial Bugs
Genetically modified (GM) plants that use B.t. (Bacillus thuringiensis), a common soil bacterium, to kill pests won't harm the pests' natural enemies, according to new research by Cornell entomologists. That is welcome news for ecologists and farmers in the debate over GM plants. Much of the debate surrounding the use of GM crops focuses on their effect on organisms that aren't pests.
The research showed that GM plants expressing B.t. insecticidal proteins are not toxic to a parasite that lives inside the caterpillar of the diamondback moth, a devastating worldwide vegetable pest. “The conservation of parasites is important for enhancing natural biocontrol that will help suppress pest populations as well as reduce the potential for the pest insects to develop resistance to the B.t.,” explained Anthony Shelton, Cornell professor of entomology at the New York State Agricultural Experiment Station in Geneva, N.Y., who conducted the study with postdoctoral associate Mao Chen. “Our studies make it clear that B.t. plants are a win-win situation to control pest insects and to enhance biocontrol and biodiversity.”
The B.t. bacterium, which is not harmful to humans, has been used for decades as a leaf spray in organic and conventional agriculture and since 1996, in GM plants, a method that has proven much more effective and is now more widely used. “Few studies have examined the effect of B.t. plants on parasites of caterpillars, but some of them have reported negative impacts,” said Chen, noting that the new research suggests that those negative findings were likely due to testing methods. To separate out the effect of insecticides and B.t. proteins on the caterpillar and parasite, the researchers isolated and bred strains of caterpillars that were resistant to B.t. or a conventional or organic insecticide. Then the caterpillars were parasitized with a wasp that kills the caterpillar in nature. The resistant caterpillars were then either fed GM plants expressing the B.t. protein or non-GM plants sprayed with the Bt protein, conventional insecticides, or organic insecticides. The parasitized caterpillars that ate plants treated with conventional and organic insecticides to which they were resistant, survived and developed into moths because the parasite was killed by the insecticide the caterpillar ingested. However, when the caterpillar fed on the B.t.-sprayed plants or B.t. plants, the parasite was not affected and killed its host caterpillar as it emerged as an adult wasp, showing that B.t. plants are not toxic to the parasite. (Checkbiotech, 6/4/08).
