Genetically modified (GM) plants that use Bt (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 Bt insecticidal proteins
are not toxic to a parasite that lives inside the caterpillar of the
diamondback moth, a devastating worldwide vegetable pest. It was published
in the May 27 issue of the online scientific journal PLoS One.

"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 Bt," 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 Bt
plants are a win-win situation to control pest insects and to enhance
biocontrol and biodiversity."

The Bt bacterium, which is not harmful to humans, has been used for
decades as a leaf spray and since 1996, in GM plants, a method that has
proven much more effective and is now more widely used. Both uses are
approved by the U.S. Environmental Protection Agency. In 2007, Bt corn and
cotton plants were grown in 22 countries on 104 million acres, according to
Shelton.

"Few studies have examined the effect of Bt 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 Bt proteins on the
caterpillar and parasite, the Cornell researchers isolated and bred strains
of caterpillars that were resistant to Bt 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 Bt 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 Bt-sprayed
plants or Bt plants, the parasite was not affected and killed its host
caterpillar when it emerged as an adult wasp, showing that Bt plants are not
toxic to the parasite.

Other Cornell researchers involved in the study include Elizabeth
Earle and Jun Cao from the Department of Plant Breeding and Genetics and
Jian-Zhou Zhao and Hilda Collins from the Department of Entomology. The work
was supported by a grant from the USAID Program for Biosafety Systems.


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