Chronicle Online e-News
New study shows that transgenic plants don't hurt beneficial bugs
http://www.news.cornell.edu/stories/June08/SafetyofBt.mf.ht
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June 3, 2008
By Marissa Fessenden
cunews@cornell.edu
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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Marissa Fessenden '09 is an intern with CALS Communications.
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