2-Plants: Transgenic cotton controls pest in Arizona
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TITLE: Transgenic cotton controls pest
SOURCE: United Press International Science News, USA, by Charles Choi
DATE: Feb 3, 2003
------------------ archive: http://www.gene.ch/genet.html ------------------
Transgenic cotton controls pest
TUCSON, Ariz., Feb. 3 (UPI) -- Genetically engineered cotton in Arizona,
grown using a strategy mandated by the Environmental Protection Agency,
is effectively controlling a common crop pest without causing increased
pesticide resistance, a study released Monday concluded.
The findings suggest transgenic crops could help the environment through
reduced insecticide use.
"Transgenic crops have potential to improve agriculture, but we must be
careful when we use them," researcher Yves Carriere, an evolutionary
ecologist at the University of Arizona in Tucson, told United Press
Repeated experience with pesticides reveals insects frequently and
rapidly evolve resistance against such compounds. While the insecticides
may kill off nearly all members of a given pest species, a few lucky
insects might have a natural insecticide resistance they spread to all
Carriere said pesticides have come a long way in environmental
friendliness since DDT but it is best to limit their use in case of any
"Also, when you use too much insecticide, you kill off the natural
enemies of any pests," Carriere explained. "More than 40 species of
herbivores feed on cotton, but only three or four of them are
significant, with the rest controlled by other things like natural
enemies. You apply too much insecticide, and the pests that were not a
problem become a problem."
One group of genetically engineered crops designed to reduce pesticide
use are so-called Bt crops, which produce a toxin made by a gene taken
from the natural soil microbe Bacillus thuringiensis. Transgenic crops
now cover more than 150 million acres worldwide. However, little is known
about their long-term consequences and the possibility such crops quickly
would be rendered useless once insects evolved resistance against them.
"In the laboratory, we have easily grown pink bollworms resistant to Bt
cotton in the laboratory," Carriere said. "So their relatives in the
field have a potential to evolve resistance that's quite high."
To minimize the risk of evolved resistance against Bt crops, the EPA in
1995 required all growers of Bt cotton to plant crops that do not
generate toxins alongside Bt crops. Insects vulnerable to such toxins are
kept alive in such clean fields to mix their insecticide-susceptible
genes with resistance traits to dilute and therefore delay the evolution
of resistance among their descendants.
"The EPA was right in doing so," Carriere explained. "This refuge
strategy is absolutely needed to delay the evolution of resistance."
Carriere and colleagues looked at the population density of pink
bollworm, a key cotton pest, across 300,000 acres of cotton in Arizona
over a 10-year span -- five years before Bt cotton was deployed and five
years after. More than 1,000 traps containing sex pheromones were
deployed to capture insects for study.
Findings reported Monday online by the Proceedings of the National
Academy of Sciences show that investigators found up to a four-fold
decrease in pesticide applications following the introduction of Bt
cotton. This led to an up to six-fold decrease in pink bollworm
This steady decline suggests the pink bollworm soon could be eliminated
as a key pest, Carriere said.
"A key pest has never been transformed into a non-important pest with
insecticides," he explained. His team will continue to track pink
Jane Rissler, senior staff scientist for the Union of Concerned
Scientists in Washington, was pleased to see these results.
"The Arizona scientists deserve a lot of credit for their systematic
study of the use of Bt cotton," she said. "Frankly, this is what we'd
like to see in many other places in the country."
Rissler and Carriere both feel these results do not necessarily
extrapolate for Bt crops in other parts of the country.
"The pink bollworm is specialized on cotton, while other key pests of Bt
cotton in other parts of the country are generalists that eat other
crops," Rissler said.
Carriere added: "Here in Arizona it is clear Bt cotton has caused a
dramatic reduction in the use of synthetic insecticides. But I'm talking
about Arizona. This is not my general position for every transgenic."