- TIFTON, Ga. (AP) - Like a microscopic
911 call, plants can signal an insect rescue squad when they are attacked
by pests. In fact, researchers say, the signal is specific enough to tell
bugs exactly what to expect when they arrive on the scene.
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- Scientists have known for years that
plants could send out distress calls to wasps and other insect bodyguards,
but Department of Agriculture researchers say they are just beginning to
understand how sophisticated the messages can be. They hope to find out
more about the signals and eventually use them to develop chemical-free
pest control systems.
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- "We'll always use pesticides,"
said USDA entomologist Joe Lewis, a veteran biological control researcher.
"But they should be the backup. Now we're using them as the first
line of defense."
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- Using beneficial insects to help control
pests will save farmers money and be better for the environment, Lewis
added.
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- "Our growers are going to have to
find a better way, doing what nature did before pesticides," he said.
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- During three years of research at the
University of Georgia's Coastal Plain Experiment Station in Tifton, entomologist
Consuelo De Moraes showed that cotton, corn and tobacco plants send out
one signal when they're being attacked by corn ear worms and another when
they're being attacked by tobacco bud worms.
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- The two caterpillars attack numerous
crops and cost U.S. farmers about $6 billion a year in lost crops and pesticide
expenses.
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- The plants summon a black, half-inch
parasitic wasp, known as cardiochiles nigriceps, that is a natural enemy
of the caterpillars. The wasp, a species common on Southern farms, lays
an egg in the caterpillar. The egg then becomes a larvae which consumes
the caterpillar. It crawls into the ground, wraps itself in a cocoon and
emerges as a new wasp.
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- "This is the first time that somebody
proved that plants produce a different response to different caterpillars,"
said De Moraes, one of a group of USDA scientists working at the Tifton
experiment station.
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- Lewis called De Moraes' work a "benchmark."
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- "Her work went another step,"
said Lewis, who has been studying biological pest controls for at least
20 years. "Not only are they sending out a cue, they are saying, 'Here's
where it is and here's what it is."' The plants also sweeten the deal
by producing nectar to feed the wasps, giving them an incentive to stay.
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- Without the signal, the wasps can't always
find the deceptive caterpillars, who usually move to a new location after
eating and discard their feces to minimize their scent.
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- De Moraes was doing routine work in 1996
as a graduate student when she noticed wasps congregating on plants that
were being attacked, but not on plants that were free of the caterpillars.
Through a series of tests, she proved that the wasps were responding to
chemical signals emitted by the plants.
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- She then analyzed the chemical compounds
using gas chromatography and found they were different for each type of
caterpillar.
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- "It's amazing how evolutionary forces
shape the system," said De Moraes, a native of Brazil who earned her
doctorate at the University of Georgia and published her results in the
journal Nature last year.
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- Rick Karban, an entomologist at the University
of California-Davis, said De Moraes' work shows how specific the plants'
distress signals can be. Karban studies the physical responses of plants
to pest attacks. He's shown that some develop a tougher skin, some become
less tasty and some produce chemicals that are harmful to the pests.
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- "In nature, there are natural ways
to keep the pests in check," he said. "Their work helps us understand
how it happens. It can be a real advance in terms of taking advantage or
manipulating those responses to our benefit."
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