Consuelo De Moraes, an entomologist at the Coastal Plain Experiment Station in Tifton, Ga., inspects a tobacco plant as part of her research into the chemical distress calls plants send out when they are attacked by pests. ASSOCIATED PRESS

Scientist finds plant SOS messages

Web posted January 24, 1999

Associated Press

TIFTON, Ga. -- Like a microscopic 911 call, plants can summon an insect rescue squad when they are attacked by pests, and the signal is specific enough to tell the helpful bugs exactly what to expect when they arrive on the scene.

Scientists have known for years that plants could send out distress calls to wasps and other insect bodyguards, but Department of Agriculture researchers in Tifton say they are just beginning to understand how sophisticated the messages can be.

They hope to find out more about the signals and eventually to use them to develop chemical-free pest control systems.

``We'll always use pesticides,'' said USDA entomologist Joe Lewis, a veteran biological control researcher in Tifton. ``But they should be the backup. Now we're using them as the first line of defense.''

Using beneficial insects to help control pests will save farmers money and be better for the environment, Mr. Lewis added.

``Our growers are going to have to find a better way, doing what nature did before pesticides,'' he said.

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.

The two caterpillars attack numerous crops and cost U.S. farmers about $6 billion a year in lost crops and pesticide expenses.

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.

``This is the first time that somebody proved that plants produce a different response to different caterpillars,'' said Ms. De Moraes, 29, one of a group of USDA scientists working at the Tifton experiment station.

Mr. Lewis called Ms. De Moraes' work a ``benchmark.''

``Her work went another step,'' said Mr. 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.

Without the signal, the wasps can't always find the deceptive caterpillars, who usually move to a new location after eating and toss their feces away to minimize their scent.

Ms. 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.

She then analyzed the chemical compounds using gas chromatography and found they were different for each type of caterpillar.

``It's amazing how evolutionary forces shape the system,'' said Ms. De Moraes, who earned her doctorate at the University of Georgia.