CATERPILLARS BEWARE, THE PLANTS ARE FIGHTING BACK Tuesday November 10 7:17 AM ET

WASHINGTON (Reuters) - Caterpillars munching on corn may inadvertently contribute to their own demise by helping the plants summon aid, researchers said Monday.

Plants are known to send out chemical signals when they are under attack by insects and animals. Such signals may help other plants put up chemical defenses, or may attract predators that eat the insects.

For example, acacia trees are known to send out a chemical signal when animals eat their leaves that stimulates neighboring acacias to produce a foul-tasting chemical.

And corn, when being chewed on by beet armyworm caterpillars, is known to send out chemicals that attract parasitic wasps that attack the caterpillars.

But how does the corn make such a specific plea for a predator that likes beet armyworm caterpillars?

James Tumlinson and colleagues at the U.S. Department of Agriculture Center for Veterinary Entomology in Gainesville, Florida, found that the caterpillars set off a chemical change that helps the corn identify them.

Writing in the Proceedings of the National Academy of Sciences, Tumlinson's team said they discovered the caterpillars get a chemical known as linolenic acid from the corn.

Their bodies metabolize this into another chemical that gets back onto the plant as the caterpillar chews and, essentially, drools.

This may be the ``signature'' molecule that allows the plants to tell which bug is eating them. The corn can then send out the signal for the right predator -- in this case, a wasp that attacks the caterpillar, the researchers wrote.