Study: Plants Fend Off Predators

WASHINGTON (AP) - Scientists studying a wild tobacco plant growing in the Great Basin desert of southwest Utah said the plant has developed a chemical call for help to protect itself from the five-spotted hawkmoth, its most serious pest.

The hawkmoth lays eggs on the plant and when caterpillars hatch they feed on its leaves.

Ian T. Baldwin, co-author of a study appearing Friday in the journal Science, said the leaf-chewing by the caterpillars prompts the plant to release a plume of chemicals that distant predators can detect.

Predator bugs have the difficult task of finding their favorite prey hidden among many green plants in wide open spaces, Baldwin said. By releasing its chemical signals, he said, the tobacco plant helps predators zero in on their food.

In addition to summoning predators, the chemical signals also discourage a continued attack by the egg-laying moth, the researcher said.

The study showed that when moths detect the chemical alert, they will avoid the plant and lay their eggs elsewhere. In effect, the signal calls for help and scares off further attack, Baldwin said.

``Our study demonstrates that the volatile (airborne chemical) bouquet that is released after attack is very complex,' he said. ``Predators are attracted and egg-laying moths are repelled.'

Baldwin said similar defenses have evolved in the cotton, corn, lima bean, pear, and oil seed plants, among others.

In corn, for instance, a chemical signal summons a wasp that deposits eggs inside armyworms that feed on the corn plant. When the eggs hatch, the wasp larvae consume the armyworms.

Lima beans protect themselves from the spider mite with chemicals that attract predator mites that feed on the pests.

Baldwin said the study suggests that what he calls ``indirect defenses' could be engineered into plants and become more successful at controlling agricultural pests than chemical spraying. He notes that insects can develop a resistance to pesticides, but not against natural predators.

``The use of these indirect defenses ... will likely be a more sustainable pest control strategy,' said Baldwin.

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