Scientists Identify Chemical That Triggers Plant “SOS” Call

An insect chemical that prompts corn seedlings to send out a distress signal has been chemically isolated, identified and artificially reproduced by U.S. Department of Agriculture and cooperating scientists.

The chemical, called volicitin, is secreted in the saliva of beet armyworm caterpillars and other similar pests that feed on crops. The researchers say volicitin causes plants to produce chemical aromas, which in turn lure beneficial insects to attack the crop pests. The finding, published in the May 9 issue of the journal Science, is the latest in an ongoing research effort to find environmentally friendly ways to control crop pests.

In lab studies, scientists with USDA’s Agricultural Research Service extracted volicitin from the saliva of beet armyworms. The researchers then cut corn seedling leaves and dabbed volicitin onto the damaged leaf areas. The researchers found that volicitin induced the seedlings to give off chemical aromas that act like distress signals. The plant chemicals lured a beneficial wasp, Cotesia marginiventris, that attacked the caterpillar pests. Simply damaging the seedling leaves--without adding volicitin--did not induce the same “SOS” response, the scientists said.

ARS has filed a patent application on the volicitin compound. Scientists said the discovery could help plant breeders develop new crop varieties with enhanced chemical defense systems. Plants would be better able to attract beneficial insects that could fend off the attacking pests, cutting down on pest damage and allowing farmers to reduce pesticide applications to control crop pests.

The identification of volicitin is a key finding in understanding the natural defense systems that plants use to defend themselves against insect attack. In the January issue of the journal Nature, the scientists reported for the first time that cotton plants actually synthesize distress-signal chemicals when attacked by pests--and that the chemicals aren’t simply stored inside the plant. They also found that the distress signals emanate from the entire plant--not just from the spot where the pest has fed.

Cooperating on the Science report were scientists with the ARS Center for Medical, Agricultural and Veterinary Entomology Research, the University of Neuchatel in Switzerland, the Virginia Military Institute and Chalmers University of Technology in Sweden.

Scientific contact: James H. Tumlinson, Center for Medical, Agricultural and Veterinary Entomology Research, USDA/ARS, Gainesville, Florida, phone (352) 374-5730, fax (352) 374-5707, jtumlinson@gainesville.usda.ufl.edu.