Scientists Identify Chemical
That Triggers Plant SOS Call
By Sean Adams
May 8, 1997
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 USDAs
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
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 arent 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, firstname.lastname@example.org.