By Sharon Durham
A new class of compounds has been discovered that should help shed
more light on how plants respond to insect attacks. Agricultural Research
Service (ARS) scientists with the Center for Medical, Agricultural and
Veterinary Entomology (CMAVE) in Gainesville, Fla., along with colleagues at
the Virginia Military Institute and the Pennsylvania State University,
isolated the compounds from oral secretions of Schistocerca americana
grasshoppers fed corn seedlings.
Plants, and the insects that feed on them, engage in a relationship
involving many resultant hormonal and chemical changes in the plant,
including induced production and emission of volatile organic compounds, or
VOCs. These physiological changes, brought about by a group of compounds
known as elicitors, vary?not only for different plants, but also with the
insect species feeding on a plant. Understanding the plant- insect
interaction is important in crop science and insect pest management.

ARS chemist Hans T. Alborn, in CMAVE's Chemistry Research Unit, led
the team that isolated the previously unidentified class of compounds. They
named them caeliferins because preliminary analyses of oral secretions
collected from several species of Orthoptera (grasshoppers, katydids and
crickets) indicated that the compounds may be present in most, if not all,
grasshoppers?members of the suborder Caelifera?but not in crickets or
katydids in the suborder Ensifera.

The caeliferins that Alborn isolated have some unique properties, so
they should provide new biological tools and directions for exploring the
physiological ecology of, and interactions between, insects and plants.
Interestingly, the pattern of caeliferins may determine whether S. americana
grasshoppers are solitary or gregarious. If so, the compounds may be found
to influence swarming behavior of locusts.

The CMAVE scientists study elicitors of plant volatile releases to
find ways to induce defensive responses to help crop plants under insect
attack remain healthy and vigorous. It?s well known that insect chewing may
induce release of plant VOCs that summon natural enemies of the attacking
insects. But insects? oral secretions may also provoke direct plant defenses
that impair the pests? performance.


[www.ars.usda.gov]