Plants use scents to ward off pests

Hi all - 

Thought you might find the below information interesting. Read it in
Spectrum  ("The Wholistic News Magazine"), a print magazine that gives
brief summaries of the information in articles from lots of sources, on
topics like food & nutrition, environment, mind & spirit, healing,
medicine, and society. (3519 Hamstead Court, Durham NC 27707, email:
wholenews@msn.com).  This particular piece is based on information in New
Scientist 9/7/96.

Hope you find it interesting - 

P. Dines

Two scents that some people find irresistible, that of pine trees and oil
of wintergren, are so repulsive to some insects that farmers could use them
to protect their crops against insect pests.  In fact, researchers are
discovering that plants themselves commonly use odors to ward off unwanted

When attacked, many plants release smells that not only repel their
attackers, but summon other insects that prey on the pests. For example,
when lima bean plants are attacked by spider mites, they secrete a blend of
volatile chemical that attract predatory mites, which then feast on the
spider mites.

It now appears that some plants time their SOS signals to coincide with the
activity of the predators they wish to attract.  Maize and cotton plants
send signals to parasitic wasps, and these odoriferous message reach their
peak at the time of the day when the easps are most active. The signals
stop at night when the easps become dormant. 

Plznts may even communicate with eac hother using scent signals.
Researchers have found that lima bean plants becoe less attractive to
spider mites and more attractive to predatory wasps after downwind exposure
to plants already infested by the mites. The healthy plants are either
detecting the signals from the infested plants, and turning on their own
defenses, or absorbing the volatile, bug-repelling chemicals released by
their neighbors upwind.

Scientists are attempting to take advantage of the odorous defenses used by
plants to help farers protect their crops from pests. One approach being
explored is the application of the SOS chemicals directly to crops, thereby
attracting more pest predators. Another is breeding into plants the
capability of sending "louder" scent signals.  In a world where $7 billion
is spent on conventional chemical pesticides, the addition of these
nontoxic pest-control methods would be welcome.

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PD NOTE: This approach is better than synthetic pesticides.  But rather
than monkeying around with a system that's working, even better might be to
figure out which plants currently send out stronger/better signals and
recreate those conditions?  (I bet it's the plants that are the best
nourished/healthy.) Then we don't need to recreate nature with a scent
product, which we then have to time (it seems the plants are best at timing
it already), but rather support the plant in sending it out. It'd also be
great to see this type of research on other plants.  In general, it seems
to me we'll get more mileage and less toxics by spending
time/attention/money on understanding the way nature already regulates
itself and learning how to work with that (vs. the synthetic pesticide
model, which allows seeking one goal (getting rid of one pest) to tear
asunder an entire local (and, by extension, global) ecosystem).  There is
much to nature we still don't know - finding out would be to our advantage,
recklessly destroying what we don't understand is not.