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Unlocking the Chemistry of Pheromones

by batoujitsu

Pheromones are any chemical signal used to communicate between
the members of a species. The existence of pheromones has been
studied most thoroughly with respect to insects, but more complex
species likely also possess pheromones.

The above diagram, by Peter Fluri, shows a female of the codling
moth, Cydia pomonella, raising her abdomen and protruding her sex
gland. She takes this calling posture for a short period in the
early evening hours.

Codling moth males casting through the apple orchards will
eventually be caught in the plume of a calling female get aroused
and steer upwind until they find her and mate with her. Same way,
many other flies and moths raise their abdomen and release
pheromones in order to attract their respective partner for
mating. These pheromones can spread to a wide area. The male
partners will recognize the pheromones released by their females
and they will reach them.

But what do these pheromones actually contain? What is the size
of it? Well, though our researchers have cracked many nuts, still
there are many questions to be answered. The pheromones released
by each organism are different. And pheromones are released for
different functions at different circumstances also like trail
pheromones, alarm pheromones etc. but yet, a generalized
structure of the pheromones have been revealed by our fellow
scientists.

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During the past 40 years, pheromones of hundreds of insect
species have been chemically elucidated, including the sex
pheromone of the codling moth. Its main component is
(E,E)-8,10-Dodecadien-1-ol, Codlemone, a primary alcohol
containing a straight chain of 12 carbons and two conjugated
double bonds. Other moth pheromones are hydrocarbons, epoxides,
acetates or aldehydes. These molecules all vaguely resemble fatty
acids, from which they are indeed biogenetically derived.

The general size of pheromone molecules can be limited to
about 5 to 20 carbons and a molecular weight between 80 and 300.
This is because below 5 carbons and a molecular weight of 80,
very few kinds of molecules can be manufactured and stored by
glandular tissue. Above 5 carbons and a molecular weight of 80,
the molecular diversity increases rapidly and so does the
olfactory efficiency. Once you get above 20 carbons and a
molecular weight of 300, the diversity becomes so great and the
molecules are so big that they no longer are advantageous. They
are also more expensive to make and transport and are less
volatile. In general, most sex pheromones are larger than other
pheromones. In insects, they have a molecular weight between 200
and 300 and most alarm substances are between 100 and 200.

Most pheromones consist of blends of two or more chemicals
which need to be emitted at exactly the right proportions to be
biologically active. The female effluvia or sex gland can contain
additional compounds which are related to the pheromone
components and whose biological function is often unclear. On the
other hand, many attractants of male moths have been discovered
simply by field screening. In several cases it could later be
shown that the attractant found with this technique was identical
to the natural pheromone produced by the female. In most others,
the composition of the true pheromone is still unknown.

If you want to know more, please visit the <a
href="http://phermonesguide.blogspot.com/">Beginners Guide to
Phermones</a> at http://phermonesguide.blogspot.com

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