Insect Communication
with Pheromones
A very important mechanism
which insects use to communicate are pheromones.
Pheromones are simply any chemical released into the environment
for communication purposes. The chemical and physical
properties of pheromones differ greatly depending on their
purposes in communication. This is especially important
given that pheromones are not waves of any kind and therefore must
piggyback on the air currents around them or in other cases stick
to a surface in order to serve their purpose efficiently.
Alarm Signals
The purpose of these signals is to warn fellow species members of
a danger but not to waste time or energy that could be used to eat
or mate. In order to achieve this insects use pheromones
which disperse rapidly into the air and keep dispersing quickly,
this way unless the alarm signal is continuously being released
the insects won't remain in alarm mode.
An important aspect of alarm signals is the insects which receive
them. Insects don't want to over react to a low
concentration of alarm signal pheromone. To avoid this their
sensory organs for these sorts of pheromones require large
concentrations to activate a behavioral response. Insect
behavioral responses include moving toward the areas of higher
concentration so as to gather more workers in that area and remedy
the problem. For an example of this just imagine the
reaction a beehive has to an intruder. Alarm signals
generally do not cause insects more then a few centimeters away to
react, although this is not always the case as in Africanized bees
which have adapted to react more violently to smaller
concentrations of alarm signal pheromones.
Image of a woman being
swarmed by bees
http://www.everythingweird.com/entry/bees-attack/
Sex Pheromones -the
ultimate perfume
While alarm signals generally need large concentrations to illicit
a reaction, sex pheromones are the extreme opposite. These
pheromones emitted by a ready-to-mate female and are designed to
disperse quickly over large distances. As soon as the male
senses sex pheromones in the air he frantically begins a race for
the female, the first male to arrive passes his genes on to the
next generation. Due to this evolutionary pressure males of
many species, especially those of the order Lepidoptera (butterflies
and moths), have developed extremely sensitive sensory
organs in the form of antennae. These antennae increase the
males chances of successfully mating by increasing the detecting
surface area. Faster detection of pheromones could mean a
head start. Some moths such as the male Indian Luna moth are
so sensitive to female pheromones that they can detect a single
sex pheromone molecule over 6 miles away! Some scientists
are looking into designing a similar mechanism to build highly
sensitive gas leak detection devices which could potentially save
lives.
highly plumed antennae
of male moth
http://www.hsu.edu/pictures.aspx?id=11657
But Insects beware
not all sex pheromones are from the females of the same
species. Several species of spiders
emit the female sex pheromone for other insects only to prey on
the unsuspecting and lovestruck males who approach them.
Orchids have also
been known to trick male wasps into "mating" with them by both
looking and smelling like the female of their species.
Unfortunately for the males the only thing the plants give them is
an extra sac of pollen to haul around.
Other uses of
pheromone communication in insects include food-nest trails in
ants (hymenoptera: formicidae) and termites (Isoptera),
reproductive suppression pheromones in female honeybee workers (Hymenoptera:
Apidae), and even dead
pheromones emitted by ants after they die to mark them for removal
from the nest.
In order to disperse insect pheromones have some very important
properties such as polarity (positive or negatively
charged). The charge on the molecules allows insect
pheromones to attract to molecules in the air so that they can be
moved along with the air currents. If the charge is stronger
it disperses faster and vise versa. Other insects use
behavioral mechanisms such as the frequency of pheromone dispersal
and time of dispersal (i.e. release at night when warm air from
the ground is rising) to aid in their effectiveness of
communication.
By understanding the mechanisms and purposes of insect pheromones
and dispersal we can create synthetic pheromones to lure insects
into traps or away from agricultural areas where they could pose a
potential economic problem. Synthetic pheromones also have
the potential to lure rare insects out of the niches to be sampled
more readily. These samplings of rare insects could provide
a tool to easily evaluate the overall ecological health of an
area.
Want to know more? Check out how insects use Light!!!