Insect Communication with Pheromones


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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 Woman Being Swarmed by Bees
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
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
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