Pheromones

Pheromones are volatile chemical compounds secreted by insects and animals. They act as chemical signals between individuals influencing physiology and behavior in a manner similar to hormones. Pheromones are important to a variety of behaviors including mate attraction, territorality, trail marking, danger alarms, and social recognition and regulation.

The term pheromone is derived from the Greek words pheran (to transfer) and horman (to excite). In animals, they are produced in special glands and are released through body fluids, including saliva and perspiration. Most pheromones are biogenetically derived blends of two or more chemicals that must be emitted in exact proportions to be biologically active.

There is a remarkable diversity in the stereochemistry of pheromones. Insects are sensitive to and utilize chirality to sharpen the perception of pheromone messages. The configurations of pheromones are critical. Stereoisomers of pheromones, for example, can also be inhibitors of the pheromone action.

Pheromones are found throughout the insect world. They are active in minute amounts. In fact, the pheromones released by some female insects (e.g., Silkworm Moth) are recognized by the male of the species as far as a mile away. The pheromone secreted by the female gypsy moth can be detected by the male in concentrations as low as one molecule of pheromone in 1x1O^I7 molecules of air. Insects detect pheromones with specialized chemosensory organs.

At close range, pheromones continue to be released dictating specific behaviors. Another common example of pheromones in action is the trailing behavior of ants. Scout ants release pheromones that guide other ants to the location of food. In boars, pheromones found in boar saliva are known to cause the female to assume a mating position.

An increasingly important use of pheromones involves the control of insects. Because insects rely on phermomones, these compounds have been used by farmers as a method to control harmful insects. Using insect sex attractant pheromones, scientists have been able to produce highly specific traps and insecticides.

Pheromone traps are used to control the insects such as the European corn borer that damages millions of dollars of crops each year. The European corn borer larvae feed on and bore into the corn plant. Cavities produced by borers reduce the strength of the corn and interfere with plant physiology, including the translocation of water and nutrients. European corn borer pheromone traps contain a substance that mimics (i.e., acts like) a part of the chemical communication system used by female moths when they are are receptive to mating. Male moths are attracted to and captured by the pheromone trap that is coated with a sticky substance that retains attracted insects.

Research continues on insect pheromones. It is assumed that these compounds hold the key to developing insecticides that can kill only harmful insects while being harmless to humans and beneficial insects.

The search for human aphrodisiacs (stimulants to sexual response) is as old as human history. Although the scientific evidence with regard to human pheromones is contradictory and highly debatable, pheromones are often used as an olfactory aphrodisiac in fragrances and perfumes.

The first discovery related to human pheromones was reported the early 1970s. At this time low molecular weight aliphatic acids, called copulins, were found in the vaginal secretion of women. At the time, it was believed that these compounds could stimulate male sexual response. They were thought to work as did their chemical counterparts excreted by monkeys, baboons, and chimpanzees. In the late 1970s, more alleged human pheromones were discovered in human perspiration and urine. Some studies suggest a role for pheromones in the regulation and synchronization of the human female menstrual cycle.

The organ responsible for detecting pheromones in animals is a chemosensory structure in the nose called the vomeronasal organ (VNO). In lower animals, this organ detects substances that mediate sexual and territorial behaviors in species. It was once generally believed that humans did not have a VNO. Embryological texts asserted that this organ disappeared during embryonic development. In the 1980s, however, investigations refuted this alleged disappearance. Subsequent research suggested that a functioning VNO was present in near two small holes on the hard divider in the nose. A group of cells similar to nerve cells are located behind these holes. These cells, which make up the VNO, transmit a signal to the hypothalamus in the brain. The stimulating effect on the hypothalamus results in the production of proteins that may influence behavior.