Definition of pheromones. Pheromones are chemicals produced as messengers that affect the behavior of other individuals of insects or other animals. They are usually wind borne but may be placed on soil, vegetation or various items. Tom Eisner, a foremost authority in the science of chemical use by insects, claims that each species of insect relies on some one hundred chemicals in its life, to engage in such routine activities as finding food and mates, aggregating to take advantage of food resources, protecting sites of oviposition, and escaping predation. It has been found that pheromones may convey different signals when presented in combinations or concentrations. Pheromones differ from sight or sound signals in a number of ways. They travel slowly, do not fade quickly, and are effective over a long range. Sound and sight receptors are not needed for pheromone detection, and pheromone direction is not limited to straight lines.
Examples of pheromone use by insects and spiders. Pheromones have long been known to be important to the lives of insects in mating, as witnessed, for example, in some of the larger silkworm family moths, where males are noted to travel nearly 30 miles to a female, following a pheromone trail in the air. Male Cecropia moths are estimated to detect and respond to a few hundred molecules of pheromone in a cubic centimeter of air. In Honeybee colonies, the queens secrete a glandular substance (a pheromone) that is passed among worker castes, and this secretion coordinates nearly all activities of the workers. One control is the non-development of the ovaries of the workers. The normal effect of a sex pheromone is to attract male mealworm beetles to the female, but it has been found that the first male to mate with the female then covers her with another pheromone, an anti-aphrodisiac, which dissuades other males from mating with her. This strategy may conserve the energy of the female or have other benefits. Some tiny parasitic wasps are known to have evolved to recognize and follow the sex-attractant pheromones of the hosts that they parasitize or of the prey that they eat. These wasps come from afar, attracted by the pheromones of scale insects, and lay their eggs in the bodies of the scale insects. There, the wasp larvae feed and grow as parasites. Some male cockroaches and crickets produce a pheromone called seducin from their bodies, on which the females nibble during copulation. This pheromone is an aphrodisiac. In 1987, Mark K. Stowe of Harvard University and his colleagues reported that bolas spiders manufacture and release pheromones that are identical to the sex attractant pheromones of females of certain night-flying moths. Thus, male moths following the pheromone in the air for some distance find a spider waiting for them instead of a female moth.
Pheromone use for insect control. The use of pheromones to control phases of the lives of pest species is one method of pest management. Beet army-worms are a serious pest in cotton-producing areas of the United States, causing multi-million dollar losses in 1995 in Texas alone. In 1997, researchers reported success in disrupting mating procedures between male and female Beet army-worms by flooding 35-acre cotton field plots with sex attractant pheromones. With such a pervasion of female scent, the males could not find females for more than 100 days. Certain pheromone traps have been developed and are in common usage by homeowners. Indian Meal Moths (Pantry Moths) are attracted to a pheromone in a small box lined with a sticky substance and are thus captured for disposal.
Selected References:
Happ, G. M. 1969. "Multiple sex pheromones of the mealworm beetle, Tenebrio Molitor Linnaeus." Nature, volume 222: 80-181.
Metcalf, R. L. and Metcalf, R. A. 1994. Attractants, repellents, and genetic control in pest management. In R. L. Metcalf and W. H. Luckmann, Introduction to Insect Pest Management, 3rd edition. John Wiley and Sons, New York.
Prestwich, G. D. and Blomquist, G. J., editors. 1987. Pheromone Biochemistry. Academic Press, New York.
Shorey, H. H. and McKelvey, J. J. 1977. Chemical Control of Insect Behavior. Wiley-Interscience, New York.
Stowe, M. K., Tumlinson, J. H., and Heath, R. R. 1987. "Chemical mimicry: bolas spiders emit components of moth prey species sex pheromones." Science, Volume 236: 964-967.
Thornhill, R. 1983. The Evolution of Insect Mating Systems. Harvard University Press, Cambridge, Massachusetts.
