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Pheromones are chemicals released by an organism into its environment enabling it to communicate with other members of its own species.
Unless additional amounts of the alarm pheromone are released, it soon dissipates. This ensures that once the emergency is over, the ants return quietly to their former occupations.
Honeybees also have an alarm pheromone (which is a good thing not to elicit around a colony of "Africanized" bees).
A stick treated with the trail pheromone of an ant (left) can be used to make an artificial trail which is followed closely by other ants emerging from their nest (right). The trail will not be maintained by other ants unless food is placed at its end. (Photos courtesy of Sol Mednick and Scientific American).
Distributing a sex attractant throughout an area masks the insect's own attractant and thus may prevent the sexes getting together. This "communication disruption" has been used successfully against a wide variety of important pests. For example, the sex attractant of the cotton boll weevil has reduced the need for conventional chemical insecticides by more than half in some cotton-growing areas.
The photo (courtesy of USDA) shows the feathery antennae of a male gypsy moth. These detect the pheromone released by the females (who do not fly). In some insects, a single molecule of sex attractant is enough to elicit a response.
Studies of one species of spider, Mastophora cornigera, show that it releases a mixture of volatile compounds that mimic the sex pheromone of the moth species it preys upon. Male moths flying upwind in search of a female end up eaten instead!
A number of species of orchids — each pollinated by the males of a single species of insect (wasps or bees) — emit the same pheromone that is the sex attractant by which females of the insect species attract the males for mating.
Many mammals (e.g., dogs and cats) deposit chemicals in and/or around their "territory". As these vaporize, they signal to other members of the species of the presence of the occupant of the territory.
Domestic rabbit mothers release a mammary pheromone that triggers immediate nursing behavior by their babies (pups). A good thing, too, as mothers devote only 5–7 minutes a day to feeding their pups so they had better be quick about it.
Many animals, including mammals, signal with alarm pheromones. Although neither the source nor the chemical nature of alarm pheromones are known in any mammal, stressed animals release something that triggers quick behavior (e.g., flight or fight) in other members of their species. The pheromone is detected in a special cluster of cells located at the very tip of the nose and thus in a position to detected airborne molecules even before the vomeronasal organ (next paragraph) or nasal epithelium can. The detectors on these cells are primary cilia.
Rats and mice give off pheromones that elicit mating behavior. However, the response is not immediate as it is in the releaser pheromones of mother rabbits and insects. Instead, detection of the pheromone primes the endocrine system of the recipient to make the changes, e.g., ovulation, needed for successful mating.
Primer pheromones are detected by the olfactory epithelium with which normal odors are detected and also in most mammals (but not humans) by the vomeronasal organ (VNO). The VNO is a patch of receptor tissue in the nasal cavity distinct from the olfactory epithelium. The receptors are G-protein-coupled transmembrane proteins similar to those that mediate olfaction, but encoded by entirely different genes.
|Link to discussion of olfaction in mammals.|
The neurons leading from the VNO take a separate path into and through the brain.
It has long been noticed that women living close together (e.g., college roommates) develop synchronous menstrual cycles.This is thought to be because they release two (as yet uncharacterized) primer pheromones
Both pheromones are released from the armpits.
The pheromones are not detected consciously as odors, but presumably trigger the hormonal changes that mediate the menstrual cycle.