In this article we will discuss about:- 1. Meaning of Pheromones 2. Types of Pheromones 3. Chemistry.
Meaning of Pheromones:
The term pheromone was introduced by Peter Karlson and Martin Luscher (1959) and is based on the Greek pherein (to transport) and hormon (to stimulate) is a chemical that triggers a natural behavioral response in another member of the same species. There are alarm pheromones, food trail pheromones, sex pheromones, and many others that affect behavior or physiology.
Their use among insects has been particularly well documented, although many vertebrates and plants also communicate using pheromones. Pheromones are chemicals released by an organism into its environment enabling it to communicate with other members of its own species.
Karlson and Martin Luscher proposed the term to describe chemical signals from conspecifics which elicit innate behaviours soon after Butenandt characterized the first such chemical.
Types of Pheromones:
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1. Insect Pheromones:
i. Alarm Pheromones:
Some species release a volatile substance when attacked by a predator that can trigger flight (in aphids) or aggression (in bees) in members of the same species.
When an ant is disturbed, it releases a pheromone that can be detected by other ants several centimeters away. They are attracted by low concentrations of the pheromone and begin to move toward the region of increasing concentration. As they get nearer to their disturbed nestmate, their response changes to one of alarm. The higher concentration causes them to run about as they work to remedy the disturbance.
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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).
ii. Queen Mandibular Pheromone:
Honeybee queens spend their lives literally surrounded by a retinue of worker bees. The workers are attracted to her by a pheromone that she releases from her mandibular glands. The pheromone is a mixture of alcohols and organic acids.
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Among its Effects:
1. Inducing the workers to feed and groom her;
2. Inhibiting the workers from building queen cells and rearing new queens;
3. Inhibiting ovary development in the workers.
iii. Epideictic Pheromones:
These pheromones were deducted in insects. These pheromones are different from territory pheromones. According to Fabre, those females who lay their eggs in these fruits deposit these mysterious substances in the vicinity of their clutch to signal to other females of the same species so that they will clutch elsewhere.
Hundreds of pheromones are known with which one sex (usually the female) of an insect species attracts its mates. Many of these sex attractants – or their close chemical relatives – are available commercially.
They have proved useful weapons against insect pests in two ways:
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a. Male Confusion:
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.
b. Insect Monitoring:
Insect sex attractants are also valuable in monitoring pest populations. By baiting traps with the appropriate pheromone, a build-up of the pest population can be spotted early.
Even if a conventional insecticide is the weapon chosen, its early use reduces:
1. The amount needed
2. Damage to the crop
3. Cost to the grower, and
4. Possible damage to the environment.
Early detection of pest build-up is a key ingredient in the system known as integrated pest management (IPM).
They are produced by one or the other sex, these pheromones attract individuals of both sexes.
These are powerful attractant molecules that some organisms may use to attract mates from a distance of 2 miles or more. This type of pheromone generally elicits rapid response but is quickly degraded. In contrast, a primer pheromone would have a slower onset but a longer duration.
These pheromones trigger a change of developmental events.
vii. Territorial Pheromones:
These pheromones are laid down in the environment and mark the boundaries of an organism’s territory. In dogs, these hormones are present in the urine, which they deposit on landmarks serving to mark the perimeter of the claimed territory.
These pheromones are common in social insects. For example, ants mark their paths with these pheromones, which are non-volatile hydrocarbons.
Some of the ants lay down an initial trail of pheromones as they return to the nest with food. This trail attracts other ants and serves as a guide. As long as the food source remains, the pheromone trail will be continually renewed. The pheromone must be continually renewed because it evaporates quickly. When the supply begins to dwindle, the trail making ceases. In at least one species of ant, trails that no longer lead to food are also marked with a repellent pheromone.
In animals, sex pheromones indicate the availability of the female for breeding. Male animals may also emit pheromones that convey information about their species and genotype. Many insect species release sex pheromones to attract a mate and many lepidopterans can detect a potential mate from as far away as 10 km (6.2 miles).
Pheromones can be used in gametes to trail the opposite sex’s gametes for fertilization. Pheromones are also used in the detection of oestrus in sows. Boar pheromones are sprayed into the sty, and those sows which exhibit sexual arousal are known to be currently available for breeding.
2. Other Pheromones (Unclassified):
This classification, based on the effects on behavior, remains artificial. Pheromones fill many additional functions.
The scientific literature (2005) recognized four classes of pheromones; territorial markers, mother-infant, menstrual synchrony, and the fourth class that is the area of expertise for Dr. Cutier and Athena Institute; human sex-attractant pheromones.
i. Plant Pheromones:
Pheromones also exist in plants: certain plants emit alarm pheromones when grazed upon, resulting in tannin production in neighboring plants. These tannins make the plants less appetizing for the herbivore.
In women during synchronization of menstrual cycles there is an unconscious odor cues (the McClintock effect, named after the primary investigator, Martha McClintock, of the University of Chicago).
The studied proposed that there are two types of pheromone involved:
1. Produced prior to ovulation, shortens the ovarian cycle.
2. Produced just at ovulation, lengthens the cycle. This is analogous to the Whitten effect.
Other studies have suggested that people might be using odor cues associated with the immune system to select mates who are not closely related to themselves. Using a brain imaging technique, Swedish researchers have shown that homosexual and heterosexual males’ brains respond differently to two odors that may be involved in sexual arousal, and that the homosexual men respond in the same way as heterosexual women. It was proposed that there is a possible role for human pheromones in the biological basis of sexual orientation.
Another study shows that the smell of androstadienone, a chemical component of male sweat, maintains higher levels of Cortisol in females. The scientists suggest that the ability of this compound to influence the endocrine balance of the opposite sex makes it a human pheromonal chemosignal.
In 2006 it was shown that a second mouse receptor sub-class is found in the olfactory epithelium. Called the trace amine-associated receptors (TAAR), some are activated by volatile amines found in mouse urine, including one putative mouse pheromone. Orthologous receptors exist in humans providing, the authors propose, evidence for a mechanism of human pheromone detection.
Some body spray advertisers claim that their products contain human sexual pheromones which act as an aphrodisiac. In the 1970’s “capulins” were patented as products which release human pheromones, based on research on rhesus monkeys. Subsequent to that androstenone, axillary sweat, and vomodors have been claimed to act as human pheromones. Despite these claims, no pheromonal substance has ever been demonstrated to directly influence human behavior in a peer reviewed study.
Chemistry:
During the past 40 years, pheromones of hundreds of insect species have been chemically elucidated, including the sex pheromone of the codling moth. Its main component is (E,E)-8,10-dodecadien-l-ol, a primary alcohol containing a straight chain of 12 carbons and two conjugated double bonds. Other moth pheromones are hydrocarbons, epoxides, acetates or aldehydes. These molecules all vaguely resemble fatty acids, from which they are indeed biogenetically derived.
Most pheromones consist of blends of two or more chemicals which need to be emitted at exactly the right proportions to be biologically active. The female effluvia or sex gland can contain additional compounds which are related to the pheromone components and whose biological function is often unclear. On the other hand, many attractants of male moths have been discovered simply by field screening.
In several cases it could later be shown that the attractant found with this technique was identical to the natural pheromone produced by the female. In most others, the composition of the true pheromone is still unknown. You can click the structural formula above to see a list of all the species for which (E,E)-8,10-dodecadien-1-ol has been reported as a pheromone or attractant component.