Pheromones: Chemistry, Structure and Functions

The first pheromone was identified in 1953. This pheromone, called BOMBYKOL is secreted by female moths and carried a “come to me” signal to males. This signal can travel large distances and is effective at low concentrations.

The mammalian pheromone system was more difficult to understand because mammals, far from having the simple stereotyped behaviour of insects, have complex and independent behaviour. Mammals were found to detect pheromones through an organ in the nose called the VNO, which is similar in function to the olfactory membranes but connects to the hypothalamus.

Scientists were beginning to speculate whether a pheromone system existed in humans. In the 70’s Martha McClintock noticed that females living in close proximity underwent a changing of phase of their menstrual cycles causing them to ovulate at similar times.

It was discovered that this effect was due to a chemo signal, or pheromone. In 1974 Dr George Dodd discovered the first human sex pheromone, alpha-androstenol.

Although humans are mammals, it is not certain that all pheromones are detected by the human VNO; some may be detected by the olfactory membranes (by normal smelling). It is known that pheromones do not need to actually be smelled to exert their subconscious effect, although human pheromones that are commercially available do have a detectable scent at high concentrations.

However, not all people are actually able to detect the conscious odour of pheromones, but apparently this does not reduce their subconscious effect.

Although commercially available human pheromones address a quite specific area of human interaction, attraction, pheromones play a role in other areas such as mother-infant bonding. Pheromone products are also from a specific family of pheromones which are derived from sex hormones which indicate youth, fertility, etc.

Everybody secretes these chemicals, but not in the same quantities. Other pheromones are unique to the individual, such as the pheromones that signal tissue type (Major Histo-compatibility – the “T-shirt study”).

The hormone derived pheromones are naturally secreted onto the skin via the apocrine glands, which are primarily situated in the arm pits and the pubic region; the hair in these areas helps to disperse the pheromones effectively.

These scent glands have in some cases evolved to perform an entirely different and specialised role, for example in the ear to produce ear wax, or in women’s breasts to produce milk.

It is known that androstenol can induce a spike in Luteinizing Hormone in both sexes, and this leads to a spike in testosterone levels which may be responsible for feelings of attraction.

Definition of Pheromones

A pheromone (from Greek phero “to bear” + hormone from Greek – “impetus”) is a secreted or excreted chemical factor that triggers a social response in members of the same species.

Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual.(5)

Another definition of pheromones

Pheromones are naturally occurring substances the fertile body excretes externally, conveying airborne messages that can generate social responses from others of the same e species

Pheromones were first defined by biologists in 1959 as chemical substances that can be excreted by the animals to trigger the reproductive behavioural response from a recipient of the same species.

Pheromones are now widely recognized to be the mediator that promotes the survival of each species.(6)

TYPES OF PHEROMONES

1. Aggregation pheromones
2. Alarm pheromones
3. Epideictic pheromones
4. Releaser pheromones
5. Primer pheromones
6. Signal pheromones
7. Territorial pheromones
8. Trail pheromones
9. Information pheromones

1. Aggregation pheromones

Its functions in the defense against predators, mate selection, and overcoming host resistance by mass attack. A group of individuals at one location are referred as aggregation, whether consisting of one sex or both sexes.

Male-produced sex attractant have been called aggregation pheromones, because they usually result in the arrival of both sexes at a calling site and increase in density of conspecifics surrounding of the pheromone source. (7)

Most sex pheromones are produced by the females and small percentage of sex attractants are produced by males

2. Alarm pheromones

Some species that releases a volatile substance, when attacked by a predator that can trigger flight or aggression in ants, insects are the members of the same species.

Pheromones also exist in plants: certain plants emit alarm pheromones when grazed upon, resulting in tannin production in the neighboring plants. These tannins make the plants less appetizing for the herbivores. (8)

3. Epideictic pheromones

Epideictic pheromones are somewhat different from territory pheromones, when it comes to insects.

Fabre observed and noted how “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 they should clutch elsewhere.(9)

4. Signal pheromones

Signal pheromones that can cause short term changes; such as, the neurotransmitter release which activates a response.For instance, GnRH molecule functions as a neurotransmitter in rats to elicit lordosis behavior. (10)

5. Primer pheromones

Primer pheromones trigger a change of developmental events

6. Trail pheromones

Trail pheromones are common in social insects. For example, ants mark their paths with these pheromones, which are volatile hydrocarbons.

Certain 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.(11)

7. Territorial pheromones

Laid down in the environment, territorial pheromones mark the boundaries of an organism’s territory.

In cats and dogs, these hormones are present in the urine, which they deposit on landmarks serving to mark the perimeter of the claimed territory.

In social seabirds, the preen described as ‘displacement activity’.(13)

8. Information pheromones

Information pheromones are indicative of an animal’s identity or territory. For example, dogs and cats deposit chemicals in and around their territory, which then serve as an indicator for other members of the species about the presence of the occupant in that territory.(14)

9. Sex pheromones

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 .(15)

STRUCTURES OF PHEROMONES

Some of the structures of the pheromones are given below

1. 4-heptanone

2. 2-methyl 4-heptanone

3. 6-methyl 5-heptene- 2- one

4. 4 -hydroxy 4-methyl-2-pentanone

Facts about Pheromones

The general size of pheromone molecules can be limited to about 5 to 20 carbons and a molecular weight between 80 and 300. This is because below 5 carbons and a molecular weight of 80, very few kinds of molecules can be manufactured and stored by glandular tissue.

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Above 5 carbons and a molecular weight of 80, the molecular diversity increases rapidly and so does the olfactory efficiency. Once we get above 20 carbons and a molecular weight of 300, the diversity becomes so great and the molecules are so big that they no longer are advantageous.

Those pheromones are also more expensive to make and transport and are less volatile. In general, the most sex pheromones are larger than other pheromones.

But it is the insects, they have a molecular weight between 200 and 300 and most alarm substances are between 100 and 200.

Pheromones, like the visual communication, use single, individual messages as well as composite chemical messages.

For example, in many insects and mammals, each endocrine gland produces a pheromone with a different meaning. However, many times pheromones from different glands are secreted at that same time.

Female wasps release attractant pheromones from their head and sexual excitant pheromones from their abdomen at the same time. This can increase the effectiveness of the message or create an entirely new message.

It is also possible for different substances with different meanings to be generated in the same gland. (19)

Dr. Winnifred culter -co-discoverers of human Pheromones(1986)

Dr. Cutler’s research established proof that human pheromones affect relationships between men and women. Several years later, in 1993, she took human pheromones one step further. Dr. Cutler developed and marketed a synthetic pheromone known as Athena Pheromone 10:13.

The pheromone is a copy of one given off by “sexually attractive” women in their twenties and it is a colourless, odourless liquid women can wear to attract men. The pheromone proved to be successful and Dr. Cutler and the Athena Institute marketed more synthetic pheromones, including Athena Pheromone 10X for men.

Development of Synthetic Pheromones

The development of other synthetic pheromones, such as those used for pest control, is growing at an extremely rapid rate. The chemical compositions of insect pheromones are very well understood and scientists have been able to produce synthetic pheromones with the same chemical structure.

Simple changes to the structures, such as adding a double bond, conjugation, cyclic rings, or changing the positions of the atoms can completely change the pheromone into a new pheromone. That is what leads to the E and Z pheromones and the differences between dienes and trienes, etc. Other pheromones include nitrogen in their structure, making them amides. (20)

Some of the pheromones example with the structures (21)

Use of Synthetic Pheromones

One popular use of synthetic pheromones is for pest management. Scientists use methods such as pest monitoring, mass trapping, lure and kill, and mating disruption to determine valuable information about pests, the dangers they pose to crops, and how to solve the pest problem.

Pest monitoring is used to determine the purpose for which a certain system of pest removal is to be used. Some factors that are considered in these decisions include scientific factors and commercial factors.

Other important components of monitoring systems include the attractant source, the trap and where to place it, and sufficient knowledge of the pest biology to interpret the catches.

The attractant source is made up of the active ingredient and its controlled release device. The trap design is just the basic structure of the trap itself and it includes designs such as sticky plates, tent traps, wing traps, funnel traps, and milk carton traps.

Mass trapping involves placing a high density of traps in the crop to be protected to remove a high proportion of individuals from the population.

However, lack of attraction of females to the attractant source, lack of efficient traps, high insect populations and trap saturation, and a need for high density traps per unit of surface area (aka cost) make mass trapping difficult.

It is commonly used on fruit flies, moths, and beetles.

Lure and kill techniques are very similar to mass trapping, except once the insect is attracted to the semi chemical lure, it is subjected to a killing or sterilizing agent instead of being trapped. It is also known as attracticide and attraction-annihilation. Lure and kill consists of two components, the lure and the affector. The lure consists of odours, visual cues, or both and the affector eliminates the insect from the population. Below is a table of some common lures and and affectors used. Lure and kill uses target devices, including physical traps and sprayable formulations, which use pheromones that are released from planes and are slowly released. It is mainly used on fruit flies, house flies, and tsetse flies.)

Mating disruption is the use of pheromones to try and minimize or prevent egg laying by females. This is done by interfering with the mating behaviour processes between males and females. Controlled release chemicals are used before the onset of pest activity and they are released in small amounts for weeks or months. This strategy has become so successful that it is now used in agriculture, horticulture, and forestry.

The three major strategies of mating disruption are confusion, trail-masking, and false-trail following. Confusion is caused by the constant exposure of males to a high concentration of pheromone fog, which causes adaptation of the antennal receptors and habituation of the central nervous system. This prevents the male from responding to normal levels of the pheromone released by females.

Trail-masking is using a synthetic pheromone to destroy the pheromone trail layed by the females. False-trail following is laying numerous spots of synthetic pheromone in high concentrations to present the insect with many false trails to follow. It is dependent mainly upon the number and intensity of the pheromone dispensers.

It took many years to develop environmentally safe controls that did not have severe effects on other species, but scientists have now achieved relatively successful and specific chemicals. Mating disruption is used for insect pests of cotton, rice, forest insects, and fruit and vegetable pests.

Advantages of Pheromones (22)

There are many advantages to using chemical signals.

Some basic ones include the fact that chemicals can transmit through darkness, around obstacles, and they are very energetically efficient. Pheromones are relatively cheap to biosynthesize and they can be released in a very simple manner, including the simple operation of opening a gland.

Pheromones can also last for days and be transmitted over great potential distances. This includes millimetres for microorganisms and kilometres for other organisms, without even altering the reception or biosynthesis. Some pheromones last so long that once they are released, they are actually used by the same organism in the future if it returns.

Some pheromones are not very specific and will effect other species when they are released. For example, agitated honeybee workers discharge isoamyl acetate or 2-heptanone, which alarms the other nestmates but also alarms any ants or termites that are in the vicinity. This is beneficial to the ants termites, who are now aware of the danger that may be present. (22)

Disadvantages of Pheromones (22)

There is one major disadvantage of chemical communication.

It is very slow. Organisms cannot quickly transmit pheromones over long distances or change from one chemical message to another. Also, there has been no evidence that organisms use amplitude and frequency modulation in the transfer of pheromones.

Although slow transfer is a major disadvantage, organisms have been able to adapt to counteract it. They do this by the multiplication of glands and other principal biosynthetic sites to allow the independent discharge of pheromones with different meanings. One example of this is the black-tailed deer.

The deer produces pheromones in at least seven different sites, including urine, feces tarsal glands, metatarsal glands, preorbital glands, forehead glands, and interdigital glands. The pheromones from each site have a different function.

Comparison of Synthetic and Natural Pheromones (23)

Many times, synthetic pheromones that are used in pest control, insect monitoring, etc. are successful, as mentioned in the “use of synthetic pheromones” section. Scientists can actually trick insects into thinking the synthetic pheromones are actually natural pheromones released by other insects.

Therefore, there is not much debate about whether or not synthetic pheromones used for insect control are effective and similar to natural insect pheromones.

The controversial comparison is between human pheromones and the synthetic human pheromones, now being produced and added to colognes, perfumes, etc.

The pheromones that are located in the perfumes are actually androstenone and androstenal, or known to critics as “pig pheromones”.

Figure taken from http://www.erox.com/SixthSense/StoryOne.html

Literature Review

FACTS OF PHEROMONES

The Washington Post , 11/18/86.

Pheromones Discovered in Humans(24)Newspaper.

by Boyce Rensberger

‘Scientists in Philadelphia have established for the first time that the human body produces pheromones, special aromatic chemical compounds discharged by one individual that affect the sexual physiology of another.

Although animals have long been known to secrete pheromones, which typically function as sex attractants, and although the existence of such chemicals in humans has long been speculated, the new research is the first to establish their existence in humans’

USA Today, 11/19/86

The Real Chemical Reaction between the Sexes (25)

USA Today

by Kim Painter

Chemicals in men’s bodies can cause their female sex partners to be more fertile, have more regular menstrual cycles and milder menopause, landmark research shows.

And women who have sex with men at least once a week benefit most from the chemicals, which apparently work through the sense of smell.

“The exciting part is the effect we have on each other. Men are important to women,” says Dr. Winnifred B. Cutler of Philadelphia, whose studies show for the first time that chemicals called pheromones exist in humans.

Pheromones have long been known to exist in animals, as scents that attract sex partners. Cutler’s new studies…show women are affected by pheromones from men and women:

*Women exposed to another woman’s “female essence” menstruated at the same time after a few months, confirming a long-observed phenomenon that women who live together menstruate at the same time.

Cutler’s other studies show women who have sex with men at least once a week have regular menstrual cycles and fewer fertility and menopause problems, apparently because of exposure to pheromones.

CNN Online, and WebMD.com article, 6/25/99

Pheromones: Potential participants in your sex life(26)

By Deb Levine

Copyright WebMD.com

In 1986 Dr. Winifred Cutler, a biologist and behavioural endocrinologist, co discovered pheromones in our underarms.

She and her team of researchers found that once any overbearing underarm sweat was removed, what remained were the odourless materials containing the pheromones.

Dr. Cutler’s original studies in the ’70s showed that women who have regular sex with men have more regular menstrual cycles than women who have sporadic sex.

Regular sex delayed the decline of estrogens and made women more fertile. This led the research team to look for what the man was providing in the equation.

Conclusion

As you can see, pheromones are a much bigger part of our lives than form of chemical communication between organisms.

There have been significant increases in the knowledge humans have about pheromones in the past several decades, but there is still plenty of information we do not know about them.

For example, we might know the chemical structure of human pheromones, but we have yet to determine whether or not the VNO plays a role in their function or if the VNO is even functional.

The study of insect pheromones has set the foundation for the study of pheromones as a whole and in recent years we have been taking it a step further, to the human pheromone level.

As always, technology has allowed us to do more and more experiments and acquire more and more knowledge about pheromones.

Some of the results of recent studies are astonishing; just take a look at the article by Dr. Gallup that will be released in June 2002. If the rapid increases in experimentation and knowledge continue, soon we might be able to control other people’s actions, just like we control insects, by simply spraying a chemical.(27)