What Are The Definitions And Roles Of Pheromones Biology Essay

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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. The definition of pheromone can also be (noun) a chemical substance that is produced by an animal and serves especially as a stimulus to other individuals of the same species for one or more behavioral responses. Simply put, the definition of pheromone is a chemical that alerts you to your surroundings.

Pheromone comes from the Greek word "phero", which means to carry and "-mone", which is short for hormone. So if you look at the definition of pheromone from an etymological perspective, it means a hormone that carries. What does it carry? These can be some type of signals what they carry from one organism to others or from the surroundings. For animals, insects especially, it serves as the means of finding food and alerting them about danger. This is why insect pheromones of pest species, such as the Japanese beetle and the gypsy moth, can be used to trap them or to create confusion so that the pests do not lay eggs on crops. . http://www.pheromones-i.com/definition-of-pheromone.html


In late 1950s, scientists clipped thousands of genitalia from silkworm moth, Bombyx mori, in order to extract its pheromones. Since this time more than one thousand pheromones have been identified by the scientists worldwide. Many more will surely follow in years to come.

These are the chemical messengers used by the insects in order to communicate and are very much similar to the hormones inside the human body. Originally they were known as ecto-hormones or messengers outside the body of the organism. In the year 1959, two German scientists suggested in one of the article in Nature that the name pheromone be coined. This word comes from two Greek words: homan, to carry, and pherin, to excite.

Nearly everyone of us has stopped at one time in order to observe ants as they follow each other along an organized trail they form. On finding a food source, ants lay down a trail pheromone by using their abdomen. Fellow workers of the ants are lured by this pheromone to the trail that leads to the food source. Ants also use other pheromones to their advantage, which includes the defense pheromone released by fire ants to come to the defense of their colony.


Nature has done its own analysis of the pheromones. Semi-chemicals are present in our nature in very primitive, as well as magnificently sophisticated, displays of efficient use of energy and resources. The Bolas spider, Mastophora spp., was reported to attract the male pyralid moths to its unique capturing device with the use of two different self-made pheromones.

Long before entomologists even had learned to use pheromones the Bolas spider was patiently attracting its next meal with a moth sex attractant pheromone. Bolas spiders attract certain male moths by aggressive chemical mimicry of those moth species' sex pheromones. This unique hunting spider is commonly found throughout United States. They spin a line, weight it with a sticky drop of liquid silk (the bolas), and hurl it at their prey, much as the gauche throws his bolas or the angler casts his line.

. http://www.insectslimited.com/66%20History%20of%20Pheromones%20Article.htm













Alarm Pheromone

Whenever an ant is disturbed, it releases a pheromone that can be detected by the other ants several centimeters away. Hence they are attracted by the low concentrations of the pheromone and begin to move towards the region of increasing concentrations. As they get nearer to their disturbed nest mate , their response changes to one of alarm. The higher concentration causes them to run about as they work to remedy the disturbance.

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).

Trail Pheromone

Certain ants as they return to nest with food, lay down a trail pheromone. This trail attracts and guides the other ants to the food. It is continually renewed as long as the food holds out. When the supply begins to dwindle, trail making ceases. The trail pheromone evaporates quickly so other ants stop coming to the site and are not confused by the old trails when food is found elsewhere. And at least in one species of ant, trails that no longer lead to food are also marked with a repellant pheromone.

A stick treated with the trail pheromone of an ant (left) can be used to make an artificial trail with 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.

Releaser Pheromones

Many mammals e.g., dogs and cats deposit chemicals in and 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 . 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 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 nasa epithelium can. The detectors on these cells are primary cilia

Primer Pheromones

Rats and mice give off the 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 trans membrane proteins similar to those that mediate olfaction, but encoded by entirely different genes


Third generation controller : pheromones

Chemicals released externally by insects and which elicit immediate behavioural responses from members of the same species are called pheromones. These compound messengers do not exert toxic effect with in a species, and as such cannot be known as pesticides. However , it has been demonstrated that interference with natural communication mechanisms can provide effective population control of pest species.

Among the many types of pheromones, sex attractants received the greatest attraction. Pheromones are released by one sex of the species (usually the female) to attract the opposite species for the purpose of mating. Other types of pheromones are involved in aggregation and colonization of a host(population attractants), egg laying, and foraging and maintenance of a social order in colonies of insects such as bees and ants.

The insects usually detect pheromones by sweeping the air with their antennae which posses thousands of olfactory hairs. These hairs contain sensory nerve cells which have receptor sites for the chemicals. The presence of a sufficient number of molecules at their receptors leads to depolarization of the membrane of the sensory cell and this generates a nerve impulse which is transmitted to the central nervous system, the greater to number of molecules arriving at the receptor ,to greater is the frequency of impulses transmitted. It has been shown that a sensory cell will respond to one molecule of pheromone and it has been estimated that the presence of some two hundred molecules is sufficient to reduce a behavioural. Thus three hundred grams of a pheromone with molar mass 300 , will kill the following number of the insects,

6*10raise to power 23 molecules are present in 300 gram

200 molecules will be present in(300*200)/6*10raise to power 23

Or , number of insects which will change behaviour by 300 gram of it = 6*10 raise to power 23/300*200= 1*10 raise to power 21 , insects.

Isolation of sex pheromones:

Pheromones are present in trace amounts in insects so that special techniques couples with considerable skill, ingenuity and intuition are required to decipher the structures of these compounds. For example only 500 ug of pure male attractant was isolated from 75000 virgin females full armyworm moths. Obviously the usual techniques of organic chemistry cannot be used for structure analysis of these pheromones a sensitive bioassay is required , which is usually based on the observation of the response of the insect to the pheromone. A common technique is to allow the effluent from a gas chromatograph to pass through a cage containing the insects. Compounds are present in too small an amount to be detected by the detectors in the gas.


These can be detected by the insects as evidenced by their agitated behaviour. Once a sensitive assay has been developed, large numbers of the insects can be bred or collected to provide a source of pheromones. The whole insect or the glands that secret the pheromones are extracted and the pure pheromone is separated from the hundreds of other compounds in the extract. The structure assignment of the trace amount of purified pheromone is usually based mainly on spectroscopic measurements. As a consequence, the postulated structure must then be confirmed by an unambiguous synthesis . the final objective of the project is to device a synthesis for the preparation of large amounts of the pheromones to use for the insect control.

This description is an oversimplification that assumes pheromone to be a single compound. However the sex pheromone of the boll weevil, for example is a mixture of four compounds. No attractive power is observed if one of the components is missing. Occasionally , masking agents are present that inhibit the effectiveness of the pheromones. A major problem is that the insect produces other compounds that are structurally similar and difficult to separate from to biologically active compounds. Sometimes only after the completion of the total synthesis of a biologically inactive compound is it discovered that pheromone was present as a lesser contaminant in the compound whose structure was determined. Pheromones literature is replete with controversy because of these chemical difficulties and in many instances incorrect structures have been assigned to the pheromones.

Examples of pheromones:-

The sex pheromone of the boll weevil has been studied extensively. This insect is important because of the extensive cotton crop lapses that it causes each year. The sex pheromone of the pink billworm moth, another predator of cotton has been identified as a mixture of cis-cis and cir-trans isomers of 7, 11, hexadecadienyl acetate. Cis-7-hexadecyl acetate also attracts the male and was originally believed to be a pheromone, and it is currently being used as an attractant under the commercial name hexalure . Recent attempts to detect hexalure in the extract of 1.2 million pink bollworm moths proved unsuccessful.


Pheromones have been used in three different approaches to insect control:-

to monitor the population of a specific insect the pheromone is placed in traps and the number of insects traps is recorded. The population density of the insect can be monitored in this way to measure the effectiveness of the insecticides being used to control or to monitor in insect migration into new areas;

to trap males a large number of traps containing the pheromones are used to trap all the males in an areas so that they are available for mating

for male confusion large amounts of the pheromone are distributed so the air is permeated with the female sex pheromone. The male is surrounded by attractant and is unable to locate the female.  



Effective use of pheromone-baited traps requires much more than simply placing the traps.

Placement of Pheromone Traps:

Pheromone traps are effective tools for monitoring stored product pests, especially moths, such as Indian meal moths and Mediterranean flour moths. Pheromone traps are often used in food warehouses and food processing facilities.

In such sites, place traps in a grid pattern to pin point the new infestations. If vertical support beams are present, use them to set a grid pattern. Many warehouses have 40-foot by 60-foot bays established by their vertical supports. Some warehouses do not have vertical support beams, and in these cases, the pallet racking or other means can be used to secure a natural grid for a pheromone trapping program. Many warehouses have fire extinguishers set evenly around the warehouse that will offer a site for a trap. The size of the grid will vary with the type of trap and the facility, but as a general rule, intervals of about every 50 feet produce good results. If an area seems to have an infestation, more traps should be placed around that location to help zero-in on the infested goods.

Traps should also be placed near potential insect harborages, such as corners, beams, and entry and exit points (e.g., corridors). As a rule, traps for flying insects should be placed at a height of about 6 feet. Avoid placing traps near exterior doors and windows, as this could lure insects from outdoors.

The use of pheromone traps should not be limited to large food ware-houses and food processing plants. They can be useful as well in smaller facilities such as restaurants, grocery stores, health food stores, pet stores, and even private homes. A few well-placed traps can be an early warning system to detect newly arrived infested goods and prevent wider infestations.

. http://www.insectslimited.com/66%20History%20of%20Pheromones%20Article.htm

Outdoor Trapping with Pheromone Traps:

Like the outdoor rodent control trapping, outdoor pheromone trapping can be very important in a complete pest management program. Insects are naturally present outdoors feeding on grass seed, dead animals, bird nests, pollen, and spilled grain. The purpose of an outdoor trapping program is four fold: (1) to mass trap as many target pests as possible so that they do not enter the building; (2) to intercept the target pest from truck doors and other openings around the building; and (3) to pull insects from in-side the building out into the traps; (4) an awareness tool to show why doors should be closed.

It is useful for the pest management professional to place a pheromone trap inside or outside his home or office. A quick glance into the trap each day will provide a source of valuable information i.e. when the next generation of target pests has emerged in that geographic region.



Determination of the presence, or absence, of potentially harmful pest insects is needed wherever stored commodities are held for extended periods of time. Pheromone traps are excellent tools for this purpose.

All pheromone traps were not created equal. Traps for moths may perform differently than beetle traps. Pest management professionals cannot treat all stored-product pests the same when it comes to recommending an effective trapping program. Long-lived insect adults (e.g., flour beetles) tend to be less attracted to pheromone traps than short-lived insect adults. A flour beetle adult that lives for 12 to 18 months does not react as dramatically to a pheromone lure as an Indian meal moth adult that may only live for one or two weeks.  Beetles tend to use aggregation pheromones where as moths use sex-attractants. The Pantry Patrol corner trap and the new PC Traps are good tools for stored product beetles.


KNOWING THE PEST . Knowing the pest is half the battle in controlling it when establishing and managing a grain, bulk commodity, or bagged product pest management program. This fact holds true when interpreting the results and data from a pheromone monitoring program.

For example: Many adult male beetles emerges from the pupae stage five to seven days before the female. When males are captured in pheromone traps, there will be a five-to seven-day period to find the infestation and implement control measures before the reproductive adult females emerge looking for a mate.


TRAP MAINTENANCE. It is important to change pheromone lures on a periodic basis. The length of time specific lures last can range from 4 weeks to 1 year depending on the manufacturer, the sensitivity of the pheromone, and the type package that the lure is stored in. A good rule of thumb for pheromone lure effectiveness is 8 weeks indoors and 4 weeks outdoors. The ideal lure will release a consistent amount of pheromone during the effective duration giving equal. The date when the trap was placed in service should be noted on the trap it with a "magic marker" type pen (see picture). Other record keeping information should not be written directly on the traps as such a practice will only allow unauthorized individuals access to the results of the trapping program. Trap catch information should be maintained on a trap log or computer software each week.

Many lures normally have some pheromone left in them after eight weeks. The old lure can be left in the trap and a new lure can be placed next to the old lure. Discarded lures should be placed into a sealed plastic bag and discarded in an outdoor trash receptacle. The pheromone trap itself should be discarded when it has captured so many insects that it has lost its ability to hold the target pest. Traps also should be discarded if they begin to have a poor appearance from dirt, scales from moth wings, or from physical damage. Fresh looking traps offer an appearance that a pest management program is well maintained.

Each week, freshly captured insects should be removed from the trap, as this helps in accurately counting newly captured insects the following week. Another reason to remove the insects from the trap each week and replace the traps periodically is that regulatory and quality control inspectors feel more confident about the facility's control program when they see clean traps compared to those filled with insects

TYPES OF TRAPS. It is important to recognize that no one type of trap is best to use in a pest monitoring program in warehouses. It is important to match the specific trap to the particular conditions in each trapping situation. Some examples include: 1) dusty versus non-dusty area; 2) hot versus cold temperatures; and 3) outdoor versus indoor use 4) crawling vs. flying insects 5. sex-attractant vs. aggregation pheromones.

OUTDOOR TRAPS. Trapping for stored-product insects around the outside of a food warehouse can offer several advantages in an overall pest management strategy. The trap selected for outdoor trapping must be able to withstand the weather and should not be prone to becoming saturated with insects quickly.

By placing pheromone traps on the outer perimeter of a storage facility, potentially destructive insects can be intercepted or lured away from stored food and grain. A feral population of many of the most common stored-product insect pests is present outdoors throughout the United States and Canada . Thus, the outdoor  pheromone trapping technique can help the modern pest manager predict the arrival of indoor populations of insects and prevent many from causing an infestation.

TRAP PLACEMENT. No particular number of traps is right for any particular warehouse to detect the presence or absence of pest insects. The number of traps needed changes according to several factors including:      

1) Quality assurance standards by management.

2) Agricultural products versus finished goods.

3) Pharmaceutical versus raw intermediate products.

4) Regulatory pressure


Sex Attractants

Hundreds of pheromones are known with which one of the sex 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:

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 for against a wide variety of the 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.

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

the amount needed

damage to the crop

cost to the grower

possible damage to the environment.

. http://www.insectslimited.com/66%20History%20of%20Pheromones%20Article.htm

These techniques are only effective if there is a low population of the insect to be controlled. The male confusion technique does not work where the insect population is sufficiently large for the male to see the female because it has been shown that males are attracted to any females in sight. The likelihood of spotting a female is obviously higher in a large population density region of a particular insects.

All three approaches are currently being used or tested for the control of the gypsy moth in low infestation areas of moth. The trap contain 20ug of attractant in a control release agent that releases it over one season. The trap also contains a sticky material to hold the moth once it flies into the trap. The male confusion technique has been tested on a small scale with encouraging results. Significantly, fewer females laid fertile eggs in the area where disparlure was sprayed. It should be emphasized that other methods of control will probably be required in areas of heavy infestation.


Pheromones have the advantage of being very specific for one insect and in most cases only very small amount are required. Some scientists have express the opinion that the insects will not develop resistant strain because the pheromone is produced naturally by the insect. However , others note insects have rapidly developed resistance to the synthetic pesticides and see no reason why they should not develop varieties that do not respond to those pheromones. However , even the pessimists agree that it will probably take longer for the insects to develop resistances to pheromones than it took for them to develop resistance to the second generation insecticides.