Insect Pheromone
Insect Pheromone
A pheromone (from Greek φέρω phero "to bear" + hormone from Greek ὁρμή - "impetus") is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are hormones capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual. 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. In addition, some vertebrates and plants communicate by using pheromones.
Background
The term "pheromone" was introduced by Peter Karlson and Martin Lüscher in 1959, based on the Greek word pherein (to transport) and hormone (to stimulate). They are also classified as ecto-hormones. These chemical messengers are transported outside of the body and result in a direct developmental effect on hormone levels or behavioral change. They proposed the term to describe chemical signals from conspecifics which elicit innate behaviours soon after the German Biochemist Adolf Butenandt characterized the first such chemical, Bombykol (a chemically well-characterized pheromone released by the female silkworm to attract mates).
Limits
There are physical limits on the practical size of organisms employing pheromones, because at small sizes pheromone diffuses away from the source organism faster than it can be produced, and a sensible concentration accumulates too slowly to be useful. So, bacteria are too small to use pheromones as sex attractants but do use them to determine the local population density of similar organisms and control behaviors that take more time to execute (quorum sensing). Similarly, the simple animals rotifers are apparently also too small for females to lay down a useful trail, but in the slightly-larger copepods the female leaves a trail that the male can follow.
Types
Aggregation pheromones
Aggregation pheromones function in 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. Most sex pheromones are produced by the females and small percentage of sex attractants are produced by males. Aggregation pheromones have been found in members of the Coleoptera, Hemiptera, Dictyoptera and Orthoptera. In recent decades, the importance of applying aggregation pheromones in the management of the boll weevil (Anthonomus grandis), stored product weevils (Sitophilus zeamais ), Sitophilus granarius, Sitophilus oryzae and pea and bean weevil (Sitona lineatus) has been demonstrated. Aggregation pheromones are among the most ecologically selective pest suppression methods. They are not toxic and they are effective at very low concentrations.
Alarm pheromones
Some species release a volatile substance when attacked by a predator that can trigger flight (in aphids) or aggression (in ants, bees, termites) in members of the same species. 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.
Epideictic pheromones
Epideictic pheromones are 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."
Releaser pheromones
Releaser pheromones are pheromones that cause an alteration in the behavior of the recipient. For example, some organisms use powerful attractant molecules to attract mates from a distance of two miles or more. This type of pheromone generally elicits a rapid response but is quickly degraded. In contrast, a primer pheromone has a slower onset and a longer duration. Ex. Rabbit (mothers) release mammary pheromones that trigger immediate nursing behavior by their babies.
Signal pheromones
Signal pheromones 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.
Primer pheromones
Primer pheromones trigger a change of developmental events (in which they differ from all the other pheromones, which trigger a change in behavior).
Territorial pheromones
Laid down in the environment, territorial pheromones 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. In social seabirds, the preen gland is used to mark nests, nuptial gifts, and territory boundaries with behavior formerly described as 'displacement activity'.
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.
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.So that the species will know of who owns that area or who that territory is being occupied by.
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.
At the microscopic level, male copepods can follow a three-dimensional pheromone trail left by a swimming female, and male gametes of many animals use a pheromone to help find a female gamete, for fertilization.
Many insect species release sex pheromones to attract a mate, and many lepidopterans (moths and butterflies) can detect a potential mate from as far away as 10 kilometers (6.25 mi). Traps containing pheromones are used by farmers to detect and monitor insect populations in orchards.
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. Sea urchins release pheromones into the surrounding water, sending a chemical message that triggers other urchins in the colony to eject their sex cells simultaneously.
Other pheromones
This classification, based on the effects on behavior, remains artificial. Pheromones fill many additional functions.
- Nasonov pheromones (worker bees)
- Royal pheromones (bees)
- Calming (appeasement) pheromones (mammals)
- Necromones consisting of Oleic and Linoleic Acids helping animals identify the presence of a dead conspecifics. (Crustaceans and Hexapods)
Uses
Non-human animals
Pheromones of pest insect species, such as the Japanese beetle and the gypsy moth, can be used to induce many behaviors. As a result, a pheromone trap can be used to trap pests for monitoring purposes, to control the population by creating confusion, to disrupt mating, as well as to prevent further egg laying.
In mammals and reptiles, pheromones may be detected by the vomeronasal organ (VNO), or Jacobson's organ, which lies between the nose and mouth and is the first stage of the accessory olfactory system. Some pheromones in these animals are detected by regular olfactory membranes.
Humans
Few well-controlled scientific studies have ever been published suggesting the possibility of pheromones in humans.
The best known case involves the synchronization of menstrual cycles among women based on unconscious odor cues (the McClintock effect , named after the primary investigator, Martha McClintock, of the University of Chicago). This study exposed a group of women to a whiff of perspiration from other women. It was found that it caused their menstrual cycles to speed up or slow down depending on the time in the month the sweat was collected; before, during, or after ovulation. Therefore, this study proposed that there are two types of pheromone invol
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