- Pheromones are chemical messengers secreted or discharged outside the body of the organism that activates a social response in members of the same species.
- The term “Pheromone” (Phero-to carry and hormone-to stimulate) was coined by Peter Karlson and Martin Lüscher in 1959.
- They are ectohormones in nature.
- Both plants and animals can release pheromones
- First sex pheromone was identified in 1959 from silk moth (Bombyx mori) termed as bombykol.
- Plants use pheromones to attract bees and other pollinators to their flowers.
- Some plant pheromones have alike chemistry to animal pheromones.
- Aphrodisiacs are fungi that has an odour nearly alike to androstenol; a sex attractant for pigs and very similar to chemicals that act as sex attractants in humans.
- Both intraspecific and interspecific signals influence many forms of insect behaviour.
- Chemicals engaged in signalling between organisms and affecting behaviour alteration are called semiochemicals.
These are of 2 major types of pheromones:
1)Pheromones – conciliate intraspecific interactions.
2)Allelochemicals – conciliate interspecific interactions.
Evolution of pheromone
- Chemical senses being primitive, are shared by all organisms including bacteria, so animals are pre-adapted to determine chemical signals in the environment.
- Pheromones originate from compounds that originally having other uses or importance.
- Chemical molecules became signal molecules by increasing sensitivity and specificity.
- Signals are acquired from movements, body parts or molecules already in use and are eventually changed in the course of evolution to intensify their signal
function. - Evolution in the senses and response of the receiver which facilitated pheromones to become the mostly acceptable way of communication among animals.
Types of pheromones
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Aggregation pheromones:
- A group of individuals existing at one location is termed as aggregation.
- Released by male and utilized by species with long-lived adults.
- These pheromones function in many ways including mate selection, protection against predators, and conquering host resistance by mass attack.
- Ex: boll weevil (Anthonomus grandis B.) is a oligophagous insect which feeds primarily on cotton, Gossypium hirsutum L. Male boll weevils locate their host plant, feeding ensues and releases aggregation pheromones, grandlure.
- Male or grandlure baited traps have been used for mass trapping the boll weevil for many years. It is the most ecologically selective pest suppression methods as they are nontoxic and effective at very low concentrations.
2) Alarm pheromones:
- Some species are capable of releasing a volatile substance in response to attack of the predator which alerts/triggers other members of same species of the danger.
- Ex: Aphides belonging to Homoptera species secrete (E)- β – farnesene as alarm pheromone. These chemicals are released in air as envoy to help other to escape from danger.
- Certain plants emit alarm pheromones when grazed upon, resulting in tannin production in neighbouring plants. These tannins make the plants less beguiling for the herbivore.
3) Releaser pheromones:
- Releaser pheromone has an immediate impact on the behaviour of the recipient and alters it.
- This type of pheromone shows a swift response, but is degraded in no time.
- Ex: Some organisms use strong attractant molecules to lure mates from a distance of two miles or more.
4) Signal pheromones:
- Signal pheromones results short-term changes, such as the neurotransmitter release that activates a response.
- For example, GnRH molecule act as a neurotransmitters in rats to gain lordosis behaviour (inward curve of the spine).
5) Primer pheromones:
- Triggers a chain of physiological development events that may take days to weeks before an unconcealed response is noticed.
- For example- primer pheromones include stimulation of sperm production in fish, termites cast determination, development rates of locust, menstrual cycles in human and other mammals.
6) Epideictic pheromones (Ovipositor pheromones):
- Also termed as spacing pheromones.
- They are known to repel, rather than attract.
- Capable of regulating population density.
- For examples- in insects, female who lay their eggs in fruits deposit these unknown substance in the territory of the clutch to signal to other females of the same species they should clutch elsewhere.
7) Territorial pheromones:
- These pheromones explains claimed region of specific organism.
- alert other organisms of nearby dominant animals.
- These are helpful to filter other animals, such as an ant from another colony.
- Ex: Dogs deposit territorial pheromones present in their urine on landmarks to mark the boundaries their area.
8) Trail pheromones:
- Recruited by social insects for direction and to employ nest mates to a suitable food source.
- These are mostly vaporous compounds.
- Ex: When species of wasps such as Polybia sericea found new nests, they use pheromones to lead the rest of the colony to the new nesting site.
9) Sex pheromones:
- Particularly related with signalling mating behaviours or dominance.
- These are excreted by an organism to lure an individual of the opposite sex and inspire them to mate with them.
- Generally released by females.
- These are simple and volatile, long chain unsaturated alcohol, acids, benzene derivatives, or bicyclic aliphatic compounds.
- Ex: The female Bombyx mori (silk moth) secretes bombykol, the first sex attractant isolated from natural source. It is released in air to attract the male from distance. The male organ of B.mori is intensely sensitive of bombykol.
Application of Pheromones in Pest management
- Inspecting a population of insects to determine if they are present or absent in an area.
- To detect if enough insects are present to permit a costly treatment.
- To mass trap insects to eliminate large numbers of insects from the feeding and breeding population.
- Example: Relatives of bark beetles called ambrosia beetles have been mass trapped from log sorting and timber processing areas throughout British Columbia. Disruption of mating in populations of insects. Useful in protecting crops and residents. Synthetic pheromone is dispersed into crops and the false odour plumes attract males away from females that are waiting to mate.
- Push-pull, attract and kill are direct plans for pest killing.
- Mating disturbance by creating hindrances can control pests as well.
- The theory of behavioural manipulation can be applicable to lure the natural enemies of pests and increase biological control services in managed agroecosystems.
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