semiochemicals pheromones
TRANSCRIPT
SEMIOCHEMICALS
• Chemicals that modify behavior in any way arereferred to as semiochemicals. Not only chemicalsstimulate but they might also inhibit certainbehaviors.
• Semiochemicals can be divided in two main classes:
• Pheromones: Chemicals that operate intra-specifically. That is, among members of the samespecies.
• Allelochemicals: Chemicals that operate inter-specifically. That is among members from differentspecies.
Introduction
Semiochemicals
Pheromones Allelochemicals
Semiochemicals
• Pheromones
• Allelochemicals
What is a Pheromone?
Defined chemical signal between members of the same species, eliciting a particular behavior or physiological change...”
Pheromone
• A pheromone is a secreted or excreted chemicalfactor that triggers a social response in membersof the same species.
• Pheromones are chemicals capable of actingoutside the body of the secreting individual toimpact the behavior of the receiving individual.
• Their use among insects has been particularly welldocumented. In addition, some vertebrates andplants communicate by using pheromones.
Background
• The term "pheromone" was introduced by PeterKarlson and Martin Lüscher in 1959.
• Pheromone is the Greek word pherein (totransport) and hormone (to stimulate).
• It is also called as ecto-hormones.
• German biochemist Adolf Butenandt hadcharacterized the first such chemical, bombykol, achemically well-characterized pheromone releasedby the female silkworm to attract mates
Classification of Pheromones
• Pheromones are classified based on their function-1) Aggregation pheromone
2) Alarm pheromone3) Epideictic pheromone
4) Releaser pheromone5) Signal pheromone
6) Primer pheromone7) Territorial pheromone
8) Trail pheromone9) Sex pheromone
10) Others pheromone
Sex pheromone
• Sex pheromones are involved in reproduction by attracting the opposite sex.
• In some species female pheromones are used to attract the male.
• In other species male pheromones are used to attract the female.
Pheromones
• Sex pheromone
Alarm pheromone
• Alarm pheromones are used to warn members
of the same species about imminent danger.
• For example the aphids were using an alarm
pheromone to inform other members of their
species that they were attacked by a lady bug!
• As soon as aphids smell this alarm pheromone
they drop from the plant. In this way, even
aphids that are not being attacked by the lady
beetle fall to the ground.
Pheromones
• Alarm pheromone
Aggregation pheromone
• Aggregation pheromones are use to congregate
members of the same species in relatively big
numbers.
• They are used by organisms that need help to
invade a new area or habitat or plant.
• These conifer beetles for example do a better
job, or have a higher fitness when feeding in
group than when feeding individually.
Pheromones
• Aggregation pheromone
Trail pheromone
• Trail pheromones are used by ants to mark
their trails so they can follow each other.
• Have you ever scratch the soil under an ant
trail? Do it and you will see how the ants get
confuse and lost for a while.
Pheromones
• Trail pheromone
Host-marking pheromone
• Host marking pheromones are used by
parasitoids to avoid ovipositing on hosts
they or somebody else have oviposit
already.
• Hyper parasitoids may use these marking
pheromones to find their hosts.
Pheromones
• Host-marking pheromone
1) Aggregation
• Aggregation pheromonesfunction in mate selection,overcoming host resistance bymass attack, and defenseagainst predators.
• A group of individuals at onelocation is referred to as anaggregation, whetherconsisting of one sex or bothsexes.
• Aggregation pheromones havebeen found in members of theArthropods.
Aggregation of bug nymphs
1) Aggregation
• Aggregation pheromones are among the most ecologically selective pest suppression methods.
• They are nontoxic and effective at very low concentrations
Aggregation of bug nymphs
2) Alarm• Some species release a volatile
substance when attacked by apredator that can trigger flightor aggression in members ofthe same species.
• Pheromones also exist inplants: Certain plants emitalarm pheromones whengrazed upon, resulting intannin production inneighboring plants.
• These tannins make the plantsless appetizing for theherbivore.
• Exm. : ants, bees, termites.
4) Releaser
• Releaser pheromones are pheromones that cause analteration in the behavior of the recipient.
• In general, this type of pheromone elicits a rapidresponse, but is quickly degraded.
• For example, some organisms use powerful attractantmolecules to attract mates from a distance of twomiles or more.
5) Signal
• Signal pheromones cause short-term changes,such as the neurotransmitter release thatactivates a response.
• For instance, GnRH molecule functions as aneurotransmitter in rats to elicit lordosisbehavior.
6) Primer
• Primer pheromones trigger a change ofdevelopmental events (in which they differ fromall the other pheromones, which trigger a changein behavior).
7) Territorial
• Pheromones mark the boundaries and identity ofan organism's territory.
• In cats and dogs, these hormones are present inthe urine, which they deposit on landmarksserving to mark the perimeter of the claimedterritory.
8) Trail
• Trail pheromones are common in social insects.• As long as the food source remains, the
pheromone trail will be continuously renewed.• The pheromone must be continuously renewed
because it evaporates quickly.• For example, ants mark their paths with these
pheromones, which are volatile hydrocarbons.Certain ants lay down an initial trail ofpheromones as they return to the nest withfood.
• This trail attracts other ants and serves as aguide.
9) Sex
• In animals, sex pheromones indicate the availabilityof the female for breeding.
• Male animals may also emit pheromones thatconvey information about their species andgenotype.
Allelochemicals
• Alomones-benefit sender
• Kairomones-benefit the receiver
• Synomones-benefit both
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