Lecture 21: PHEROMONES
Semiochemicals are chemical substances that mediate communication
between organisms. Semiochemicals maybe classified into Pheromones (intraspecific
semiochemicals) and Allelochemics (interspecific semiochemicals).
Pheromones are chemicals secreted into the external environment by an
animal which elicit a specific reaction in a receiving individual of the same species.
Pheromones are volatile in nature and they aid in communication among insects.
Pheromones are exocrine in origin (i.e. secreted outside the body). Hence they
were earlier called as ectohormones. In 1959, German chemists Karlson and
Butenandt isolated and identified the first pheromone, a sex attractant from silkworm
moths. They coined the term pheromone. Since this first report, hundreds of
pheromones have been identified in many organisms. The advancement made in
analytical chemistry aided pheromone research.
Based on the responses elicited pheromones can be classified into 2 groups
a) Primer pheromones: They trigger off a chain of physiological changes in
the recipient without any immediate change in the behaviour. They act through
gustatory (taste) sensilla. (eg.) Caste determination and reproduction in social insects
like ants, bees, wasps, and termites are mediated by primer pheromones. These
pheromones are not of much practical value in IPM.
b) Releaser pheromones: These pheromones produce an immediate change in
the behaviour of the recipient. Releaser pheromones may be further subdivided based
on their biological activity into
Sex pheromones
Aggregation pheromones
Alarm pheromones
Trail pheromones
Releaser pheromones act through olfactory (smell) sensilla and directly act on
the central nervous system of the recipient and modify their behaviour. They can be
successfully used in pest management programmes.
1) Sex pheromones are released by one sex only and trigger behaviour
patterns in the other sex that facilitate in mating. They are most commonly released
by females but may be released by males also. In over 150 species of insects, females
have been found to release sex pheromones and about 50 species males produce.
Semiochemicals are chemical substances that mediate communication
between organisms. Semiochemicals maybe classified into Pheromones (intraspecific
semiochemicals) and Allelochemics (interspecific semiochemicals).
Pheromones are chemicals secreted into the external environment by an
animal which elicit a specific reaction in a receiving individual of the same species.
Pheromones are volatile in nature and they aid in communication among insects.
Pheromones are exocrine in origin (i.e. secreted outside the body). Hence they
were earlier called as ectohormones. In 1959, German chemists Karlson and
Butenandt isolated and identified the first pheromone, a sex attractant from silkworm
moths. They coined the term pheromone. Since this first report, hundreds of
pheromones have been identified in many organisms. The advancement made in
analytical chemistry aided pheromone research.
Based on the responses elicited pheromones can be classified into 2 groups
a) Primer pheromones: They trigger off a chain of physiological changes in
the recipient without any immediate change in the behaviour. They act through
gustatory (taste) sensilla. (eg.) Caste determination and reproduction in social insects
like ants, bees, wasps, and termites are mediated by primer pheromones. These
pheromones are not of much practical value in IPM.
b) Releaser pheromones: These pheromones produce an immediate change in
the behaviour of the recipient. Releaser pheromones may be further subdivided based
on their biological activity into
Sex pheromones
Aggregation pheromones
Alarm pheromones
Trail pheromones
Releaser pheromones act through olfactory (smell) sensilla and directly act on
the central nervous system of the recipient and modify their behaviour. They can be
successfully used in pest management programmes.
1) Sex pheromones are released by one sex only and trigger behaviour
patterns in the other sex that facilitate in mating. They are most commonly released
by females but may be released by males also. In over 150 species of insects, females
have been found to release sex pheromones and about 50 species males produce.
