Pheromone

Pheromone

A pheromone (from

Greek

φ

?

ρ

ω

< br>

phero

hormone

from Greek

?

ρμ

?

-

or

excreted

chemical

factor

that

triggers

a

social

response

in

members

of

the

same

species

.

Pheromones

are

chemicals

capable

of

acting

outside

the

body

of

the

secreting

individual

to

impact

the

behavior of the receiving individual.

[1]

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

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 sometimes 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.

[2]

They

proposed

the

term

to

describe

chemical

signals

from

conspecifics

which elicit innate behaviors 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).

[3]

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.

[4]

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.

[5]

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.

[6]

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

)

[7]

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

.

[8]

Epideictic pheromones

Epideictic

pheromones

are

different

from

territory

pheromones, when it comes to insects.

Fabre

observed

and

noted

how

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.

[9]

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

.

[10]

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

cats

and

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.

[11]

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