An allomone is any chemical produced and released by an individual of one species that affects the behaviour of a member of another species to the benefit of the originator. Production of allomones is a common form of defence, particularly by plant species against insect herbivores.

Many insects have developed ways to defend against these plant defenses (in an evolutionary arms race). One method of adapting to allomones is to develop a positive reaction to them; the allomone becomes a kairomone. Others alter the allomones to form pheromones or other hormones, and yet others adopt them into their own defensive strategies, for example by regurgitating them when attacked by an insectivorous insect.

Examples

• Antibiotics

Disrupt growth and development and reduce longevity of adults eg. toxins or digestibility reducing factors.

• Antixenotics

Disrupt normal host selection behaviour eg. Repellents, suppressants, locomotory excitants.

Plants producing allomones

• Desmodium (tick-trefoils)

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