An allomone is any chemical substance

Chemical substance

In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. They can be solids, liquids or gases.Chemical substances are...

 produced and released by an individual of one species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 that affects the behaviour of a member of another species to the benefit of the originator but not the receiver. 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

Evolutionary arms race

In evolutionary biology, an evolutionary arms race is an evolutionary struggle between competing sets of co-evolving genes that develop adaptations and counter-adaptations against each other, resembling an arms race, which are also examples of positive feedback...

). One method of adapting to allomones is to develop a positive reaction to them; the allomone then becomes a kairomone

Kairomone

A kairomone is a semiochemical, emitted by an organism, which mediates interspecific interactions in a way that benefits an individual of another species which receives it, without benefiting the emitter. This "eavesdropping" is often disadvantageous to the producer...

. Others alter the allomones to form pheromone

Pheromone

A pheromone is a secreted 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...

s or other hormone

Hormone

A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

s, and yet others adopt them into their own defensive strategies, for example by regurgitating them when attacked by an insectivorous insect.

A third class of allelochemical (chemical used in interspecific communication), synomones, benefit both the sender and receiver.

"Allomone was proposed by Brown and Eisner (Brown, 1968) to denote those substances which convey an advantage upon the emitter. Because Brown and Eisner did not specify whether or not the receiver would benefit, the original definition of allomone includes both substances that benefit the receiver and the emitter, and substances that only benefit the emitter. An example of the first relationship would be a mutualistic relationship, and the latter would be a repellent secretion."

Examples

• Antibiotic
  Antibiotic
  An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
  
  s

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.