Allomones

Definition

Semiochemicals produced by one species that alter the behavior or physiology of individuals of a different species, benefiting the emitter but not the receiver. Allomones mediate interspecific interactions where the interests of sender and receiver are opposed, most commonly as defensive compounds that deter predators or herbivores, but also as offensive signals that facilitate prey capture or competitive interference.

Etymology

Greek allos (other, different) + -mone (from pheromone, hormone), coined by Brown, Eisner, and Whittaker (1970) to contrast with pheromones (intraspecific signals).

Example

The bombardier beetle (Brachinus spp.) discharges a hot, noxious spray of benzoquinones from abdominal glands when attacked; these allomones deter ants, spiders, and vertebrate predators without benefit to the aggressor. Plants similarly emit volatile allomones such as green leaf volatiles when damaged by caterpillars, indirectly recruiting parasitoid wasps that attack the herbivore—a tri-trophic allomonal effect.

Related Terms

• kairomones
• synomones
• semiochemicals
• Allelochemicals
• defensive secretions
• aposematism

Usage Notes

The term is defined strictly by fitness outcomes, not chemistry: an identical compound functions as an allomone, kairomone, or synomone depending on which party benefits. Allomones are thus contrasted with kairomones (benefit receiver, not emitter) and synomones (mutual benefit). In entomological literature, 'defensive allomone' is common; 'offensive allomone' for prey attraction is less frequent and sometimes debated. The singular form 'allomone' is standard in chemical ecology, though 'allomones' dominates in ecological and behavioral contexts discussing collective or comparative effects.