Allelopathy

Definition

The production and release of biochemicals (allelochemicals) by one organism that influence the germination, growth, survival, or reproduction of other organisms. In the strict sense, the term describes chemically mediated competition, often involving secondary metabolites that are not required for the producer's primary metabolism. In broader usage, it encompasses both inhibitory and stimulatory effects across taxa, including plant-plant, microbe-plant, and animal-animal interactions. In entomological and arachnological contexts, allelopathy frequently operates indirectly: plants deploy allelochemicals against competitors that alter host quality for herbivorous insects, or insects and arachnids sequester or detoxify these compounds for their own defense.

Etymology

From Greek allēl- (of one another, mutual) + -pathy (suffering, feeling); coined by Austrian botanist Hans Molisch in 1937.

Example

Black walnut (Juglans nigra) roots and fallen leaves release juglone, a naphthoquinone allelochemical that suppresses growth of neighboring plants; this chemical alteration of the plant community indirectly affects phytophagous insect assemblages by reducing host plant diversity and altering tissue chemistry available to specialist herbivores.

Synonyms

• chemical interference
• allelochemical interaction

Related Terms

• allelochemical
• secondary metabolite
• Kairomone
• allomone
• synomone
• competition
• plant defense
• Sequestration
• Toxicity

Usage Notes

Specialists often restrict 'allelopathy' to chemically mediated competition (inhibition), distinguishing it from chemically mediated facilitation. In entomology, the term is sometimes avoided in favor of more specific chemical ecology terminology (allomone, kairomone, synomone) when describing insect- or arachnid-produced semiochemicals affecting other species. The broader Molisch definition includes stimulatory effects and cross-kingdom interactions, but narrow usage persists in plant ecology. Distinguish from 'allelochemical,' which denotes the specific compound rather than the phenomenon.