Avermectins

Definition

A family of 16-membered macrocyclic lactone compounds produced by fermentation of the soil actinomycete Streptomyces avermitilis, characterized by potent anthelmintic, acaricidal, and insecticidal activity. These natural products occur as homologue pairs (designated a- and b-components) that differ in a single methoxy group at the C5 position; the major commercial derivative, abamectin (avermectin B1), consists predominantly of B1a with lesser B1b. Avermectins act as glutamate-gated chloride channel agonists, causing paralysis and death in nematodes, mites, and insects through hyperpolarization of nerve and muscle cells. Semisynthetic derivatives including ivermectin, doramectin, eprinomectin, and selamectin have been developed for expanded spectrum and improved pharmacokinetic properties in human, veterinary, and agricultural applications.

Etymology

From Streptomyces avermitilis (the producing organism, named for the Japanese 'avermectin' research program) + -in (chemical suffix).

Example

Abamectin, the B1 avermectin mixture, is formulated as an agricultural miticide and insecticide effective against spider mites (Tetranychidae) and leafminers, while ivermectin is widely deployed in mass drug administration programs to control the filarial nematode vectors of onchocerciasis and lymphatic filariasis transmitted by Simulium black flies and Culex mosquitoes.

Related Terms

• macrocyclic lactones
• milbemycins
• spinosyns
• neonicotinoids
• chloride channel agonists
• anthelmintics
• acaricides
• ivermectin
• abamectin
• Streptomyces
• insecticide resistance
• Integrated Pest Management

Usage Notes

Avermectins are distinguished from the chemically related milbemycins by the presence of a disaccharide substituent at C13. In entomological and agricultural contexts, 'avermectin' often refers specifically to abamectin or its emamectin benzoate derivative used against lepidopteran pests. Resistance management is critical: target-site mutations in glutamate-gated chloride channels and enhanced metabolic detoxification have been documented in mites (Tetranychus urticae) and some insect populations. The term is properly plural when referring to the compound family; singular 'avermectin' may denote the structural class or a specific homologue (e.g., avermectin B1a).