Spinosyn A is a naturally-occurring macrocyclic lactone that is a potent insecticide. It acts as an agonist of insect nicotinic acetylcholinesterase receptors (nAChRs), which differ both structurally and functionally from nAChRs in vertebrates. As a result, it has low affinity for vertebrate nAChRs and has limited adverse effects in those animals. Spinosyn A is produced naturally by the fermentation of the bacterium S. spinosa and its chemical synthesis has been described.