Spinosad is a naturally-occurring insecticide found in the the soil bacterium S. spinosa. It is a mixture of the macrocyclic lactones spinosyn A and spinosyn D , which act as agonists of insect nicotinic acetylcholinesterase receptors (nAChRs). Oral administration of spinosad induces toxicity in fruit flies including C. capitata, B. curcurbitae, and B. dorsalis (LC50s = 2.8-4.2, 4.3-5.5, and 3.1-3.3 μg/ml, respectively) but has low toxicity in vertebrates. It also inhibits canine P-glycoprotein (P-gp; IC50 = 0.2 μg/ml). Formulations containing spinosad have been used in the agricultural and veterinary control of insects.
