Milbemycin A3 is a member of a complex family of macrocyclic lactones that contain a characteristic spiroketal group produced from the fermentation of soil bacterium S. hygroscopicus subsp. aureolacrimosus. As a compound that potentiates glutamate and GABA-gated chloride-channel opening, milbemycin A3 is used as a nematocide and insecticide. The acaricidal and nematocidal activity of a mixture of milbemycin A3 and milbemycin A4 against adult spider mites, spider mite eggs, and C. elegans are reported at IC50 values of 5.3, 41.1, and 9.5 μg/ml.
