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.

Milbemectin is composed of 30% milbemycin A3 and 70% milbemycin A4, exhibiting acaricidal and nematocidal properties effective against adult spider mites, their eggs, and C. elegans, with IC50 values of 5.3, 41.1, and 9.5 µg/ml, respectively. It functions as an allosteric agonist of the Drosophila RDL GABA receptor, and demonstrates efficacy against the pinewood nematode, B. xylophilus, with an LC20 of 0.0781 mg/liter.

Milbemycin oxime is a broad spectrum antiparasitic, used as a veterinary drug.