Background:

Avermectins are insecticides and anthelmintics first isolated from broths fermented by S. avermitilis.[1] They potentiate glutamate- and GABA-gated chloride channel opening in nematodes.[2],[3] Avermectin B1b is a minor component of avermectin broth.[2] Avermectins, including avermectin B1b, are used broadly against nematodes, ticks, flies, and ants.[2]

Reference:
[1]. Egerton, J.R., Ostlind, D.A., Blair, L.S., et al. Avermectins, new family of potent anthelmintic agents: Efficacy of the B1a component. Antimicrobial Agents and Chemotherapy 15(3), 372-378 (1979).
[2]. Duke, S.O., Cantrell, C.L., Meepagala, K.M., et al. Natural toxins for use in pest management. Toxins (Basel) 2(8), 1943-1962 (2010).
[3]. Arena, J.P., Liu, K.K., Paress, P.S., et al. The mechanism of action of avermectins in Caenorhabditis elegans: Correlation between activation of glutamate-sensitive chloride current, membrane binding, and biological activity. Journal of Parasitology 81(2), 286-294 (1995).