Avermectin B1 (Abamectin) is a widely used insecticide and anthelmintic. Avermectin B1 is a mixture of avermectins containing more than 80% avermectin B1a and less than 20% avermectin B1b. These two components, B1a and B1b have very similar biological and toxicological properties. The avermectins are insecticidal and antihelmintic compounds derived from various laboratory broths fermented by the soil bacterium Streptomyces avermitilis. Avermectin B1 is a natural fermentation product of this bacterium.