Description
Abamectin belongs to a general class of closely related macrocyclic lactones either produced directly by the actinomycete Streptomyces avermitilis or generated through semisynthetic modifications (Fisher and Mrozik, 1989). The structure for the natural avermectins is given in Figure 97.1. The basic structural motif of the avermectins is evident in the natural product avermectin B1a, which is the principal constituent of the insecticide abamectin. As used in pesticides, abamectin consists of 80% or more of avermectin B1a and 20% or less of avermectin B1b and is called avermectin B1 (Fisher and Mrozik, 1989). Their structures are shown in Figure 97.2. Chemical modification of avermectin B1a has yielded a number of semisynthetic materials. Emamectin (4?-epimethylamino-4?-deoxyavermectin B1a) benzoate is shown in Figure 97.3. Emamectin and ivermectin differ from avermectin B1 by having only a single bond at the C22C23 position (instead of a double bond). The major manufacturers, trade names, and formulations for abamectin, emamectin benzoate, and ivermectin
