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 B_1a, which is the principal constituent of the insecticide abamectin. As used in pesticides, abamectin consists of 80% or more of avermectin B_1a and 20% or less of avermectin B_1b and is called avermectin B₁ (Fisher and Mrozik, 1989). Their structures are shown in Figure 97.2. Chemical modification of avermectin B_1a has yielded a number of semisynthetic materials. Emamectin (4″-epimethylamino-4″-deoxyavermectin B_1a) 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 are given in Table 97.1.

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Figure 97.1. Structure of the natural avermectins.

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Figure 97.2. Structures of ivermectin and abamectin.

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Figure 97.3. Structure of emamectin benzoate.