Catalyzes the conversion of methyl farnesoate to juvenile hormone III acid (methyl (2E,6E)-(10R)-10,11-epoxy-3,7,11-trimethyl-2,6-dodecadienoate) in juvenile hormone biosynthesis. methyl (2E,6E)-farnesoate + O2 + reduced [NADPH--hemoprotein reductase] = H(+) + H2O + juvenile hormone III + oxidized [NADPH--hemoprotein reductase] Inhibited by substituted imidazole inhibitors TH27, KK96 and KK71. Specifically expressed in the corpora allata of at the time of maximal juvenile hormone production by the glands. The enzyme is present in all insects, except in lepidoptera (moths and butterflies), and is specific for methyl farnesoate. Lepidoptera contain the farnesoate epoxidase, which is specific for farnesoate. Belongs to the cytochrome P450 family.