Methyl farnesoate (MF) is an unepoxidated form of juvenile hormone III, which controls reproduction in insects and appears to serve the same function in Crustacea. MF is synthesized by the mandibular organs (MOs) and has been found in the hemolymph of both females and males in more than 25 species of crustaceans. MF is most actively synthesized by females during vitellogenesis. MF appears to be an active gonadotropin since implants of MOs into non-reproductives will increase gonad indices. In males, high titers of MF are associated with large reproductive systems and aggressive mating behavior.