AbstractBiosynthesis of the unusual sex pheromone component (Z)‐5‐tetradecenyl acetate (Z5‐14:OAc) was studied in the tortricid moth,Ctenopseustis herana(Felder&Rogenhofer), by fatty acid methyl ester (FAME) analysis of the pheromone gland, and topical application of various deuterium‐labelled acids to the gland. The only unusual unsaturated FAME found in base‐methanolyzed glands of females was the putative precursor of the pheromone, methyl (Z)‐5‐tetra‐decenoate (Z5‐14:Me). When deuterium‐labelled, myristic, palmitic, stearic, lauric, and oleic acids were applied to the gland, label was incorporated into the pheromone component only from the first three acids (i.e., Z5‐14:OAc could not be biosynthesized from lauric or oleic acids). Furthermore, the amount of label incorporated from the first three acids decreased in the order myristic>palmitic>stearic. Application of labelled myristic acid to the gland resulted in incorporation of label into Z5‐14:Me. These data are consistent with the biosynthesis of Z5‐14:OAc inC. heranaresulting from Δ5‐desaturation of myristic acid, a novel biosynthetic route for a moth sex pheromone component. Regulation of pheromone biosynthesis in this species was also investigated. Decapitation of femaleC. heranaresulted in a significant decline in sex pheromone titre. Injection of female head extract or syntheticBombyx moripheromone biosynthesis‐activating neuropeptide (PBAN) into decapitated femaleC. heranagave a significant increase in pheromone titre, suggesting that pheromone biosynthesis in this species is regulated by a PBAN or PBAN‐like s