Sex pheromone biosynthesis in the housefly: Evidence for the regulation of the fatty acyl‐CoA desaturation and elongation system by 20‐hydroxyecdysone

The effects of age, sex, and 20‐hydroxyecdysone treatments on fatty acyl‐CoA desaturation and elongation, key reactions in sex pheromone biosynthesis in the housefly,Musca domestica, were investigated. Radio‐HPLC analyses of the elongation products of [1‐14C] 18: 1‐CoA in the presence of malonyl‐CoA and NADPH by microsomes prepared from 0‐, 1‐, 2‐, 3‐, and 4‐day‐old males and 0‐ and 1‐day‐old female houseflies showed that all even‐numbered monounsaturated fatty acids up to 30 carbons were formed. Insects of these ages and sexes produce alkenes of 27 carbons and longer. When microsomes prepared from females 2, 3, and 4 days old (vitellogenic through postvitellogenic) were used, there was no elongation of [1‐14C] 18: 1‐CoA beyond the 24: 1 fatty acyl moiety. Similarly, neither [1‐14C]22: 1‐CoA nor [14, 15‐3H]24: 1‐CoA were efficiently elongated beyond the 24: 1‐acyl moiety in mature females. Females 2–4 days old produce, as their major alkene, the sex pheromone component (Z)‐9‐tricosene (“muscalure,” Z9‐23 Hy), and they use 24: 1‐CoA as the fatty acyl precursor. The initial precursor for the long chain monoenoic fatty acids is oleic acid. Males treated with 20‐hydroxyecdysone and 2–4‐day‐old females desaturated 18: O‐CoA to 18: 1‐CoA with 36–57% less efficiency than control males or previtellogenic females. These data demonstrate that 20‐hydroxyecdysone is involved in the regulation of (Z)‐9‐tricosene production by altering both desaturation and elongation activities.