CHANGE IN REDUCTASE-ACTIVITY IS RESPONSIBLE FOR SENESCENT DECLINE IN SEX-PHEROMONE TITER IN THE LIGHTBROWN APPLE MOTH, EPIPHYAS-POSTVITTANA(WALKER)

Sex pheromone titre in the tortricid moth Epiphyas postvittana follows a pattern commonly observed in other species of moths: an increase to a peak some time after eclosion (2-3 days), and then a slow decline a s the female ages. Previous work has shown that this decline is not re gulated by the pheromone biosynthesis activating neuropeptide PBAN. Us ing in vivo and in vitro enzyme assays, and fatty acid methyl ester (F AME) analyses of pheromone precursors in the gland, we have investigat ed this senescent decline in pheromone titre. The enzyme assays have s hown that in older females the fatty acid reductase and fatty acid syn thesis enzyme systems decrease in activity (relative to younger female s), whereas other enzyme systems involved in pheromone biosynthesis, i ncluding limited beta-oxidation (2-carbon chain-shortening), (E)-11-de saturation, and acetylation (by an acetyl transferase) remain unchange d in their activity. Of the two enzymatic processes involved, the more important one contributing to the decline appears to be the fatty aci d reductase. This is consistent with FAME analyses of pheromone glands in old and young females, which show little difference in levels of s aturated FAME, but a significant increase in the level of the putative precursor, (E)-11-tetradecenoate, of the sex pheromone component (E)- 11-tetradecenyl acetate. Thus, this decline in fatty acid reductase ac tivity results in a buildup of the precursor as the female ages. The n ear ubiquity of fatty acid reductases in moth sex pheromone systems su ggests that this may be a common mechanism for the senescent decline o f sex pheromone titre in moths. (C) 1997 Elsevier Science Ltd. All rig hts reserved.