The Effect of PBAN on Conversion of Fatty Acyls to Pheromone Aldehydes in Female Manduca sexta

Abstract

The pheromone produced by females of Manduca sexta (L.) (Lepidoptera: Sphingidae) was identified as a blend of the 16-carbon aliphatic aldehydes hexadecanal, (Z)-9-hexadecenal, (Z)-11-hexadecenal, (E)-11-hexadecenal, (E,Z)-10,12-hexadecadienal, (E,E)-10,12-hexadecadienal, (E,E,Z)-10,12,14- hexadecatrienal, and (E,E,E)-10,12-14-hexadecatrienal (Starratt et al. 1979; Christensen et al. 1989a; Tumlinson et al. 1989). Subsequently, we showed that fatty acyl analogs of the pheromone aldehydes are present in the pheromone glands of females from about 3 or 4 days prior to adult eclosion until the adults are 8 days old or until death (Fang et al. 1992). By determining the fate of deuterium-labeled fatty acids applied to the gland, we also found that hexadecanoate is the precursor of the 16-carbon unsaturated pheromone aldehydes and fatty acids produced in the gland. Hexadecanoate is converted to (Z)-11-hexadecenoic acid and (E)-11-hexadecenoic acid by All-desaturases, and (Z)-11-hexadecenoic acid is further desaturated and isomerized to the conjugated diene and triene 16-carbon fatty acids (Fang et al. 1995a). The deuterium labeling studies also showed quite clearly that the fatty acids in the gland were the precursors of the aldehydic pheromones. Normally, the aldehydes are produced and released only during the scotophase when the female is calling. However, injection of pheromone biosynthesis activating neuropeptide (PBAN) at any time of the photoperiod into the abdomens of females of any age resulted in production of the pheromone aldehydes after about an hour (Fang et al. 1992). Our labeling studies indicated, but did not prove, that the role of PBAN in regulating pheromone biosynthesis in this species was to activate the enzymes that convert the fatty acids stored in the gland into the analogous aldehydes.