An unusual mechanism for hydrocarbon biosynthesis is proposed from work examining the formation of (Z)-9-tricosene (Z9-23:Hy), the major sex pheromone component of the female housefly, Musca domestica. Incubation of (Z)-15-[1-'4C1-and (Z)-15- [15,16-3H2jtetracosenoic These data demonstrate an unusual mechanism for hydrocarbon formation in insects in which the acyl-CoA is reduced to the corresponding aldehyde and then carbon-1 is removed as CO2. The requirement for NADPH and 02 and the inhibition by CO and the antibody to cytochrome P450 reductase strongly implicate the participation of a cytochrome P450 in this reaction.Long-chain hydrocarbons are abundant components in the cuticular lipids of plants and insects (1, 2), where they function to prevent water loss from the surface of the organism. In some insect species, including the housefly, Musca domestica, hydrocarbon components function as sex pheromones. The main component of the sex pheromone produced by the female housefly is (Z)-9-tricosene (Z9-23:Hy) (3), which functions as a short-range attractant and stimulant (4). In vertebrates, hydrocarbons function in the myelin sheath of peripheral nerves (5) and as components of uropygial gland secretions (6).The mechanism for hydrocarbon biosynthesis has proven to be elusive. Studies in the 1920s (7) suggested that two fatty acids condense head-to-head to form a ketone that is then reduced to the alkane. In an elegant series of experiments in the 1960s (reviewed in ref. -8), Kolattukudy and coworkers demonstrated that hydrocarbons are formed by the elongation of fatty acids, which are then converted to hydrocarbon by the loss of the carboxyl group, which was presumed to be a decarboxylation reaction (9,10). More recently, Kolattukudy and coworkers have obtained evidence from studies in a microorganism (11,12), a plant (13), a vertebrate (6), and an insect (14) that long-chain fatty acyl groups are reduced to aldehydes and then converted to hydrocarbons by a reductive decarbonylation mechanism. This mechanism does not require reduced pyridine nucleotides, and the carbonyl carbon is released as CO. In contrast, Gorgen and coworkers (15,16) presented evidence that 1-alkenes are formed by a decarboxylation mechanism in both plants and insects. We present evidence in this paper that hydrocarbon formation in the housefly occurs by the reduction of a long-chain acyl-CoA to an aldehyde that is then converted to the hydrocarbon and CO2 by a reaction that requires NADPH and 02 and involves cytochrome P450.

The California five-spined ips, Ips paraconfusus Lanier, produces the myrcene-derived acyclic monoterpene alcohols ipsenol (2-methyl-6-methylene-7-octen-4-ol) and ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol) as components of its aggregation pheromone. The pine engraver beetle, Ipspini (Say), produces only ipsdienol. Previous studies have shown that myrcene, a monoterpene in the pines colonized by these beetles, is a direct precursor to these pheromone components. In vivo radiolabeling studies reported hereshowed that male I. paraconjifsus incorporated [1_14C]acetate into ipsenol, ipsdienol, and amitinol (trans-2-methyl-6-methylene-3,7-octadien-2-ol), while male I. pini incorporated [1-_4C]acetate into ipsdienol and amitinol. Females of these species produced neither labeled nor unlabeled pheromone components. The purified radiolabeled monoterpene alcohols from males were identified by comparison of their HPLC and GC retention times with those of unlabeled standards. HPLCpurified fractions containing the individual radiolabeled components were analyzed by GC-MS and were shown to include only the pure alcohols. To further confirm that ipsdienol and ipsenol were radiolabeled, diastereomeric ester derivatives of the isolated alcohols were synthesized and analyzed by HPLC and GC-MS. After derivatization of the radiolabeled alcohols, the HPLC analysis demonstrated expected shifts in retention times with conservation of naturally occurring stereochemistry. The results provide direct evidence for de novo biosynthesis of ipsenol, ipsdienol, and amitinol by bark beetles. The aggregation pheromone components (4S)-(-)-ipsenol(2-methyl-6-methylene-7-octen-4-ol) (1) and (4S)-( + )-ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol) (2) were isolated and identified from males of the California five-spined ips, Ips paraconfusus Lanier. These components, together with (1S,2S)-(+)-cis-verbenol (cis-4,6,6-trimethyl bicyclo[3.1.1]-hept-3-en-2-ol), were identified as the first coleopteran pheromone (1). The structural similarity of the acyclic monoterpene alcohols ipsenol and ipsdienol to myrcene (2, 3), a monoterpene present in the oleoresin of the principal host, ponderosa pine, Pinus ponderosa Laws., led to a deuterium labeling study with I. paraconfusus that unequivocally showed the in vivo transformation of myrcene to ipsenol and ipsdienol (4). A more recent labeling study demonstrated the conversion of myrcene to ipsdienol in the male pine engraver beetle, Ips pini (Say) (5). Recent reviews (6-9) emphasize the central role of plant-derived myrcene in the production of ipsenol and ipsdienol, including the hypothesis that myrcene from the host may be sequestered and bioaccumulated by males during early developmental stages for later use as adults (9 consistent with the general concept that monoterpenes sensu stricto are plant products (7,10,11).However, it has been recognized that alternative routes for Ips spp. pheromone biosynthesis may exist, such as de novo biosynthesis or utilization of other terpene hydrocarbo...

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Pheromone production and/or release by beetles is coordinated with a variety of behavioral, physiological, and environmental factors. To data, two basic mechanisms for the regulation of pheromone biosynthesis in beetles have been proposed. Pheromone biosynthesis may simply be dependent on the availability of biosynthetic precursors. Alternatively, certain stimuli or events may trigger pheromone biosynthesis via juvenile hormone (JH) action. JH may either act directly at the site of pheromone biosynthesis to enhance pheromone production or may act indirectly, through a brain hormone (which might be related to the pheromone biosynthesis activating neuropeptide) or through effects on antennal sensory response. Knowledge of the regulation of the initiation and termination of pheromone biosynthesis is reviewed. Mechanisms by which pheromone stereochemistry is controlled are also discussed. This is an important aspect of pheromone production in Coleoptera, since slight changes in the stereochemistry can completely alter the activity of the molecule. © 1994 Wiley‐Liss, Inc.

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