De novo biosynthesis of the aggregation pheromone components ipsenol and ipsdienol by the pine bark beetles Ips paraconfusus Lanier and Ips pini (Say) (Coleoptera: Scolytidae).
Ips paraconfusus 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. Ips pini produces only ipsdienol. Previous studies had shown that myrcene, a monoterpene in the trees (Pinus jeffreyi) colonized by these scolytids, is a direct precursor to these pheromone components. In vivo radiolabelling studies showed that male I. paraconfusus incorporated [1-14C]acetate into ipsenol, ipsdienol and amitinol (trans-2-methyl-6-methylene-3,7-octadien-2-ol), while male I. pini incorporated [1-14C]acetate into ipsdienol and amitinol. Females of these species produced neither labelled nor unlabelled pheromone components. The purified radiolabelled monoterpene alcohols from males were identified by comparison of their HPLC and GC retention times with those of unlabelled standards. HPLC-purified fractions containing the individual radiolabelled components were analyzed by GC-MS and were shown to include only the pure alcohols. To further confirm that ipsdienol and ipsenol were radiolabelled, diastereomeric ester derivatives of the isolated alcohols were synthesized and analyzed by HPLC and GC-MS. After derivatization of the radiolabelled alcohols, the HPLC analysis demonstrated expected shifts in retention times with conservation of naturally occurring stereochemistry.