(E)- and (Z)-6-nonen-2-one: Biosynthetic precursors ofEndo- andexo-brevicomin in two bark beetles (Coleoptera: Scolytidae).

The ability of (E)- and (Z)-6-nonen-2-one to serve as precursors of the common scolytid pheromonesEndo- andexo-brevicomin was examined in vivo. When mountain pine beetles (MPB),Dendroctonus ponderosae Hopkins, or western balsam bark beetles (WBBB),Dryocoetes confusus Swaine, were exposed to [6,7-D2](E)-6-nonen-2-one, theEndo-brevicomin produced was enriched with two deuterium atoms per molecule (as determined by GC-MS), indicating that (E)-6-nonen-2-one served as a precursor of this pheromone. Similarly, when the beetles were exposed to [4,4-D2](Z)-6-nonen-2-one, theexo-brevicomin produced was enriched with two deuterium atoms per molecule. Evidence in support of biological relevance of the latter observation include: (1) (Z)-6-nonen-2-one was found in the volatiles of male MPBs and WBBBs, indicating that this is a natural metabolite; (2) theexo-brevicomin produced by MPB was shown to be of natural (+) chirality by complexation chromatography; and (3) female WBBBs and MPBs (which are not known to produceexo-brevicomin) produced significantly lessexo-brevicomin when exposed to the precursor than did the males.