Aggregation pheromone of the Oriental spruce engraver Pseudips orientalis

Volatiles from the hindgut extracts of males of the Oriental spruce engraver Pseudips orientalis (Wood & Yin) (Coleoptera: Curculionidae, Scolytinae) of different phases of gallery development were analyzed by gas chromatography-mass spectrometry-flame ionization detection (GC-MS/FID) with both polar and enantioselective columns. GC-MS/FID analyses showed that unmated males or males mated with one female produced approximately 95%-(-)-ipsenol and (-)-cis-verbenol as major components, as well as (-)-trans-verbenol, myrtenol, approximately 70%-(+)-ipsdienol and (-)-verbenone as minor or trace components. The release of these male-produced compounds was confirmed by GC analysis of an aeration sample of a P. orientalis-infested spruce log. Mating reduced production of the male-specific hindgut volatiles. A field-trapping bioassay in Qinghai, China, showed that a ternary blend containing two major components, 97%-(-)-ipsenol (i.e. close to naturally produced enantiomeric ratio) and (-)-cis-verbenol, plus a minor component (-)-trans-verbenol, caught significantly more P. orientalis beetles (male: female = 1: 2.7) compared with the unbaited control. Subtraction of (-)-trans-verbenol from the active ternary blend had no significant effect on trap catches. The addition of (+/-)-ipsdienol (at 0.2 mg/day release) to the active ternary or binary blends significantly interrupted their trap catches. Replacing 97%-(-)-ipsenol with (+/-)-ipsenol in the ternary blend significantly reduced trap catches to a level that was no different from the blank control. Pseudips species were sister to all other Ipini genera in a phylogeny reconstructed with mitochondrial cytochrome oxidase I DNA data for 51 Ipini and outgroup species. The results obtained suggest that the two major components, 95%-(-)-ipsenol and (-)-cis-verbenol (at approximately 4-5 : 1), produced by unmated fed males, are probably the primary aggregation pheromone components for P. orientalis. In light of the phylogeny, the use of terpenoid semiochemicals as pheromones probably occurred early in the evolution of Ipini and these semiochemical blends were subsequently modified in the process of speciation.