Aggregation pheromone of the Qinghai spruce bark beetle, Ips nitidus Eggers

Volatiles from hindgut extracts of males of the Qinghai spruce bark beetle, Ips nitidus, from different attack phases (Phase 1: unpaired males and Phases 2-4: males joined with 1-3 females) and hindgut extracts of mated females were analyzed by GC-MS/FID with both polar and enantioselective columns. The GC-MS/FID analyses demonstrated that unpaired males from attack Phase 1 (nuptial chamber constructed) produced 2-methyl-3-buten-2-ol, approx. 74%-(–)-ipsdienol, and (–)-cis-verbenol as major hindgut components, and (–)-trans-verbenol, (–)-ipsenol, (–)-verbenone, myrtenol, and 2-phenylethanol as minor or trace components. The quantities of 2-methyl-3-buten-2-ol and especially ipsdienol decreased after mating during Phases 2-4, whereas the quantities of (–)-cis- and (–)-trans-verbenol did not change. In contrast, the quantity of (–)-ipsenol seemed to increase as mating activity progressed. After mating with three females, only trace to small amounts of male-specific compounds were detected from I. nitidus male hindguts. Chemical analysis of the hindgut extracts of mated females showed no obvious semiochemical production. A field trapping bioassay in Qinghai, China showed that the four-component “full blend” containing the three major components, 2-methyl-3-buten-2-ol, (±)-ipsdienol, and (–)-cis-verbenol, plus a minor component, (–)-trans-verbenol, caught significantly more I. nitidus than did the unbaited control and two binary blends. Replacing (±)-ipsdienol with nearly enantiomerically pure (–)-ipsdienol in the “full blend” significantly reduced trap catches, which suggests that both enantiomers of ipsdienol are needed for attraction. On the other hand, removal of (–)-trans-verbenol from the active “full blend” had no significant effect on trap catches. Our results suggest that the three major components, 2-methyl-3-buten-2-ol, 74%-(–)-ipsdienol, and (–)-cis-verbenol (at 7:2:1) are likely the aggregation pheromone components of I. nitidus.