Abstract:
Longhorn beetles are ecologically important insects in forest ecosystems as decomposers of woody substrates, microhabitat engineers,
and as components of forest food webs. These species can be greatly affected both positively and negatively by modern forestry
management practices, and should be monitored accordingly. Through headspace sampling, coupled gas chromatographyelectroantennography,
gas chromatography-mass spectrometry, and field bioassays, we identified two compounds, 2-methyl-1-
butanol and 3-hydroxy-2-hexanone, that constitute aggregation-sex pheromone attractants of three cerambycid species which breed
primarily in different types of fresh, recently dead oakwood in Northern Europe: Pyrrhidium sanguineum (L.), Phymatodes alni ssp. alni
(L.), and Phymatodes testaceus (L.) (Cerambycinae: Callidiini). Analyses of headspace volatiles collected from live insects indicated that
the male-produced aggregation-sex pheromone of P. sanguineum is a 1–15:100 blend of (R)-2-methyl-1-butanol and (R)-3-hydroxy-2-
hexanone, whereas the corresponding ratios for P. alni were 70–110:100. In field bioassays, adult P. sanguineum and P. alni were
significantly attracted to multiple blends with varying ratios of the two compounds. When tested individually, the compounds were
minimally attractive. In contrast, adult P. testaceus exhibited nonspecific attraction to both of the individual compounds and to different
blends, despite the hydroxyketone not being part of its pheromone, which consists of (R)-2-methyl-1-butanol alone. Overall, our results
suggest that a blend of 50:100 of racemic 2-methyl-1-butanol and 3-hydroxy-2-hexanone is appropriate for parallel, cost-efficient
pheromone-based monitoring of all three species. In particular, these species could serve as useful indicators of how modern forestry
practices affect a whole guild of saproxylic insects that require ephemeral deadwood substrates for successful breeding.
