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 chromatography-electroantennography, 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 oak wood 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.
Highlights
Longhorn beetles (Cerambycidae) constitute important components of forest ecosystems worldwide, where they contribute to the decomposition of dead wood, create microhabitats for other organisms, and are important components of forest food webs (Buse et al 2008; Hogstad and Stenberg 1997)
2,3-hexanedione was consistently present in the headspace collections from male P. sanguineum at a mean ratio of 6:100 to (R)-3-hydroxy-2-hexanone
Our study demonstrates that the male-produced aggregationsex pheromone blends of the longhorn beetles P. sanguineum and P. alni consist of (R)-3-hydroxy-2-hexanone and (R)-2methyl-1-butanol
Summary
Longhorn beetles (Cerambycidae) constitute important components of forest ecosystems worldwide, where they contribute to the decomposition of dead wood, create microhabitats for other organisms, and are important components of forest food webs (Buse et al 2008; Hogstad and Stenberg 1997). Longhorn beetles typically breed in dying or recently. Some longhorn beetles are economically important pests in forestry or agriculture, with high potential to become invasive pest species (Haack 2017). As with many other insect taxa, the potential of some species to become pests has provided the primary motivation to identify pheromones for both endemic and invasive longhorn beetles (Allison et al 2004; Hanks and Millar 2016)
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