Fig. 1

Relative percentage (%) of trapped A Medetera flies and B Ips typographus beetles in the first subtractive assay. Synthetic compounds emitted by bark beetle-infested Norway spruce (Picea abies) were divided into five different groups (A–E), where group A contained the bark beetle compounds 2-methyl-3-buten-2-ol, (–)-cis-verbenol, ( +)-trans-verbenol, (–)-myrtenol, and ( ±)-ipsdienol; group B the microbial compounds ( ±)-camphor, (–)-terpinen-4-ol, ( +)-terpinen-4-ol, (–)-borneol, and ( +)-borneol; group C the microbial compounds (–)-myrtenal, (–)-verbenone, α-terpineol, geranyl, and acetone; group D the spruce tree compounds ( ±)-α-pinene, (–)-β-pinene, camphene, and terpinolene; and group E the spruce tree compounds α-terpinene, γ-terpinene, (–)-limonene, and ( +)-limonene. A full blend (number 1 in the figure) contained all compounds from the five groups (ABCDE), while blends numbers 2–6 contained only compounds from four of the groups. The X denotes presence of the compounds from a specific group in each blend. The control contained only the solvent heptane. The relative percentage of trapped Medetera and I. typographus, respectively, was calculated for the individual treatments relative to the overall number of trapped specimens at the same test round and site. P-values were calculated by pairwise comparisons between control and synthetic blends using the post-hoc Dunnett’s test following two-way analysis of variance (F = 3.1; P < 0.05)