Abstract& Key message Spruce trees emit significant amounts of trans-4-thujanol, but the amount of this compound in bark decreases with tree age. Trans-4-thujanol acts as an efficient repellent for the bark beetle Ips typographus. & Context The spruce bark beetle, Ips typographus, is an economically significant pest of Norway spruce (Picea abies) that preferentially infests and kills old trees. & Aims We looked for spruce volatiles that were perceivable by I. typographus and that differed as the host tree aged. & Methods Bark beetles were collected in the wild. Bark samples from spruce trees of different age were hydrodistilled. Gas chromatography-electroantennogram detection (GC-EAD) was used to identify which compounds induced beetle olfactory responses. These were identified by gas chromatography-mass spectrometry (GC-MS). Behavioural responses of bark beetles were tested using a Y-tube olfactometer. & Results Several EAD peaks were recorded, of which trans-4-thujanol was consistently active and could be identified chemically unequivocally. The antennae of I. typographus females responded to a lower dosage of the compound than males, but both sexes were repelled by it. The bark of 10-year-old spruce trees contained 3 times more trans-4-thujanol than that of 35-40-year-old trees, 27 times more than that of 70-to 80-year-old trees, and 200 times more than that of 120-year-old trees. & Conclusions Trans-4-thujanol is a bioactive compound in Norway spruce bark that varies in amount with tree age and affects spruce bark beetle behaviour under laboratory conditions. It is suggested that trans-4-thujanol might play a role in both spruce tree defence and tree choice by beetles.

Two components of the female-produced sex pheromone of the hornet moth, Sesia apiformis, were identified as (3Z,13Z)-octadeca-3,13-dien-1-ol (3Z,13Z-18:OH) and (2E,13Z)-octadeca-2,13-dienal (2E,13Z-18:Al), a pheromone structure new in Sesiidae. Pooled gland extracts showed the two major compounds in a proportion of ca. 2:3, while SPME-investigations on single calling females revealed a ratio of ca. 1:7. Although the single compounds were not attractive, a 2:3 mixture proved to be highly active towards males in field tests. Small amounts of (2E,13Z)-octadecadienol (2E,13Z-18:OH) were found in the sex pheromone gland of females, however, the biological significance of the compound remains unclear. Methyl sulfide was found to readily react with 2-alkenals, providing an effective new method for the characterization of this type of compound upon GC/MS. The derivatives, 1,1,3-tris(methylthio)alkanes, are the products of the addition of methyl sulfide to the double bond and the transformation of the carbonyl group into the corresponding bis(methylthio)acetal. The mass spectra of these compounds are characterized by diagnostic signals at m/z 107 and/or m/z 121. These fragments represent the first carbon unit or the first two carbon units of the derivative, respectively. The parent signal in the spectra of thiomethyl derivatives of 2-alkenals showing no other double bonds is represented by m/z M+ - 121, formed upon loss of the first two carbon units. By employing a solution of methyl sulfide in dimethyl sulfide, the double bond positions in 2E,13Z-18:Al could be fully characterized by GC/MS.

Erwinia typographi sp. nov., isolated from bark beetle (Ips typographus) gut

Under an artificial light:dark cycle, females of Lampronia capitella were observed calling, with extended terminal abdominal segments, during the first 2 hr of the photoperiod. Extracts of terminal abdominal segments from females elicited large electroantennographic responses from male antennae. Gas chromatography with electroantennographic detection revealed three active peaks. Based on comparison of retention times and mass spectra of synthetic standards, these compounds were identified as (Z,Z)-9,11-tetradecadienol and the corresponding acetate and aldehyde. The electroantennographic activity of the four geometric isomers of all three compounds was investigated, and the respective (Z,Z)-isomer was found to be the most active in all cases. Aldehydes generally elicited larger antennal responses than alcohols, whereas acetates were the least active compounds. A subtractive trapping assay in the field, based on a 13:26:100 micrograms mixture of (Z,Z)-9,11-tetradecadienal, (Z,Z)-9,11-tetradecadienyl acetate, and (Z,Z)-9,11-tetradecadienol confirmed that all three compounds are pheromone components. Subtraction of (Z,Z)-9,11-tetradecadienol from the blend completely eliminated its attractiveness, whereas the other two-component blends showed reduced activity. This is the first pheromone identification from the monotrysian superfamily Incurvarioidea, confirming that the common pheromones among ditrysian moths (long-chain fatty acid derivatives comprising alcohols, acetates, and aldehydes with one or more double bonds) is not an autapomorphy of Ditrysia, but a synapomorphy of the more advanced heteroneuran lineages.