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.

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

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The plantation area of sea buckthorn (Hippophae rhamnoides L.) is expanding in many European countries due to increasing demand for berries, thus creating suitable conditions for the rapid expansion of the fruit fly Rhagoletis batava, a pest of economic importance. To decrease insecticide use, effective means for pest population monitoring are required, including the use of pheromones. Male fruit flies emit (-)-δ-heptalactone as revealed by gas chromatography-mass spectrometry analyses of samples obtained using headspace methods. The two enantiomers of δ-heptalactone were synthesized using enantioselective synthesis. A gas chromatography-electroantennographic detection analysis of both stereoisomers revealed that only (-)-δ-heptalactone elicited electrophysiological responses, whereas no signal was registered to (+)-δ-heptalactone in fruit flies of either sex. In the field assay, traps baited with (-)-δ-heptalactone caught significantly more fruit flies compared with the unbaited traps. Our results are the first to demonstrate the efficacy of (-)-δ-heptalactone as a bait for trapping R. batava. As a behaviorally attractive compound to R. batava fruit flies of both sexes, (-)-δ-heptalactone is attributed to aggregation pheromones. This is the first report of an aggregation pheromone within the genus Rhagoletis.