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.

Sea buckthorn, Hippophae rhamnoides L., has considerable potential for landscape reclamation, food, medicinal, and cosmetics industries. In this study, we analyzed fungal microorganism populations associated with carposphere of sea buckthorn harvested in Lithuania. An amplicon metagenomic approach based on the ITS2 region of fungal rDNA was used to reveal the ripening-affected fungal community alterations on sea buckthorn berries. According to alpha and beta diversity analyses, depending on the ripening stage, sea buckthorn displayed significantly different fungal communities. Unripe berries were shown to be prevalent by Aureobasidium, Taphrina, and Cladosporium, while ripe berries were dominated by Aureobasidium and Metschnikowia. The selected yeast strains from unripe and mature berries were applied for volatile organic compounds identification by gas chromatography and mass spectrometry techniques. It was demonstrated that the patterns of volatiles of four yeast species tested were distinct from each other. The current study for the first time revealed the alterations of fungal microorganism communities colonizing the surface of sea buckthorn berries at different ripening stages. The novel information on specific volatile profiles of cultivable sea buckthorn-associated yeasts with a potential role in biocontrol is important for the development of the strategies for plant cultivation and disease management, as well as for the improvement of the quality and preservation of the postharvest berries. Management of the fungal microorganisms present on the surface of berries might be a powerful instrument for control of phytopathogenic and potentially antagonistic microorganisms affecting development and quality of the berries.

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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.

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Many insects face the challenge to select oviposition sites in heterogeneous environments where biotic and abiotic factors can change over time. One way to deal with this complexity is to use sensory experiences made during developmental stages to locate similar habitats or hosts in which larval development can be maximized. While various studies have investigated oviposition preference and larval performance relationships in insects, they have largely overlooked that sensory experiences made during the larval stage can affect such relationships. We addressed this issue by determining the role of natal experience on oviposition preference and larval performance relationships in a tritrophic system consisting of Galerucella sagittariae, feeding on the two host plants Potentilla palustris and Lysimachia thyrsiflora, and its larval parasitoid Asecodes lucens. We firstly determined whether differences in host‐derived olfactory information could lead to divergent host selection, and secondly, whether host preference could result in higher larval performance based on the natal origin of the insects. Our results showed that the natal origin and the quality of the current host are both important aspects in oviposition preference and larval performance relationships. While we found a positive relationship between preference and performance for natal Lysimachia beetles, natal Potentilla larvae showed no such relationship and developed better on L. thyrsiflora. Additionally, the host selection by the parasitoid was mainly affected by the natal origin, while its performance was higher on Lysimachia larvae. With this study, we showed that the relationship between oviposition preference and larval performance depends on the interplay between the natal origin of the female and the quality of the current host. However, without incorporating the full tritrophic context of these interactions, their implication in insect fitness and potential adaptation cannot be fully understood.

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For a long time the role of volatile cues for the search of host-plants was underestimated in 2 the day-active butterflies compared to the closely related nocturnal moths, but it is now 3 known that olfactory cues play an important role. The simultaneous acquiring of information 4 from several senses during host-plant search, recognition and acceptance for oviposition 5 requires appropriate design of experiments and sample preparation in order to investigate the 6 effect of a selected type of cues while ensuring that the contribution of other sensory 7 modalities will remain uniform. The goal of this study was to investigate the effect of host- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 design of experiments and sample preparation in order to manipulate and investigate the 10 effect of a selected type of cues while ensuring that the contribution of other sensory 11 modalities will remain uniform (Städler, 2002). 12In the day-active butterflies the role of olfactory cues for host search have long been 13 underestimated, in particular in comparison to the their relatives, the nocturnal moths.14 However, it has recently been shown that volatile compounds also play an important role in 15 attracting ovipositing butterfly females (e.g. Ikeura et al. 2010; Schäpers et al. 2015) and 16 moreover that the brains of females seem to be adapted to distinguishing host odours from 17 other odours (Carlsson et al., 2011 corresponding to 500 leaf equivalents was taken and stored at -14 °C. Methanol was removed 10 from the remaining extract and an aliquot of the concentrate, after being dispersed in 150 ml 11 of Millipore purity water, was extracted successively twice with 150 ml of chloroform 12 (99.9% Carlo Erba Reactifs-SDS, France) followed by 150 ml of isobutanol (99+% Alfa Sampling of volatiles 23Two leaf equivalents of extract and 100 ng of pentadecane as internal standard were added on 24 10 cm 2 of filter paper and when methanol was used as a solvent it was allowed to evaporate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 F o r P e e r R e v i e w 7 hexane (1mg/ml) as control stimuli was used to test the sensitiveness of antennae. Three 1 antennae from three females were each used to test the EAG activity of the plant extract. 2The qualitative analyses were performed using a Varian 3400 gas chromatograph coupled 3 with a Finnigan SSQ 7000 mass spectrometer (Termo-Finnigan, San Jose, CA, USA). The 4 GC was equipped with the same type of capillary column and operated under the same 5 condition as described in the EAG experiment except that Helium was used as the carrier gas 6 with an inlet pressure of 70 kPa. Electron ionization mass spectra were dete...