Is Prey Specificity Constrained by Geography? Semiochemically Mediated Oviposition in Rhizophagus grandis (Coleoptera: Monotomidae) with Its Specific Prey, Dendroctonus micans (Coleoptera: Curculionidae: Scolytinae), and with Exotic Dendroctonus species.

Examples of totally specific predators are rare, and the mechanisms underlying this specificity are often poorly understood. In Eurasia, the Monotomid beetle Rhizophagus grandis is found only in the galleries of its prey, the bark beetle Dendroctonus micans. The specificity of R. grandis relies on kairomones which female predators use to adjust their oviposition to the number of prey larvae available in a gallery. Yet these chemical signals are still largely unknown. The North American D. punctatus and D. valens, which are not sympatric with R. grandis but have a similar ecology as D. micans, could also elicit predator oviposition, which would suggest that specificity in this predator-prey system is constrained by geography. In order to further identify these determinants of specificity, we used artificial oviposition boxes to compare the oviposition level of R. grandis in the presence of larvae of each of the three prey species. We jointly used sequential dynamic headspace extractions and gas chromatography coupled with mass spectrometry to investigate oviposition stimuli associated with each prey species and potential oviposition inhibitors emitted by the predator. We further assessed potential stimuli with the analysis of emissions from D. micans larvae reared alone. Overall, we identified and quantified 67 compounds, mostly terpenes. Several robust candidate stimulants or inhibitors of R. grandis' oviposition were identified. The three prey species elicited similar oviposition levels in R. grandis, which suggests that this predator could form new associations outside of its native range.

Bacterial and fungal symbionts of parasitic Dendroctonus bark beetles.

Bark beetles (Curculionidae: Scolytinae) are one of the most species-rich herbivorous insect groups with many shifts in ecology and host-plant use, which may be mediated by their bacterial and fungal symbionts. While symbionts are well studied in economically important, tree-killing species, little is known about parasitic species whose broods develop in living trees. Here, using culture-dependent and independent methods, we provide a comprehensive overview of the associated bacteria, yeasts and filamentous fungi of the parasitic Dendroctonus micans, D. punctatus and D. valens, and compare them to those of other tree-inhabiting insects. Despite inhabiting different geographical regions and/or host trees, the three species showed similar microbial communities. Enterobacteria were the most prevalent bacteria, in particular Rahnella, Pantoea and Ewingella, in addition to Streptomyces Likewise, the yeasts Candida/Cyberlindnera were the most prominent fungi. All these microorganisms are widespread among tree-inhabiting insects with various ecologies, but their high prevalence overall might indicate a beneficial role such as detoxification of tree defenses, diet supplementation or protection against pathogens. As such, our results enable comparisons of symbiont communities of parasitic bark beetles with those of other beetles, and will contribute to our understanding of how microbial symbioses facilitate dietary shifts in insects.