The Ecology of Beech Bark Beetle Mycobiomes: Similar Fungal Composition Despite Host, Elevation and Site Gradients

Abstract Bark beetles form varying associations with fungi, yet the mycobiomes of many deciduous phloem-feeding species are poorly studied and their ecological significance remains underexplored. Here, we used ITS2 metabarcoding to characterize the fungal communities of the beech bark beetles Ernoporicus fagi and Taphrorychus bicolor collected from 61 forest patches across six regions in Germany. Despite sampling two beetle species across an elevational gradient, experimental forest management treatments, and six regions, beetle species identity, treatment, and elevation explained little variation in beetle mycobiomes, and region showed only a weak effect that disappeared under closer inspection. However, we found mycobiome composition varied more consistently at the finer scale of individual forest sites, and geographic distance between patches had a weak but significant effect, suggesting that the fungal communities these bark beetles carry are shaped by local, patch-level factors rather than broader regional or host-related factors. The mycobiomes of both beetle species were largely similar and dominated by ubiquitous saprotrophs and yeasts.