Host-Specific Fungal Assemblages, Dominated by Ophiostomatoid Taxa, in Scots Pine Bark Beetles from Slovakia Revealed by Metabarcoding

Bark beetles (Coleoptera: Scolytinae) play a dual ecological role in forest ecosystems as disturbance agents and vectors of symbiotic fungi, including blue-stain taxa that affect wood quality and tree health. This study assessed fungal communities specific to four bark beetle species—Ips acuminatus (Gyllenhal, 1827), Ips sexdentatus (Börner, 1776), Ips typographus (Linnaeus, 1758), and Pityogenes chalcographus (Linnaeus, 1761)—colonizing Scots pine (Pinus sylvestris L.) in Slovakia. Fungal DNA was extracted from beetle surfaces and analyzed using ITS2 metabarcoding on the Illumina MiSeq platform to characterize the diversity and structure of associated mycobiota. Alpha- and beta-diversity analyses revealed a taxonomically and functionally rich fungal assemblage dominated by Ascomycota, comprising over one thousand operational taxonomic units. Fungal richness and diversity varied among beetle species: I. typographus and P. chalcographus supported the most diverse communities, I. sexdentatus harbored the least diverse assemblages, and I. acuminatus showed contrasting patterns depending on the index used. Beta-diversity analysis indicated that community composition was primarily structured by beetle species identity, with weaker effects of locality and sampling method. Ophiostomatoid fungi, particularly Geosmithia pallida (G. Sm.) M. Kolařík, Kubátová & Pažoutová, Ophiostoma distortum (R.W. Davidson) de Hoog & R.J. Scheff., and Ophiostoma minus (Hedgc.) Syd. & P. Syd., were consistently prevalent and formed the core mycobiome. Random forest classification and differential abundance analyses confirmed host-specific enrichment of several ophiostomatoid and yeast taxa. Yeasts (e.g., Kuraishia, Candida, Yamadazyma), saprotrophic molds (e.g., Penicillium, Davidiella), and the entomopathogen Beauveria bassiana (Bals.-Criv.) Vuill. also occurred frequently. These findings provide the first DNA-based evidence of host-specific fungal assemblages in Scots pine bark beetles in Slovakia and emphasize their ecological significance for beetle–fungus symbioses and pine forest health.