Fungal Pathogens Associated with Tomicus Species in European Forests: Regional Variations and Impacts on Forest Health

<i>Pinus species</i> are extensively abundant in Europe and, as pioneer trees, prominently influence local ecology. However, pine forests in Lithuania, Montenegro, and Ukraine have been significantly damaged by pine bark beetles (<i>Tomicus</i> sp.), which are closely associated with ophiostomatoid and other pathogenic fungi. This study aimed to identify the diversity of ophiostomatoid and other fungi associated with <i>Tomicus</i> sp. in these three countries. Fungi were isolated from beetles and identified. High-throughput sequencing of ITS2 rDNA yielded 285,828 reads, of which 91,141 high-quality reads were retained, representing 561 fungal operational taxonomic units (OTUs). The most important groups of fungi included ophiostomatoids, yeasts, and plant pathogens. While the fungal communities associated with <i>Tomicus</i> spp. were influenced more by environmental factors than by beetle species, the presence of known pathogens such as <i>Ophiostoma</i> spp. indicates that <i>Tomicus</i> spp. could play a significant role in dispersing harmful fungi. Although the virulence of these fungi may vary, their association with potentially pathogenic species suggests that <i>Tomicus</i> spp. may contribute to forest health decline, especially if environmental conditions or host susceptibility change.