The ambrosial mycobiota of Treptoplatypus oxyurus (Coleoptera, Platypodidae): a unique island of fungal diversity revealing Wilhelmdebeerea oxyuri gen. et sp. nov. (Ophiostomatales), and two new yeast species Blastobotrys sasensis sp. nov., and Sugiy

Ambrosia beetles (<i>Coleoptera</i>, <i>Curculionidae</i>) form obligate nutritional symbioses with ambrosia fungi cultivated within their galleries. Among them, the pinhole borers (<i>Platypodinae</i>) are predominantly tropical, with only two representatives native to Europe. One of them, the rare and understudied <i>Treptoplatypus oxyurus</i>, primarily colonises <i>Abies alba</i>. We investigated its fungal symbionts using a cultivation-dependent approach. We identified three numerically dominant associates in the prothorax containing mycangia: <i>Candida schatavii</i>, <i>Magnusiomyces fungicola</i>, and a novel member of <i>Ophiostomatales</i>. The latter, <i>Wilhelmdebeerea oxyuri</i> <b>gen. et sp. nov</b>., was the most abundant and exhibited both leptographium-like and hyalorhinocladiella-like morphs. Additionally, two new yeast species of low abundance and uncertain ecological roles were isolated and described: <i>Blastobotrys sasensis</i> <b>sp. nov</b>. and <i>Sugiyamaella casensis</i> <b>sp. nov</b>., both belonging to the family <i>Trichomonascaceae (Dipodascales)</i>. Multigene and phylogenomics analyses confirmed the distinct taxonomic placement of all three new species. The ecological roles of the identified fungi and the strength of their association with <i>T. oxyurus</i> require confirmation through further studies at additional locations. Our findings reveal a previously undocumented fungal diversity tightly linked to a unique pinhole borer, <i>T. oxyurus</i>, thereby enriching our understanding of the fungi associated with conifer-colonising beetles and their ecological and biotechnological importance.