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 Sugiyamaella casensis sp. nov. (Dipodascales).

Ambrosia beetles (Coleoptera, Curculionidae) form obligate nutritional symbioses with ambrosia fungi cultivated within their galleries. Among them, the pinhole borers (Platypodinae) are predominantly tropical, with only two representatives native to Europe. One of them, the rare and understudied Treptoplatypus oxyurus, primarily colonises Abies alba. We investigated its fungal symbionts using a cultivation-dependent approach. We identified three numerically dominant associates in the prothorax containing mycangia: Candida schatavii, Magnusiomyces fungicola, and a novel member of Ophiostomatales. The latter, Wilhelmdebeerea oxyuri gen. et sp. nov., 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: Blastobotrys sasensis sp. nov. and Sugiyamaella casensis sp. nov., both belonging to the family Trichomonascaceae (Dipodascales). 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 T. oxyurus require confirmation through further studies at additional locations. Our findings reveal a previously undocumented fungal diversity tightly linked to a unique pinhole borer, T. oxyurus, thereby enriching our understanding of the fungi associated with conifer-colonising beetles and their ecological and biotechnological importance.