<p>Xylophagous insects, like <i>Monochamus saltuarius</i> significantly affect tree-stem-associated microbial communities and pose major threats to forest ecosystems. As a vector for the pinewood nematode (<i>Bursaphelenchus xylophilus</i>) and a wood-boring pest, <i>M. saltuarius</i> infests various <i>Pinus</i> species. Yet, the interactions between <i>M. saltuarius</i>-associated fungi and the endophytic fungi of its host tree, <i>Pinus koraiensis</i>, remain uncharacterized. In this study, high-throughput sequencing was used to characterize fungal communities within infested and uninfested host trees. Endophytic fungi with lignocellulose-depolymerizing potential were identified, and their enzymatic activity was experimentally assessed. A significant reduction in fungal diversity was detected in infested samples, indicating that <i>M. saltuarius</i> infestation disrupts the native fungal community, favoring plant pathogens and diminishing the abundance of lignocellulosic depolymerizing fungi. To explore ecological shifts and diagnostic taxa, an integrated biomarker discovery framework combining Random Forest and LEfSe analysis was applied. This model revealed fungal biomarkers enriched in uninfested tissues and potentially involved in lignocellulose degradation based on functional annotation and in vitro assays. These taxa may serve as indicators of infestation status and provide insight into host-microbe-insect interactions. These findings contribute to understanding how xylophagous insect infestations restructure fungal communities and offer a model-based approach for detecting ecological signatures of pest impact in forest ecosystems.</p> Graphical Abstract <p></p>