Fungi, mostly wood-rotting polypores (bracket fungi); the vast majority of species have a limited, well-defined host range, but a few breed on a wide assortment of fungal spp.(2); see(7) on host relationships
In some species males have horns or other armature on pronota and/or heads and use these to fight in their galleries inside the host fungus(2)
Disclaimer: Dedicated naturalists volunteer their time and resources here to provide this service. We strive to provide accurate information, but we are mostly just amateurs attempting to make sense of a diverse natural world. If you need expert professional advice, contact your local extension office.