Wood-boring insect galleries restructure fungal communities in declining Nothofagus pumilio forests of Patagonia.

Forest decline is often driven by complex interactions among biotic and abiotic factors, including insects and fungi that influence tree health and disease development. In Patagonian forests, decline of Nothofagus pumilio has been associated with wood-boring insects and wood-inhabiting fungi. However, the role of insect galleries in shaping fungal communities within living trees remains poorly understood. Here we characterized fungal communities associated with galleries produced by two wood-boring insects colonizing different woody tissues of living N. pumilio: ambrosia beetles Gnathotrupes spp., which excavate galleries in the sapwood, and the carpenter moth Chilecomadia valdiviana, which develops within the heartwood. Using long-read metabarcoding (ITS and LSU, Oxford Nanopore), we compared fungal assemblages in insect galleries and wood from non-infested trees. Distinct fungal community patterns were associated with each insect species, suggesting that differences in feeding behavior and the woody tissues colonized may influence local fungal community assembly. Galleries of Gnathotrupes were dominated by ambrosia-associated fungi, particularly Raffaelea, along with ophiostomatoid taxa such as Huntiella. In contrast, galleries of C. valdiviana contained a broader assemblage of saprotrophic fungi and yeasts commonly associated with wood decay. These results indicate that different insect feeding guilds shape fungal communities associated with N. pumilio wood and may contribute to the proliferation of opportunistic and potentially pathogenic fungi. This restructuring of fungal assemblages highlights a potential role of insect activity in processes linked to tree decline and disease development in Patagonian forests.