<p style="text-align: justify;"><strong>Aim</strong>: Grapevine decline caused by wood fungi seriously threatens viticulture worldwide. In Spain, the polyphagous borer <em>Xylotrechus</em> <em>arvicola</em> (Coleoptera, Cerambycidae) is becoming a serious pest in different Qualified Designation of Origin (DOC) wine regions. The aim of the present work was to identify the fungal species growing in the galleries excavated by <em>X. arvicola</em> larvae inside the vine branches and investigate the possible relationship between wood pathogenic fungi and this borer.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Wood samples from branches of Tempranillo vines and <em>Prunus pisardi</em> trees affected by the borer <em>X. arvicola</em> were collected in La Rioja DOC vineyards (Northern Spain) and analyzed for the presence of fungi using both morphological techniques and genetic tools based on Internal Transcribed Spacer 2 (ITS2) sequence. Among the 20 different fungal species/isolates identified, 7 belonged to fungi associated with grapevine decline (esca, Petri disease, and <em>Eutypa</em> dieback), 6 were plant pathogens, 6 were saprophytic and one was entomopathogenic (<em>Beauveria bassiana</em>).</p><p style="text-align: justify;"><strong>Conclusion</strong>: The fact that 65 % of the fungi detected inside <em>X. arvicola</em> galleries belong to species recognized as plant pathogens suggests that this borer, in addition to causing a progressive decay of the branches, could facilitate the transmission of plant diseases, further threatening the vineyards by spreading grapevine decline pathogens.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: The present work represents a first step in recognizing the association between the fungal pathogens associated with grapevine decline and the borer <em>X. arvicola</em>, suggesting a possible role of this insect as a vector in the transmission of these fungi.</p>