Beyond <i>Agrilus</i> : exploring the potential role of other oak-associated beetles in the dissemination of Acute Oak Decline-related bacteria

Abstract Acute Oak Decline (AOD) is a complex disease affecting oak trees across Europe, involving a consortium of bacterial species and interactions with wood-boring insects. While Agrilus biguttatus has been widely associated with AOD, the potential involvement of other beetles remains poorly understood. This study investigated the presence of four AOD-related bacteria—Brenneria goodwinii, Gibbsiella quercinecans, Rahnella victoriana, and Lonsdalea quercina—in five oak-associated beetle species (Agrilus biguttatus, A. sulcicollis, Xyleborus monographus, Platypus cylindrus, and Gasterocercus depressirostris) using qPCR detection and multivariate analyses. The results revealed significant differences in bacterial composition among beetle species (PERMANOVA, P = .013). The ambrosia beetles X. monographus and P. cylindrus exhibited the highest diversity and frequency of AOD-related bacteria, suggesting their potential as passive vectors, whereas Agrilus species showed limited bacterial associations. No AOD-related bacteria were detected in G. depressirostris. These findings indicate that the dissemination of AOD-associated bacteria is likely a multifactorial process involving diverse insect–microbe–host interactions rather than a single vector species. Understanding these ecological relationships can improve early detection, risk assessment, and management strategies for oak decline in European forests.