Perspectives on the necessity for an integrated management of the two-spotted oak borer, Agrilus biguttatus, and associated research priorities

Forests are affected by novel biotic disturbance agents that require timely evaluation of their relevance and adequate response actions. Oak forests are of particular ecological and economical value and hold great potential for future Central European forests due to their high drought tolerance. Yet, pedunculate and sessile oak ( Quercus robur L.; Q. petraea (Matt.) Liebl.) suffer from recurrent declines. Predisposing, inciting, and contributing factors are manifold. Among the latter, the two-spotted oak borer, Agrilus biguttatus Fabricius, is commonly perceived as a secondary pest. Girdling of the hosts’ vascular tissues by larval feeding might be the proximate cause of death for previously weakened oaks. At high population densities, A. biguttatus might even colonize healthier oaks. Quantitative studies on the causality between A. biguttatus colonization and oak host mortality are still missing and prove challenging to conduct due to A. biguttatus ’ cryptic lifestyle, extended periods of its apparent absence, and its difficult experimental handling. Nonetheless, we perceive an urgent demand for advice from forest practitioners on how to handle A. biguttatus . Reliable early detection methods and action thresholds are deficient, and population control is thus far limited to sanitation felling of unvalidated efficacy. We aim to provide perspectives on the issue by briefly reviewing what is known about the species, evaluating its damage potential, outlining an integrated management, and prioritizing critical research questions. We advocate streamlined research efforts to enhance our understanding and foster progress toward a more sophisticated management. The case of A. biguttatus might ultimately serve as a blueprint for other emerging pests. • Empirical observations indicate A. biguttatus as a mortality agent for weakened oaks, but causality has not yet been proven. • Despite this uncertainty, we examine management options to meet foresters’ demands and prepare for future outbreaks. • We conclude by prioritization of relevant research needs to enhance decision-making and long-term maintenance of oak stands.