Notes on distribution and ecology of <em>Phloeotribus caucasicus</em> Reitter, 1891 (Coleoptera, Curculionidae, Scolytinae) in Europe

<em>Phloeotribus caucasicus</em> Reitter, 1891 is a bark beetle (Scolytinae) inhabiting Central, Southern and South−Eastern Europe as well as the Caucasus region and Central Asia. It is trophically associated mainly with trees from the Oleacae family (<em>Fraxinus</em> spp., <em>Olea</em> sp.). It is a locally and rarely observed species, especially in the western part of its range. The paper presents new locations of <em>P. caucasicus</em> in Poland and Georgia, where populations of this species were observed. <em>P. caucasicus</em> has not been recorded in Poland so far, and this site is one of the northernmost in Central Europe. The species was found in the forests of river valleys, where the beetles inhabit the thin branches of the ash <em>Fraxinus excelsior</em>, excavating maternal galleries in the form of a transverse biramous system. The paper includes photographs of beetles and galleries for which size parameters from both locations are given. Information on the ecology of the species was compiled. New locations in Poland were discussed in the context of the widespread phenomenon of ash dieback in Europe, the impact of several years of drought on the condition of tree stands, and climate changes causing the south European species to move northwards. River valleys may play an important role in these phenomena.