What is concealed under the name Lochmaea crataegi (Coleoptera: Chrysomelidae)?

Until now, Lochmaea crataegi (Forster, 1771) was considered a transpalaearctic species, while the closely related species L. machulkai Roubal, 1926 was known only from the Caucasus and adjacent regions. The present study establishes that L. crataegi is found exclusively in Western, Central, and Southern Europe, while L. machulkai is distributed in Crimea, the central and southern regions of European Russia, the Caucasus, northern Iran, eastern Turkey, and western Middle Asia. A new species, L. sergeevi sp. nov. , is described from Asian Russia, specifically from the Urals to the Far East. The males of L. sergeevi sp. nov. differ from those of L. crataegi and L. machulkai in the aedeagus, which is much wider than that of L. crataegi , with the maximum width closer located to the apex than in L. machulkai (in dorsal view), and significantly less curved than in both compared species (in lateral view), and in the metatibia which is curved near the mid-length, whereas it is curved closer to the base in both of the compared species. The diagnostic characters of the L. crataegi species–group, as well as those of L. crataegi and L. machulkai , are revised. Color photographs of the diagnostic characters and a distribution map of all species are provided.