Revision of the Western Palaearctic species of Orthocentrus Gravenhorst, 1829 (Hymenoptera, Ichneumonidae, Orthocentrinae): species with ivory / yellow marks on the vertex

In the first of a series of papers revising the poorly-studied Darwin wasp genus Orthocentrus Gravenhorst, 1829, in the Western Palaearctic, here we revise species with yellow or ivory marks on the vertex. Several new country records are provided: O. bilineator Aubert, 1959 and O. castellanus Ceballos, 1963 from Italy; O. hirsutor Aubert, 1969 from Italy, Sweden and Ukraine; and O. orbitator Aubert, 1963 from Israel, Italy, Turkey, and Ukraine.

One species, O. mirabilis Varga & Di Giovanni, sp. nov., is described as new from Belgium, Italy, Poland, Sweden, and Ukraine. An identification key, diagnoses and illustrations to all the studied species are provided.