The synonymies of Dolichopus lepidus lepidus Staeger, 1842 — demasculinisations, lectotype designations and a nomen oblitum (Diptera, Dolichopodidae)

Type material of all synonyms of Dolichopus lepidus lepidus Staeger, 1842 was examined, except for D. dissimilipes Zetterstedt, 1843 where no type material was available. Lectotype specimens are designated for D. lapponicus Becker, 1917 and D. uliginosulus Dyte, 1980. The previously proposed, but not directly verified synonymy of D. lapponicus with D. lepidus is here confirmed. Two junior synonyms—D. lapponicus and D. cruralis—were provoked by nematode infections that lead to demasculinisation of the males, which mislead former authors in their descriptions. Demasculinised specimens of the junior synonyms are depicted. To stabilize nomenclature, we propose Dolichopus lepidus as nomen protectum, and the senior synonym but forgotten name D. tibialis Zetterstedt, 1838 as nomen oblitum. We provide insights into the historical background of the Zetterstedt name, based on remarks by Loew on Zetterstedt’s descriptions. Additionally, nematodes were found for the first time in specimens of Dolichopus lepidus lepidus Staeger, 1842 from the Alps, and in specimens of Dolichopus urbanus Meigen, 1824, and D. subpennatus d’Assis Fonseca, 1976 from lowlands (Belgium). Nematode-infected specimens of Dolichopus spp. were previously reported exclusively from Scandinavia, and a boreomontane distribution was then suggested.