Revision of Quedius sensu stricto (Coleoptera: Staphylinidae)
Authors: Hansen Aslak K. , Brunke Adam , Simonsen Thomas , Solodovnikov Alexey 
Published: November 2022

We here present the first integrative revision of the subgenus Quedius Stephens, 1829 sensu stricto where taxonomic decisions are based on morphology, genomic phylogeny (published elsewhere) and single locus DNA evidence. The subgenus is restricted to the Holarctic region and includes some of the largest, most robust members of the genus Quedius. For species delimitation, a total of 200 COI barcodes covering nearly all species within the subgenus were evaluated through phylogenetic, cluster and network analysis. Taxonomic, distributional and bionomic data, all hitherto published and new are synthesized and an identification key is constructed for all species. All 20 species of Quedius s. str. are divided into five species groups based on genomic phylogeny, morphology, distributional patterns and practical considerations. Overall, there was good congruence among various lines of evidence. As exceptions, high COI barcode variability was found within the wingless and patchily distributed Q. unicolor Kiesenwetter, 1847 and Q. sundukovi Smetana, 2003 (3 and 5 BOLD BINs, respectively) from the Q. molochinus-group without corresponding morphological or geographic patterns. On the contrary, in the Q. pallipes-group very little divergence in the COI barcode was found between clearly morphologically separated species. From the taxonomically challenging Nearctic Quedius molochinoides-group, Quedius altanai Hansen & Brunke sp. nov. is described as new species from the central and southern Rockies, rendering Q. lanei Hatch, 1957 to be restricted to the eastern foothills of the Cascades, Sierra Nevada and Blue Mountains. In the case of Q. subunicolor and Q. altaicus, continuous morphological and COI variation firmly established the earlier suspected synonymy Quedius subunicolor Korge, 1961 = Quedius altaicus Korge, 1962 syn. nov. Other new synonyms established here are: Quedius pallipes Lucas, 1849 = Quedius simplicifrons Fairmaire, 1861 syn. nov. = Quedius levasseuri Coiffait, 1964 syn. nov.; Quedius hispanicus Bernhauer, 1898 stat. reinstituted = Quedius cobosi Coiffait, 1964 syn. nov.; Quedius fuliginosus (Gravenhorst, 1802) = Quedius latus Hochhuth, 1851 syn. nov. = Quedius viduus Sawada, 1965, syn. nov. Quedius gracilis Stephens, 1832 syn. rev. is moved from synonymy with Q. fuliginosus and placed into synonymy with Q. curtipennis Bernhauer, 1908, the younger being the valid name due to prevailing usage in accordance with the ICZN Article 23.9; Quedius hammianus Sharp, 1911 syn. revid., Q. secundus Last, 1952 syn. revid., and Q. rufulus Blümml, 1898 syn. revid., are moved from synonymy with Q. simplicifrons and placed into synonymy with Q. hispanicus Bernhauer, 1898; Quedius sardous Gridelli, 1924 syn. revid., and Q. leonhardi Bernhauer, 1914 syn. revid., are moved from synonymy with Q. molochinus (Gravenhorst, 1806) to synonymy with Q. pallipes. Human mediated dispersals, most likely through the historical transport of ship ballast, are noted as regular phenomenon for some members of the subgenus. Quedius fuliginosus, Q. curtipennis and Q. molochinus, introduced from the Palearctic to the Nearctic, are the most noticeable examples.