Diochus Erichson 1839

Genus Diochus Erichson, 1839 Diochus Erichson, 1839: 300 (species included: nanus); Casey, 1906: 430 (key to species); Bernhauer and Schubert, 1914: 319 (world catalog; 21 species); Blackwelder, 1943: 455 (type species: nanus); Coiffait, 1972: 368 (type species: nanus; key to species of Western Palaearctic region); Smetana, 1982: 27 (revision species of North America north of Mexico); Downie and Arnett, 1996: 395; Newton et al., 2000: 390 (1 Nearctic species, key); Herman, 2001: 2443 (catalog); Assing, 2003 (revision of the Western Palaearctic species); Smetana, 2004: 624 (Catalogue of Palaearctic Coleoptera); Löbl & Löbl, 2015: 1007 (Palaearctic catalog); Zhou & Zhou, 2016: 3 (key to Chinese species); Irmler, 2017: 4, 57 (key to species groups; key to Neotropical species); Shuai, Nozaki & Tang, 2021 (updated key to Chinese species). Syn.: Rhegmatocerus Motschulsky, 1858: 657 (species included: conicollis, punctipennis, antennatus); Gemminger and Harold, 1868: 608 (synonym of Diochus); Lynch, 1884: 171 (synonym of Diochus); Bernhauer and Schubert, 1914: 319 (synonym of Diochus); Cameron, 1932: 44 (synonym of Diochus); Blackwelder, 1943: 455 (synonym of Diochus; type species fixed as punctipennis Motschulsky, 1858); Coiffait, 1972: 368 (synonym of Diochus); Smetana, 1982: 27 (synonym of Diochus); Smetana, 2004: 624 (synonym of Diochus); Löbl & Löbl, 2015: 1007 (synonym of Diochus). Type species: Rhegmatocerus punctipennis Motschulsky, 1858 fixed by subsequent designation by Blackwelder, 1943: 455. Type species: Diochus nanus Erichson, 1839: 300, fixed by monotypy. Diagnosis. Body slender (Fig 1), narrowed anteriorly and posteriorly, usually small to medium-sized (3−6 mm). Head small, with two paired punctures arranged in a square on the disc, a median elevation between the eyes only present in males, sometimes underdeveloped or absent. Neck cylindrical, thin, about 1/3 width of head, both the dorsal and ventral surface with a ridge or a groove. Pronotum oval shaped, usually with five paired punctures on surface. Elytra not overlapping at suture; each elytron usually with a row of five punctures along suture, a row of five punctures in median. Protarsi moderately dilated. Antesternal plate rudimentaly and weakly sclerotized. Prosternum with distinct intercoxal process and transverse ridge. Mesoventrites with obvious longitudinal ridge, transverse ridge, and oblique furrow. Discrimen of metaventrites distinctly elevated. Aedeagus usually sclerotized, with symmetrical parameres; the structures of aedeagus and the shapes of parameres are usually specific for species. Female spermatheca (Fig 2-2I; Fig 3-2I; Fig 4-2I; Fig 5-2I; Fig 6-2C-D; Fig 9-3I) divided into an outer capsule and a sclerotized tube; the length and the shape of the tube can be different among species. Sternite and tergite VIII broad; posterior margins of male sternite VIII usually specific for species. Tergite IX symmetrical, connected mediobasally, narrowed apically. Sternite IX small, usually asymmetrical in male, but symmetrical in female. Tergite X distinctly broad. Sternite X in female slender and rhomboidal, with numerous setae in lower half, but absent in male. The diagnosis follows Zhou & Zhou (2016).