Rheocricotopus (s. str.) effusus (Walker, 1856) Chironomus effusus Walker, 1856: 180. Orthocladius (Trichocladius) striatus Malloch, 1915: 517. Cricotopus rivicola Kieffer, 1921: 804. Orthocladius (Dactylocladius) dorieri Goetghebuer in Goetghebuer & Dorier, 1932: 65. Trichocladius holosericeus Goetghebuer in Gouin, 1936: 167. Trichocladius brunensis Goetghebuer, 1937: 275. ? Rheocricotopus himalayenis Chaudhuri & Sinharay, 1983: 398. Syn. nov. Rheocricotopus baishanensis Wang & Zheng, 1991: 102. Syn. nov. Rheocricotopus effusus – Brundin 1956: 118. — Lehmann 1969: 356. — Wang & Zheng 1991: 102. Rheocricotopus (Rheocricotopus) effusus – Saether 1986: 103. — Saether et al. 2000: 161. — Makarchenko & Makarchenko 2005: 129. — Ashe & O’Connor 2012: 569. Type material Holotype of Rheocricotopus baishanensis CHINA – Jilin • ♂; Mt Changbai; 42°0′ N, 128°6′ E; 23 Jun. 1986; NKU. Photographs of the holotype of R. baishanensis provided by X. Lin (SHOU) were examined. Type specimens of Chironomus effusus and R. himalayenis were not examined. Distribution The species is known around the world including Oriental and Palaearctic China, and the Russian Far East. Remarks Makarchenko & Makarchenko (2005: 129) redescribed briefly R. (s. str.) effusus (Walker, 1856) based on adult males from Sakhalin Island in the Russian Far East. Wang & Zheng (1991: 102) also gave a brief redescription of the male based on a specimen from Sichuan Province in Oriental China. The mensural data of the males from both the regions are nearly consistent with those from Europe (Saether 1986: 103; Saether & Schnel 1988: 72, table 1), although the structure of the humeral pit is disregarded in these redescriptions. Wang & Zheng (1991: 102) described R. (s. str.) baishanensis Wang & Zheng, 1991 based on a single male from Jilin Province in Palaearctic China, and wrote: “Allied to R. effusus in AR, LR, but lacking crista dorsalis and the shape of anal superior volsella, caudomesal projection and humeral pit also different.” The photographs of the holotype taken by X. Lin (pers. comm. 2022) show that the hypopygium is mounted somewhat diagonally on the slide. A closer examination of the photographs revealed that the humeral pit is composed of a large and a small hole, and the large hole is elliptical and almost 0.4 × as wide as its length, although wrinkled by the mounting procedure, and that the hypopygium possesses a posteriorly projected, horn-shaped superior volsella on the base of gonocoxite and a low crista dorsalis on the subapex of gonostylus. Rheocricotopus (s. str.) baishanensis is a junior synonym of R. (s. str.) effusus. Further, Liu et al. (2014b: 101) gave a diagnosis and many collection records for the male, not associated with the immature stages, of R. (s. str.) effusus from Palaearctic and Oriental China, but their diagnosis cannot reliably separate the species from R. (s. str.) tamahumeralis Sasa, 1981. There is a possibility that some or all specimens belong to R. (s. str.) tamahumeralis. In both males, the humeral pit consists of a large hole and a small hole. The large hole is elliptical in R. (s. str.) effusus according to Lehmann (1969: 372 fig. 13a), whereas it is triangular or trapezoid in our Japanese and Chinese specimens of R. (s. str.) tamahumeralis. The male of R. (P.) himalayenis Chaudhuri & Sinharay, 1983 resembles those of R. (s. str.) effusus and R. (s. str.) tamahumeralis in the gonostylus with a roundly convex outer margin, and the mensural data. In R. (P.) himalayenis, the superior volsella looks extended posteriorly, beak-like, in the drawing by the authors (Chaudhuri & Sinharay 1983: 400 fig. 1f), which shows that the species belongs to the subgenus Rheocricotopus, not Psilocricotopus. Concerning R. (R.) effusus, Goetghebuer (1932: 59) wrote: “lobe anal à peine obtus”, and Lehmann (1969: 378) mentioned in the couplet 9 of the key for males: “Wings with a well-developed anal lobe (as in fig. 18a)”. Therefore, the male wing of R. (s. str.) himalayenis may be more similar to that of R. (s. str.) effusus with a nearly right-angled anal lobe, rather than that of R. (s. str.) tamahumeralis with an obtuse anal lobe. However, R. (s. str.) himalayenis cannot be confidently treated as a junior synonym of R. (s. str.) effusus, because the structure of humeral pit is not reported in the original description (Chaudhuri & Sinharay 1983: 398). Thus, R. (P.) himalayenis Chaudhuri & Sinharay is tentatively treated here as a junior synonym of R. (s. str.) effusus.

Published as part of Niitsuma, Hiromi & Tang, Hongqu, 2026, Taxonomic review of Rheocricotopus Brundin, 1956 (Diptera: Chironomidae: Orthocladiinae) from East Asia, with descriptions of twelve new species, pp. 1-114 in European Journal of Taxonomy 1037 on pages 83-84, DOI: 10.5852/ejt.2026.1037.3157, http://zenodo.org/record/18507203