Figs. 6–9, 64–68
Bythocsopus juglans Matsumura, 1912: 304 (synonymy by Okudera, 2014) Bythocsopus towadensis Matsumura, 1912: 304 (synonymy by Okudera, 2014) Oncopsis adusta Anufriev, 1967: 175 (synonymy by Hamilton, 1980)
Description. Male greenish yellow with strongly developed black pattern on face; vertex, pro- and mesonotum as a rule almost entirely black, forewings strongly infumose with transparent areas along claval suture, before end of clavus and on costal margin (Fig. 6). In weakly pigmented males and in females black pattern is more or less reduced (Figs. 7–8); lightest females are pale greenish yellow with small brown spots on head, pro- and mesonotum and with hardly distinguishable traces of dark pattern on forewings (Fig. 9).
Penis of typical shape, with ventral margin convex in side view (Figs. 64–65). Lower appendage of dorsal connective bent ventrally, with simple tip, smoothly curved or with blunt extension in the apical one third of dorsal margin. Apical third of dorsal margin finely serrated (Figs. 65–67). Style parallel-margined, with acute tip (Fig. 68).
Body length (including tegmina): ♂, 4.6–4.8 mm; ♀, 4.7–5.2 mm.
Differs from most other Russian species in coloration; in external appearance sometimes similar to O. furva, O. sepulcralis, and dark males of O. sulphurea (Figs. 1, 10–12, and 16–17). Distinctly differs from all known species by the shape of the lower appendage of dorsal connective.
Host. Alnus hirsuta on Southern Sakhalin, A. hirsuta and A. matsumurae in Japan (Okudera, 2014).
Distribution. Russia: Southern Sakhalin, Kurile Islands (Shikotan, Kunashir); Japan: Honshu (Hayashi & Higashikawa, 1997, as O. adusta; Okudera, 2014), Hokkaido, Shikoku (Okudera, 2014).