Type material: Holotype ♂: [Japan] Yorii [36°06′N 139°10′E], Saitama /Honshu, 3-IX/ T. Nambu 1977// Dolichocolon ♂ / vicinum Mesn. /det. H. Shima, 2006 [BLKU]. Paratypes: 1 ♂, Japan, Kagoshima-city [31°34′N 130°32′E], Uearata-cho, 4.vi.1965, leg. A. Tanaka [identified as Dolichocolon vicinum Mesn. by H. Shima] [BLKU]. Korea: 1 ♂, Chungcheongbuk-do, Chungju [36°58′N 127°55′E], Jongmin-dong, from Recreational Forest, to Mt. Gyemyeongsan peak, 775 m, 3.vi.2004, leg. H.-W. Byun et al. [DLSYU]; 3 ♂♂, Gyeongsangnam-do, Changnyeong-gun, Daehap-myeon, near Woopo neup (swamp), 29.viii.2003, H.-Y. Han & K.-E. Ro [2, DLSYU; 1, MZUR].

Etymology: From the Latin adjective ‘ abstrusus, a, um ’, meaning hidden.

Description: Body length: 8.7–10.1 mm.

Coloration and pruinescence: Head mostly black with gena and anterior rim of parafacial reddish, covered with whitish-grey pruinescence. Palpus mainly brown or dark brown, shading into yellowish apically. Scape and pedicel black or dark brown (rarely brownish). Thorax mainly black; posterior 1/3–4/5 of scutellum reddish-yellow; postalar callus varying from yellow to black; scutum with four presutural dark vittae, lateral vitta distinctly outlined and ending wedgeshaped beside posthumeral seta. Legs black. Tegula and basicosta black or dark brown. Abdomen black, more or less reddish laterally on tergites 3 and 4; tergite 3 with a transverse band of whitish-grey pruinescence on anterior 1/3–1/2, tergite 4 pruinose on anterior 2/3–4/5, tergite 5 on anterior 1/2–4/5.

Head: Compound eye with short and very sparse ommatrichia at most as long as combined diameter of two facets (visible under> 60 ¥ magnification). Second aristomere about six to seven times as long as wide. Thickened part of third aristomere about 0.5–0.8 times as long as second aristomere. Postpedicel 6.3–6.5 times as long as pedicel. Vertex at its narrowest point 0.98–1.10 times as wide as compound eye in dorsal view. Lateral vertical seta only slightly differentiated from postocular setae. Six to eight frontal setae descending below level of base of arista. Fronto-orbital plate with one row of medioclinate setae or setulae lateral to row of frontal setae. Gena in profile 0.17–0.20 times as high as compound eye. Postocular setae fine, relatively long, slightly bent anteriorly. Prementum about 1.0–1.5 times as long as wide.

Abdomen: Syntergite 1 + 2 with short and weak median marginal setae. Tergite 3 with one pair of median marginal setae 0.5–0.8 times as long as corresponding tergite. Tergite 4 with a row of nine to 12 marginal setae. Tergite 5 with a row of marginal and discal setae.

Male terminalia (Fig. 15A–D): Epandrium short and convex. Basal 3/5–2/3 of cerci strongly prominent (Fig. 16C) and subrectangular in lateral view; distal 1/3–2/5 digitiform and strongly bent posteriorly (Fig. 16C). Laterobasal margin of cerci up-curved. Medial preapical tooth of cerci well developed, rounded. Surstylus, in lateral view, not bent posteriorly; slightly pointed in front distally, slanted anterodistally and covered with hook-like setae (Fig. 16A, B). Medial side of surstylus, in posterior view, membranous, subglobular (Fig. 16C, D).

Notes: Dolichocolon abstrusum was in the past confused with D. vicinum because of their external similarity. These two species, even though distinct and identifiable on the basis of the male terminalia, do not have sound external diagnostic characters. Therefore past data on the distribution of D. vicinum need careful revision. Not a single specimen of D. vicinum from Japan was examined during this study; hence, it is probable that citations for Japan (cf. Herting, 1984; Herting & Dely-Draskovits, 1993) should be referred to D. abstrusum sp. nov.

Hosts: Unknown.

Distribution: Palaearctic: Japan (Honshu, Kyushu), South Korea.