Thinobius bicolor Joy, 1911

(Figs 4, 16, 29–31)

Thinobius bicolor Joy, 1911: 10.

Thinobius linderianus Scheerpeltz, 1966: 257. (new synonym in Schülke & Makranczy 2011)

Examined type material – Thinobius bicolor Joy – Lectotype (♀), by present designation: “Type [red framed disc] \ Dalwhinnie; N.H.J. 1.5.[=V.][19]10 \ Brit. Mus.; 1924-468. \ Thinobius; bicolor. Joy; ♂ Type \ EMM 1911 \ bicolor Joy \ Lectotypus; Thinobius; bicolor Joy; des. Makranczy, 2003 / Thinobius; bicolor Joy; det. Makranczy, 2013” (BMNH); [For types of Thinobius linderianus, see Makranczy & Schülke, 2001: 189.].

Other material – GREAT BRITAIN: Scotland, Dumfries, River Nith, April 1870?, leg. D. Sharp (1255A) (1, coll. Champion, BMNH, 1, coll. Tottenham, BMNH); Harburn, near Carsfairs, April 23, 1866, leg. D. Sharp (1025) (10, BMNH); Ranvoch, May 2-9, 1866, leg. D. Sharp (1030) (1, BMNH, 1, coll. Sharp, BMNH); [Ranvoch?], May 1866, leg. D. Sharp (2, coll. Power, BMNH); Palmont [Polmont, Stirling], April 19-20, 1866 leg. D. Sharp (1023) (2, coll. Champion, BMNH, 3, coll. Sharp, BMNH), Gribton Bridge, April 30, 1868, leg. D. Sharp (1128) (1, coll. Sharp, BMNH), Seat at Druidhill near Eccles, May 11, 1869, leg. D. Sharp (1184) (1, coll. Sharp, BMNH); Dumfries, April 1867, leg. D. Sharp (1056] (1, coll. Sharp, BMNH); Cavin Water, May 1, 1867 leg. D. Sharp (1057) (1, coll. Sharp, BMNH); Morton Mains April 12, 1868 leg. D. Sharp (1123) (1, coll. Sharp, BMNH); Cumberland, Great Salkeld, 10.IV.1909, [leg.] H. Britten (1, coll. Champion, BMNH); Perthshire, Kinbuck [56.2213° N, 3.9481° W], 18.IV.1982, leg. R.M. Lyszkowski (2, HNHM); GERMANY: Rheinland, Nahe, Heinzenberg, Kellerbachtal, 19.IV.1988, leg. P. Wunderle (1 ♂, 1 ♀, HNHM).

Redescription – Measurements (in mm, n = 4): HW = 0.30 (0.295 –0.315); TW = 0.31 (0.305–0.33); PW = 0.32 (0.31–0.34); SW = 0.34 (0.32–0.35); AW = 0.40 (0.38–0.45); HL = 0.24 (0.24–0.25); EL = 0.08 (0.08–0.09); TL = 0.11 (0.10–0.12); PL = 0.26 (0.25–0.27); SL = 0.40 (0.38– 0.44); SC = 0.37 (0.34–0.41); FB = 0.92 (0.88–1.00); BL = 1.94 (1.72–2.15). Body (Fig. 4) in fully coloured specimens slightly bicoloured (see also remarks). Head, pronotum and abdomen dark brown. Elytra light to medium brown, scutellar area sometimes broadly darker. Legs, mouthparts and antennae light to medium brown, first two antennomeres somewhat lighter, terminal three segments often darker. All main body parts with very fine coriaceous microsculpture intermixed with punctation, making body moderately lustrous. Punctation very fine and rather dense, less distinct than in previous 3 species; head strongest, pronotum finer and more dense, abdomen similar but even less distinct, elytra hardly discrenible, surface dominated by microsculpture. Pubescence on forebody rather depressed, short, fine and dense (on elytra the most dense), on abdomen somewhat less dense and longer hairs, apices of tergites with a row of long hairs, abdominal sides and apex with a few darker and stronger bristles. Strong dark bristle on outer side of supraantennal tubercle at anterior border of eye and on posterior edge of vertex adjacent to temples, similar ones right behind anterior pronotal corner and on side at 3/5 length. Setation on head mostly medially directed, as also on pronotum but anterior on posterior pronotal edge and antero-medial on a smaller spot in middle hind part of disc. Elytra and abdomen with posteriorly directed hairs. Antennae, legs and mouthparts with very short, not conspicuous setation, except for the stiff, darker mid-tibial hairs ond ones near apices of femora. Sides of elytra with three such stiff setae about equally distributed on length of side.

Head slightly wider than long, temples usually somewhat widening then narrowing in a gentle curve, weakly rounded on posterior part. Middle of vertex with a slight transversal impression. Anterior border of neck is strongly marked with a shiny, arched, deep groove. Frontoclypeal suture appearing as fine, often shinier groove and dark line connecting supraantennal tubercles, similarly darker spots situated at both sides on middle of vertex. Supraantennal tubercles moderately developed, separated from vertex by longitudinal impression. Antennae medium long (Fig. 16), 6th antennomere appearing as wide as adjacent ones.

Pronotum weakly transverse, 1.30× wider than long, just a tiny bit wider than head, some very gentle impressions at side of unmarked pronotal midline especially in the middle of disc. Anterior corners rather weakly rounded, posterior corners very broadly, sides gently arched. Pronotal marginal bead visible on posterior and lateral margins, anterior margin slightly pulled ahead in middle with visible marginal bead. Scutellum small, if exposed, shinier than adjoining areas. Elytra rather long, one elytron about twice as long as broad, flat and parallel-sided (very gently dilating posteriorly). Shoulders moderately developed. Along suture without even traces of marginal bead; sutural corners moderately broadly rounded. Legs of medium length, tarsal lobes small and thin, inconspicuous, tibiae rather fusiform, appear much wider in middle than at ends.

Abdomen very weakly fusiform, sides more or less straight and parallel; widest in the middle, just very slightly less wide than elytra at broadest point. Posterior margin of tergite VII with palisade fringe and posterior corners broadly rounded. Primary and secondary sexual features: Sexes not appearing different in regular dorsal view. Posterior corners of tergite VIII (similar in both sexes) slightly pulled out, posterior edge gently concave, arched in between. Male sternite VIII as in Fig. 29, tergite IX as in Fig. 30, sternite IX as in Fig. 31.

Distribution – A very incompletely known species, mainly due to its difficult separation from Thinobius bunneipennis Kraatz, 1857, but seems to be present in the British Isles and Western Europe.

Remarks – The type of T. bicolor is a female and it belongs to a pair of sibling species (T. bicolor and T. brunneipennis) where females cannot be distinguished at the present state of our knowledge. To assure the correctness of the identification of this species, the whole historical British unidentified material in BMNH was checked. The males in this material, without exception, proved to belong to the taxon previously treated as T. linderianus (see Makranczy & Schülke 2001: 189). Therefore, it seems that the sibling taxon, T. brunneipennis (in the identity fixed by the neotype designation in the previously cited article) does not occur in Britain. As the valid name of the species is T. bicolor, a special note about the reliability of colour characters is felt in place here. It is very usual to have certain body parts lighter, brighter in fully coloured specimens, while teneral or not fully coloured specimens remain more or less unicolorous. A good example of this is a recently described species, T. gurzoeszterae Makranczy, 2009, where the female holotype (Fig. 55) is fully coloured with rather contrasting body parts, whereas the male paratype appears unicolorous. A similar situation exists with T. bicolor and T. brunneipennis, where specimens with bright elytra occasionally occur, but it is not true for all specimens and not linked to geographical distribution.