Tachydromia chelana Melander

Shamshev, Igor V. & Grootaert, Patrick, 2024, Revision of the described Nearctic species of the genus Tachydromia Meigen (Diptera: Hybotidae), Zootaxa 5403 (2), pp. 151-196 : 159-161

Tachydromia chelana Melander

( Fig. 4 )

Tachydromia chelana Melander, 1928: 282 . Type locality: USA, Stehekin, at head of Lake Chelan , Washington.

Notes on type series. Melander (1928) described T. chelana from the female sex only (two specimens taken from “ Stehekin, at the head of Lake Chelan, Washington ”). We have not examined the type material of this species.

Material examined. NORTH AMERICA. CANADA. Northwest Territories: Tuktoyaktuk , 15.vii.1971, W. R. M. Mason (1 ♂, CNC) ; Inuvik , 68°22´N 133°45´W, MT, shore of E Branch Mackenzie River, H. Goulet & C. Boudreault (1 ♂, 1 ♀, CNC) ; Inuvik , 68°22′N 133°45′W, 23 m, sweeping, meadow, 9.vii.2010, H. Goulet & C. Boudreault (1 ♀, CNC) . USA. Alaska: Nome area, mi. 17 of Kougarok Road , 64°42′N 165°17′W, Malaise, 20–26.vi.2005, J. & A. Skevington (1 ♂, CNC) . EURASIA. RUSSIA. Sakha (Yakutia) Republic: Ajakit , 30.vii.1875, Czekanowski (1 ♀, ZISP) ; Chokurdakh, swampy floodplain of river Indigirka , 7.viii.1972, Gorodkov (1 ♂, 4 ♀, ZISP) ; same locality, 20.viii.1971, Gorodkov (1 ♀, ZISP) ; Uryung-Khaya , 5.viii.1988, Gorodkov (1 ♀, ZISP) ; Nizhneyansk , shrub tundra, 31.vii.1974, Gorodkov (1 ♂, ZISP) ; river Koyverelan , 63°05′N 173°00′E, 200 m, 28.vii.1959, Gorodkov (1 ♂, ZISP) .

Diagnosis. The species is distinguished by the following combination of characters: palpus without black subapical seta; proepisternum mostly pruinose. Male: palpus narrowed towards apex, mostly pale yellow, narrowly brownish at apex; mid tibia with 2 closely set, long subapical setae posteriorly. Female: palpus uniformly pale yellow.

Redescription. Male (described for first time, Fig. 4A ). Length: body 2.1–2.4 mm, wing 2.3–2.5 mm. Head black. Occiput (including posterior portion of vertex) densely greyish pruinose, shiny only behind mouth-opening; 2 short, black vertical setae. Ocellar triangle shiny; ocellars slightly shorter and finer than verticals. Frons shiny, nearly parallel-sided, above antennae 2.0–2.5 times as broad as anterior ocellus. Antenna with scape and pedicel yellow, postpedicel and stylus brown. Postpedicel subglobular; stylus subapical, 2.0–2.5 times as long as pedicel and postpedicel combined. Proboscis blackish brown. Palpus nearly as long as proboscis, not divided into two lobes apically, somewhat narrowed towards apex; mostly pale yellow, narrowly brownish at apex; covered with scattered, pale, fine short setae, lacking black subapical seta.

Thorax black, largely shiny, main setae black; prosternum, proepisternum (except narrow upper part) and meron near lower margin densely whitish grey tomentose; notopleural depression along lower margin, scutellum and postnotum greyish tomentose. Postpronotal lobe large, elongate oval, lacking conspicuous setae, with scattered minute setulae. Mesonotum with 1 long notopleural, 1 shorter postalar and 4 subequally long scutellars (sometimes 6); some minute setulae present behind postpronotal lobe and on notopleural depression anteriorly; acrostichals absent; dorsocentrals uniserial, mostly minute, 1 prescutellar pair long (nearly as long as postalar seta).

Leg colour: fore coxa yellow, mid and hind coxae brownish to yellowish brown; fore and mid femora mostly yellow, somewhat brownish subapically and dorsally, hind femur entirely brown; tibiae almost entirely brown, yellow near extreme base; tarsi largely brownish, mid and hind tarsomeres brownish yellow on basal part. Fore coxa clothed in numerous pale setae and densely silvery grey tomentose anteriorly, mid and hind coxae with patch of similar tomentosity laterally. Fore femur thickened; whitish pubescent ventrally; with rows of mostly minute, fine anteroventral and posteroventral setae becoming longer closer to base of femur (anteroventral setae slightly longer; 3–4 moderately long setae in each row near base); some fine setae near base posteriorly. Fore tibia mostly strongly thickened, spindle-shaped; with row of slightly stronger setulae ventrally. Mid femur slender, unmodified; bearing rows of mostly minute anteroventral and posteroventral setae becoming moderately long and stronger closer to base of femur (latter somewhat longer near base including 1 longest basalmost seta). Mid tibia lacking apical projection, with 2 rows of stronger ventral setulae on apical part, bearing 2–3 short, ventral subapical setae and 2 closely set long setae posteriorly. Hind femur unmodified, with short anteroventral setae. Hind tibia and tarsus unmodified.

Wing normally developed, rounded at apex, with unmodified venation; with two brownish, entirely separated bands, distinct on about anterior half of wing and hardly distinguishable posteriorly. One very short costal seta present. Vein R 2+3 straight or slightly undulate, thickened and strongly turned towards costa subapically (sometimes with short subapical appendix). Veins R 4+5 and M 1+2 nearly parallel. Crossveins r-m and bm-m broadly separated. Cell r 1 slightly broader than cells r 2+3 and r 4+5. Calypter brownish, with somewhat paler fringe. Halter with brownish stem and pale yellow knob.

Abdomen brown to blackish brown, pregenital segments unmodified (except segment 8); mostly shiny, with scattered minute setae; tergites 7–8 rather subshiny, faintly pruinose; segments 7–8 with longer posteromarginal setae.

Hypopygium ( Fig. 4B–D ) black, small, elongate oval. Right epandrial lamella subtriangular (lateral view), with several unmodified moderately long setae apically, lacking additional lobes ventrally. Right surstylus ( Fig. 4C ) separated from epandrial lamella; small, subrectangular (lateral view), bent inwards, with several submarginal spinules. Left epandrial lamella ( Fig. 4D ) small, with several unmodified moderately long setae. Left surstylus barely separated from epandrial lobe; elongate, broadly ovate apically, with several unmodified, moderately long setae. Hypandrium with 2 minute setulae. Cerci ( Fig. 4B ) separated, elongate ovate, of subequal lengths, left cercus slightly broader; with some unmodified moderately long setae. Hypoproct subtriangular viewed dorsally, produced nearly to apex of right cercus.

Female. Palpus uniformly pale yellow to whitish. Fore and mid femora usually darker, more brownish. Mid femur with thinner setae closer to base; mid tibia lacking subapical setae. Otherwise as in male. Abdominal segment 6 shiny; segment 7 mostly pruinose, narrowly shiny laterally; visible parts of segment 8 pruinose. Cercus brownish, long, slender, with minute setulae.

Remarks. Shamshev (2016) synonymised T. chelana with T. incompleta (Becker) that is not followed herein after an examination of new material (primary from Asiatic part of Russia). The specimens mentioned above agree with Melander’s description of T. chelana in almost all characters (except somewhat paler legs). This identification should be validated in the future by an examination of the type material.

It is evident from the original description that T. chelana belongs to the T. punctifera group of species sensu Chvála (1975) because Melander notes “ribbon-like, white palpi without subapical seta”. This group includes T. bimaculata , T. incompleta (Becker) , T. punctifera (Becker) and T. tacoma Melander , which all are present in North America. Tachydromia chelana is very similar to T. incompleta differing by broader pruinose occiput and by tomentose lower portion of the proepisternum. In addition, in the male of T. chelana the palpus is somewhat narrowed apically (sometimes pointed) and is only narrowly brownish at apex (see the key). Tachydromia chelana and T. incompleta are hardly distinguishable based on the male terminalia. In addition, the female of T. chelana resembles the female of T. bimaculata . However, the latter species has pale setae on the mesonotum.

Distribution. Holarctic. North America: Canada (Northwest Territories), USA (Alaska, Washington); Eurasia (first record): Russia (Yakutia).

Figures

FIGURE 4. Tachydromia chelana Melander, male (Canada, Northwest Territories; CNC). A. Habitus, lateral view. B. Hypopygium,dorsal view.C. Right surstylus, lateral view.D. Left epandrial lamella andleft surstylus, lateral view.Abbreviations: cerc—cercus; lft sur—left surstylus; rt sur—right surstylus. B–D: scale bar is 0.1 mm.