Tachydromia tacoma 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 : 187-189

Tachydromia tacoma Melander

( Fig. 17 )

Tachydromia tacoma Melander, 1928: 281 . Type localities: USA, “ Mount Rainier, Washington ”, “ Moscow Mountain , Idaho ”.

Notes on type series. Melander (1928) noted the following material: “Many specimens from Mount Rainier, Washington, collected by Messrs. Dyar and Caudell and by the author, and one specimen from Moscow Mountain, Idaho ”. The syntypes are present in USNM, CNC and OUMNH.

Type material examined. SYNTYPES: ♀, Mt. Rainier , WN, Paradise Park, Aug. 1921, A.L. Melander; [redlabel] // Paratype, Tachydromia Tacoma Melander No. 1479 [yellow label] // Syntype, Tachydromia tacoma Mel. CNC No. 1479 ; ♀, same data and labels as in previous syntype, but collected on August 1917 ( CNC) .

Additional material examined. USA. Washington: Mt. Rainier, Yakima Park , 19.viii.1934, A.L. Melander (3 ♂, 2 ♀, USNM) .

Diagnosis. This species is distinguished by lack of black subapical seta on the palpus and by the following additional characters: Male: palpus bicoloured, black and bilobate apically; mid femur thickened, with broad excavation near base; mid tibia with subapical excavation. Female: palpus brown.

Redescription. Male ( Fig. 17A ). Body 2.9–3.2 mm; wing 3.0– 3.1 mm. Head black. Occiput largely densely greyish pruinose, broadly shiny only behind mouth-opening; scattered, black short setae on upper part and more numerous, longer, pale hair-like setae near neck laterally and on lower part; 2 strong, rather short, closely set verticals. Frons narrow, shiny, almost parallel-sided. Ocellar triangle subshiny, faintly pruinose, ocellars minute. Antenna with postpedicel and stylus brown, scape and pedicel somewhat paler, yellowish brown; postpedicel small, subglobular; stylus subapical, rather short. Proboscis brown, long, nearly half as long as head is high. Palpus modified, longer than proboscis; very narrow and yellow on basal part; broadened, black, shiny and bilobate on apical part; covered with scattered, minute setulae.

Thorax black, almost entirely shiny, with black setation; prothoracic sclerites (except antepronotum and postpronotal lobe), anterior margin of anepisternum, posterior part of meron and metapleuron densely silvery grey tomentose; antepronotum, posterior part of notopleural depression and postalar tubercle, scutellum and postnotum faintly brownish tomentose. Postpronotal lobe with several minute setulae. Mesonotum with 1 short, strong notopleural, 1 similar postalar and 4 scutellars (apical pair somewhat longer than notopleurals, lateral pair short).

Legs almost entirely brown, only femora near extreme apex, “knees”, tibiae on extreme base and basitarsi (except apex) yellowish. Fore coxa anteriorly, mid and hind coxae laterally densely silvery grey tomentose; fore coxa with cluster of several yellowish subapical setae; mid coxa with several similar setae on outer side; hind trochanter with some spinules dorsally. Fore femur thickened, shiny dorsally, densely silvery grey pruinose ventrally, with rows of pale anteroventral and posteroventral setulae. Fore tibia spindle-shaped, with row of short ventral black spinules. Mid femur thickened, viewed dorsally somewhat stouter than fore femur; faintly pruinose dorsally and on subapical part ventrally; large, shallow excavation closer to base; armed with row of about 8 long, strong anteroventral setae along margin of excavation and complete row of strong posteroventral setae becoming longer towards base. Mid tibia with very large, deep subapical excavation forming large, thumb-like posteromarginal projection, armed with numerous marginal spinules. Hind legs slender (including femur), subshiny, unmodified, with inconspicuous setation. Tarsi of all legs unmodified, with inconspicuous setation.

Wing normally developed; with two broad brownish bands darker anteriorly and connected in cell r 1. Short basal costal seta present. Vein R 2+3 sinuous; deeply concave towards costa, rather strongly turned at apex. Veins R 4+5 and M 1 nearly parallel near wing apex. Crossveins r-m and bm-m broadly separated. Calypter brown, with yellowish brown hair-like setae. Halter yellow knob and brownish yellow stem.

Abdomen black; tergites faintly greyish pruinose anteriorly, shiny posteriorly (except tergites 7 and 8), with scattered, brownish, short setulae; sternites shiny, with similar, denser setation; sternites 7 and 8 with longer posteromarginal setae.

Hypopygium ( Fig. 17B–D ) brown, moderately large; right epandrial lamella largely shiny, left epandrial lamella faintly pruinose. Right epandrial lamella rather subtriangular viewed laterally, bearing long, fine setae apically; without ventral projection or lobe. Right surstylus ( Fig. 17C ) separated from epandrial lamella, undivided; rather small, subtriangular, with rounded apex; covered with moderately long, fine setae, bearing marginal spinules. Left epandrial lamella ( Fig. 17D ) small, with short fine setae apically. Left surstylus not separated from epandrial lamella, elongate, narrow, with numerous long fine setae. Cerci ( Fig. 17B ) separated, digitiform; with numerous long, fine setae; right cercus moderately long; left cercus slightly shorter than right cercus. Hypoproct not produced beyond apices of cerci.

Female. Palpus ( Fig. 17E ) entirely brown, very narrow, strip-like, nearly as long as proboscis. Fore coxa with uniformly spread pale setulae. Mid femur slightly narrower than fore femur, lacking basal excavation, densely whitish pubescent ventrally, shiny posteriorly, otherwise faintly pruinose; rows of blackish, short anteroventral and posteroventral setae, former prominent throughout, latter inconspicuous near base. Mid tibia slender, lacking subapical excavation, with row of ventral spinules. Otherwise as in male. Abdominal terminal segments entirely pruinose. Cercus brown, with scattered setulae.

Remarks. Tachydromia tacoma belongs to the T. punctifera group sensu Chvála (1975).This species differs from all other members of the group by the brown palpus of the female. In addition, the male has a curiously modified mid leg. Tachydromia tacoma is one of the largest species of the genus in North America (together with T. enecator ).

Distribution. USA (Idaho, Washington).

Figures

FIGURE 17. Tachydromia tacoma Melander (USA, Washington;USNM).A–D. Male. A. Habitus,lateral view.B. Hypopygium, dorsal view. C. Right surstylus, lateral view. D. Left epandrial lamella and left surstylus, lateral view. E. Female head, lateral view. Abbreviations: cerc—cercus; lft sur—left surstylus; rt sur—right surstylus. B–D: scale bar is 0.1 mm.