Tachydromia varipennis Coquillett, 1903

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 : 189-191

Tachydromia varipennis Coquillett

( Fig. 18 )

Tachydromia varipennis Coquillett, 1903: 266 . Type locality: USA, New Hampshire, Franconia .

Notes on type series. Coquillett (1903) noted the following material: “A specimen of each sex, collected at Franconia, N.H., by Mrs. Annie T. Slosson. Type.—No. 6774, U. S. National Museum.”

Type material examined. SYNTYPES: ♂, FRANCONIA, N.H. // Mrs Slossen Collector // Type No 6774 U.S. N.M. [red label] // Tachydromia varipennis Coq. [hand-written] ; ♀ [glued on same plate with male] ( USNM) .

Additional material examined. CANADA. Manitoba: 6 mi. NW Brandon , 1.vii.1958, R . B. Madge (1 ♀, CNC) . USA. North Carolina: Highlands , 3800’, 3.vi.1957, J. R . Vockeroth (10 ♀, CNC) . Virginia: Stony Creek , Giles Co., 2000’, 26.v.1962, J. R . Vockeroth (2 ♂, 5 ♀, CNC) . West Virginia: High hills near shore, Md. n.e. Magnolia , 12.vii.1914, R . S. Shannon (1 ♂, USNM) .

Diagnosis. The species is distinguished by the following combination of characters: vertex faintly greyish pruinose on posterior portion; antennae brownish; prothoracic sclerites (except postpronotal lobe) densely whitish grey tomentose; legs with fore and mid femora yellowish; wing with two brownish, distinct bands connected across cells r 1 and r 2+3.

Redescription. Male ( Fig. 18A ). Length: body 1.7–1.8 mm, wing 1.8 mm. Head black. Occiput largely greyish pruinose, shiny below neck; vertex faintly pruinose (often with very narrow, more or less distinct, shiny patch on middle) behind ocellar tubercle; 2 inclinate, short, black, rather fine vertical setae; some pale setae around neck and near mouth-opening; row of short black postoculars on upper part. Ocellar triangle shiny; ocellars short, nearly as long as postverticals, lateroclinate. Frons shiny, slightly broadened towards ocellar tubercle; above antennae nearly 2.0 times as broad as anterior ocellus. Antenna brownish to yellowish brown (sometimes scape and pedicel somewhat paler). Postpedicel subglobular; stylus subapical, long. Proboscis brown. Palpus unmodified, slender, long, somewhat shorter than proboscis, whitish; clothed in numerous long silvery setae, with 1 short (nearly half as long as palpus) black subapical seta.

Thorax black, mostly shiny; prothoracic sclerites (except postpronotal lobe) densely whitish grey tomentose, meron with narrow space of similar tomentosity posteriorly; scutellum and postnotum faintly tomentose. Postpronotal lobe large, elongate oval, lacking conspicuous setae, with scattered minute setulae. Mesonotum with 1 black, moderately long notopleural, 1 shorter postalar and 4 scutellars (cruciate apical pair nearly as long as postalar seta, laterals shorter); some minute setulae present behind postpronotal lobe and on notopleural depression anteriorly; acrostichals lacking; dorsocentrals uniserial, numerous, mostly minute, 1 prescutellar pair nearly as long as scutellar apical setae.

Leg colour: coxae yellow to brownish yellow (mid coxa usually somewhat darker), fore and mid femora yellow (usually somewhat darker on subapical part dorsally), hind femur almost entirely brown, yellow near extreme base; tibiae brown (except yellow extreme base); basitarsi yellow (sometimes slightly darkened at tip), tarsomere 2 mostly yellowish (brownish apically), tarsomere 3 mostly brown (yellowish near base), tarsomeres 4–5 brown. Fore coxa clothed in numerous, short, pale hair-like setae; fore coxa anteriorly, mid and hind coxae laterally whitish pruinose. Fore femur strongly thickened, pubescent ventrally, with minute anteroventral and posteroventral pale setulae becoming longer closer to base. Fore tibia spindle-shaped, with unmodified setation. Mid femur slender, with 4–5 very short, brownish yellow setae near base anteroventrally; row of 8–9 somewhat longer, spinule-like, blackish setae on about basal half (paler closer to base of femur). Mid tibia with short apical projection, bearing ventral spinule-like setulae. Hind leg unmodified, lacking prominent setae.

Wing normally developed, rounded at apex, with unmodified venation; membrane with two brownish, distinct bands connected on cells r 1 and r 2+3, leaving base (except extreme basal portion) and apex of wing whitish hyaline; hyaline patch between bands reaching from near posterior margin to R 4+5. One short basal costal seta present. Vein R 2+3 straight. Veins R 4+5 and M 1 parallel near wing apex. Crossveins r-m and bm-m broadly separated. Calypter brownish, with scattered fringe. Halter with pale knob and brownish yellow stem.

Abdomen brownish; tergites narrowly faintly pruinose anteriorly and shiny posteriorly; tergites 6–7 (viewed dorsolaterally) entirely faintly pruinose; sternites faintly pruinose, covered with scattered setulae longer on pregenital segment.

Hypopygium ( Fig. 18B–D ) small, elongate oval, blackish brown. Epandrium mostly pruinose; right surstylus shiny; visible part of hypandrium shiny. Right epandrial lamella rather subtriangular viewed laterally, bearing unmodified, mostly moderately long setae apically (submarginal setae longer); without ventral projection or lobe. Right surstylus ( Fig. 18C ) separated from epandrial lamella, undivided; rather small, subtriangular, with rounded apex; bearing marginal, spinule-like setae. Left epandrial lamella ( Fig. 18D ) small, with short setae apically. Left surstylus not separated from epandrial lamella, elongate oval, with long setae. Cerci ( Fig. 18B ) separated, with unmodified short setae; right cercus digitiform, short; left cercus digitiform, nearly as long as but slightly narrower towards apex than right cercus. Hypoproct slightly produced beyond apices of cerci.

Female. Mid femur whitish pubescent ventrally, with pale anteroventral and posteroventral setulae. Mid tibia with slightly prominent apical projection. Otherwise as in male. Abdominal segments 6–8 and all sternites entirely greyish pruinose. Cercus brownish, long, slender, with minute setulae.

Remarks. Tachydromia varipennis can be readily distinguished from all described Nearctic species by the wing pattern, which includes two brownish bands connected across cells r 1 and r 2+3. However, this character is present in several Palaearctic species. Tachydromia varipennis is very similar to T. vladimiri Shamshev ( Mongolia) and, especially, to T. tuvinica Shamshev (south of Eastern Siberia) and T. kerzhneri Shamshev (south of the Russian Far East) ( Shamshev 1994b, 1994c). Tachydromia vladimiri differs from T. varipennis primarily by dark brown palpi and pruinose ocellar tubercle. Tachydromia kerzhneri and T. tuvinica differ from T. varipennis by the following characters: antenna with scape and pedicel yellow; postpronotal lobe pruinose along outer side; male abdominal tergites 6–7 shiny, epandrium covered with scattered short setae; female mid femur without whitish pubescence ventrally, bearing rows of dark anteroventral and posteroventral setulae. In addition, in T. tuvinica the median hyaline space of the wing is less distinct and present only on cell m1 (sometimes extending slightly beyond vein M 1).

Distribution. Canada (Manitoba); USA (Maryland, New Hampshire, North Carolina,? Oregon, Virginia,? Washington, West Virginia). Records of this species from Oregon and Washington, presented by Melander (1965) require confirmation.

Figures

FIGURE 18. Tachydromia varipennis Coquillett, male (USA, Virginia; CNC). A. Habitus, lateral view. B. Hypopygium, dorsal view. C. Right surstylus, lateral view. D. Left epandrial lamella and left surstylus, lateral view.Abbreviations: cerc—cercus; lft sur—left surstylus; rt sur—right surstylus. B–D: scale bar is 0.1 mm.