Tachydromia Meigen, 1803

Sicus Latreille, 1797: 158 . Type species: Musca cimicoides Fabricius, 1781, by subsequent designation of Latreille (1810: 443) [= Musca arrogans Linnaeus, 1761]. Preoccupied by Sicus Scopoli, 1763 [ Diptera, Conopidae].

Coryneta Meigen, 1800: 27 . Type species: Tachydromia connexa Meigen, 1822, by subsequent designation of Coquillett (1910: 528). Suppressed by I.C.Z.N., 1963: 339 (Opinion 678).

Tachydromia Meigen, 1803: 269 . Type species: Musca cimicoides Fabricius, sensu Curtis, 1833: pl. 477 (by designation of Curtis 1833), misidentification [= Tachydromia connexa Meigen, 1822].

Sicodus Rafinesque, 1815: 130 . Type species: Musca cimicoides Fabricius, 1781, automatic [= Musca arrogans Linnaeus, 1761]. Replacement name for Sicus Latreille, 1797 .

Danistes Gistel, 1848: XI. Type species: Musca cimicoides Fabricius, sensu Curtis, 1833, automatic [= Tachydromia connexa Meigen, 1822]. An unnecessary new name for Tachydromia Meigen, 1803 .

Phoneutisca Loew, 1863: 19 . Type species: Phoneutisca bimaculata Loew, 1863 (monotypy).

Tachista Loew, 1864a: 7, 15. Type species: Musca cimicoides: sensu Meigen, 1803, by subsequent designation of Coquillett (1903: 258), misidentification [= Tachydromia connexa Meigen, 1822].

Tachysta: authors, error or emendation.

Recognition. Tachydromia is distinguished from other Nearctic genera of the tribe Tachydromiini by the following combination of characters: veins CuA+CuP and CuA absent (cell cua absent); eye margins more or less divergent on vertex, occiput with scattered, fine setae on lower part; frons usually with nearly parallel sides; thorax with mesopleuron extensively shiny; vertical setae inclinate (sometimes slightly proclinate); wing membrane often banded.

Diagnosis. Usually small (1.5–2.5 mm, rarely 3–3.3 mm), brown to brownish black, shiny flies. Frons with nearly parallel sides, sometimes slightly broadened above (near anterior ocellus at most 1.5 times broader than near antennae). Eyes touching on face, almost touching on its middle portion or, sometimes, narrowly separated ( T. punctifera group). Vertical setae prominent, 1 pair, inclinate (sometimes slightly proclinate). Ocellar triangle with 1 pair of prominent setae.Antenna with postpedicel small, subglobular; stylus arising somewhat subapically, of varying length, with inconspicuous pubescence. Palpus varying in shape and length, sometimes bicoloured in male ( T. punctifera group). Thorax extensively shiny, proepisternum tomentose or shiny, mesoscutum sometimes tomentose (non-Nearctic species); postpronotal lobe elongate oval (length varying), postpronotal seta absent; mesoscutum usually 1.5–1.6 times longer than broad (sometimes 1.2–1.3 times); acrostichal setae absent. Fore femur and tibia thickened; mid leg more or less slender, in males often modified. Wings normally developed, of subequal width on basal and distal half; sometimes shortened (e.g., T. phengites) or very reduced (an undescribed species noted in illustrated key of Sinclair et al. (2023: 8, Couplet 2, figs a, b; 9, Couplet 3’, fig. a) as Tachyempis sp.), absent in some Palaearctic species; membrane often with brown cross-bands or macules (bands entirely separated or fused anteriorly). Rs originating before or near middle of R 1, length varying. Cell cua absent (veins CuA+CuP and CuA absent). Crossvein bm-m transverse; cell br distinctly shorter than cell bm at apex. Abdominal segments 1–7 with unmodified structure and vestiture. Male hypopygium small to moderately large; right epandrial lamella sometimes with small ventral projection bearing tuft of long flattened setae ( T. fuscinervis group); right surstylus separated or not separated ( T. halterata complex) from apex of epandrial lamella, sometimes bilobed; left surstylus barely separated from epandrial lamella; cerci separated, usually nearly digitiform and of subequal lengths, sometimes right cercus strongly reduced ( T. halterata complex).

Female usually similar to male but with unmodified structure and vestiture of mid leg; terminalia long; tergite 8 separated from sternite 8; cercus long, slender.

Remarks. Sometimes species of Tachydromia may be misidentified as Tachyempis Melander (and vice versa) due to an indistinct and somewhat confusing original definition of the latter genus (Melander 1928). More precise differences between Tachydromia and Tachyempis are given below. The re-definition of Tachyempis is discussed further in our forthcoming paper (Shamshev & Grootaert 2024). Although, the shape of the frons and the wing colour are not conclusive characters to distinguish Tachydromia and Tachyempis, they sometimes are useful for practical purposes.

1 Thorax with mesopleuron extensively shiny. Vertical setae inclinate (sometimes slightly proclinate). Frons usually with nearly parallel sides, but sometimes somewhat broadened above. Wing membrane often with cross-bands or maculae............................................................................................... Tachydromia Meigen

- Thorax with mesopleuron tomentose. Vertical setae lateroclinate. Frons often with sides relatively broadly divergent above, V-shaped to nearly Y-shaped. Wing membrane hyaline to more or less infuscate, very rarely banded.... Tachyempis Melander

Several groups of species were recognised within Tachydromia from the Palaearctic and Oriental regions (Shamshev & Grootaert 2018). Some of the Palaearctic groups can be revealed among described Nearctic species as well (see Discussion).