Key to species of the M. bicolor species-group

1 Postpronotal lobe with 3 setae........................................................................... 2

- Postpronotal lobe with 2 setae.......................................................................... 19

2 Stem vein setose dorsally (Fig. 489)...................................................................... 3

- Stem vein bare dorsally................................................................................ 4

3 Wing yellowish along costa; subcostal sclerite with pubescence only; male frons narrow, 0.01 of head width at narrowest; female T6 of FU shape (Fig. 314); [known only from Brazil].......................................... M. peregrina

- Wing with dark infuscation along costa (similar to Fig. 2); subcostal sclerite setose; male frons broader, 0.03–0.06 of head width at narrowest; female T 6 in WU shape (Fig. 304); [known from Argentina, Brazil, Ecuador, Paraguay, Peru; Marinho et al. (2017) also listed it from Bolivia, Colombia, French Guiana, Suriname and Venezuela]................ M. bellardiana

4 Wing with brownish to dark brown infuscation along costa (similar to Fig. 2)...................................... 5

- Wing hyaline (similar to Fig. 1) or yellowish (not brown) along costa; basal area of wing may be darkened............. 13

5 Abdomen with heavy whitish tomentum and dark pit-like spots around setal sockets (Fig. 103); epiphallus of normal length; hypophallic lobes broad and of elongate oval shape in dorsal view (Fig. 148); female T6 of WV shape (Fig. 303); [known from Brazil, Ecuador and Peru; Marinho et al. (2017) also listed it from Colombia, Trinidad and Venezuela]........... M. batesi

- Abdomen without heavy whitish tomentum or dark pit-like spots; epiphallus of variable length; hypophallic lobes not broad, elongate and oval in dorsal view......................................................................... 6

6 Supravibrissal setae bright orange; setae on subcostal sclerite, if present, bright orange.............................. 7

- Supravibrissal setae usually brown or black; if orange, then very dark not bright; setae on subcostal sclerite, if present, not orange.............................................................................................. 8

7 All legs reddish; wing with section IV 0.63 of section III; epiphallus of normal length (Fig. 187); hypophallic lobes very narrow in dorsal view (Fig. 188); [known only from Venezuela]..................................... M. velasquezae sp. nov.

- Mid and hind tibiae and tarsi black or dark brown; wing with section IV 0.82 of section III; epiphallus unusually short (Fig. 161); hypophallic lobes broad and pear-shaped in dorsal view (Fig. 162); [known from Brazil, Ecuador and Peru; Marinho et al. (2017) also listed it from Bolivia and Colombia].................................................. M. currani

8 A large fly (usually 16–17 mm); section IV of wing 0.50 of section III or more.................................... 9

- A small to medium-sized fly (8–12 mm); section IV of wing 0.35 of section III or less, except 0.44 in M. serrata ........ 10

9 Palpus yellow; discal scutellar setae present; section IV of wing 0.51 of section III; face dark; wing with veins in posterior half outlined with dark shading; epandrium, cerci and surstyli as in Figs 81–82; [known only from Bolivia; Marinho et al. (2017) also listed it from Colombia and Costa Rica]..................................................... M. pictipennis

- Palpus brown; discal scutellar setae absent; section IV of wing 0.75 of section III; face yellowish; wing veins in posterior half only faintly shaded; epandrium, cerci and surstyli illustrated in Guimar„es (1977: figs 70, 87); [known only from Colombia]......................................................................................... M. apollinaris

10 Wing with section IV more than 0.30 of section III; hypophallic lobes in dorsal view with distinctive coarse serrations (Figs 156, 180)........................................................................................... 11

- Wing with section IV less than 0.25 of section III; hypophallic lobes with finer serrations dorsally (Figs 178, 184)....... 12

11 Wing with dark infuscated area along costa to R 2+3; a larger fly, about 12 mm in length; mid and hind femora with basal 1/4 to 1/2 brown and apical half of lighter, yellow-orange color [slightly darker in one specimen]; ac usually 2:3 or 2:2; wing with section IV 0.31 of section III; epiphallus very short (Fig. 155); hypophallic lobes narrow in dorsal view (Fig. 156); female T6 of OV shape (Fig. 307), without suture midway; [known only from Bolivia and Peru]..................... M. brunnipes

- Distal 2/3 of wing faintly infuscated along costa; a smaller fly, around 9 mm in length; all femora entirely orange; ac 2:1; wing with section IV 0.44 of section III; epiphallus of normal length (Fig. 179); hypophallic lobes broad and pear-shaped in dorsal view (Fig. 180); female T6 of WV shape (Fig. 319), with suture midway; [known only from Peru]....... M. serrata sp. nov.

12 Tibiae and tarsi brown; abdomen with distinct oblique pale streaks of tomentum; ac usually 2:3; male frons 0.015 of head width at narrowest; female T6 of OV shape (Fig. 321); [known only from Brazil (Marinho et al. 2017), Peru and Bolivia]................................................................................................. M. townsendi

- Tibiae orange; abdomen with some pale tomentum, but not in oblique streaks; ac usually 2:1; male frons 0.063 of head width at narrowest; female T6 of WU shape (Fig. 318); [known only from Brazil]........................... M. semihyalina

13 Wing with distinct yellowish area along costa or entirely yellowed............................................. 14

- Wing usually hyaline or with very faint yellowing, primarily along costa........................................ 16

14 Subcostal sclerite bare; discs of upper and lower calypters pale; rim of upper calypter dark with pale setae, rim of lower calypter pale with long pale setae; wing with section IV 0.28 of section III; [widespread and common; Mexico and Central and South America except Argentina and Chile (Marinho et al. 2017)]............................................. M. bicolor

- Subcostal sclerite setose; wing section IV 0.45 or more of section III........................................... 15

15 Scutellum without discal setae; abdomen entirely shiny purple-blue; wing with heavy yellowing along costal margin, whole wing yellowish except cell r 4+5 with clear oval in middle; upper and lower calypters reddish; rim of upper calypter dark with short reddish setae, rim of lower calypter pale with long reddish setae; epandrium with fine dark setae (Fig. 95); phallus in dorsal view without curved horn-like structures projecting from sides of basiphallus; hypophallic lobes narrow (Fig. 186); female T6 of WV shape (Fig. 322); [widespread in Central America and northern South America].................. M. umbrosa

- Scutellum with discal setae; abdomen bluish, with heavy whitish tomentum and dark pit-like areas around setal sockets (similar to Fig. 103); wing mostly hyaline, with yellow area only along costa; upper and lower calypters pale; rim of upper calypter slightly darkened, with short pale setae, rim of lower calypter pale with long pale setae; epandrium with stout black setae (Figs 69–70); phallus in dorsal view with long curved posterior directed horn-like structures projecting from sides of basiphallus; hypophallic lobes broad and oval-shaped (Fig. 160); female T6 of RV shape (Fig. 309); [known from French Guiana and Brazil].................................................................................... M. chantryi sp. nov.

16 Postpronotal lobe and femora orange..................................................................... 17

- Postpronotal lobe and femora bluish..................................................................... 18

17 Subcostal sclerite setose; thorax with 2:2 or 2:3 ac, 1 ia, kat 2:1; male frons 0.08 of head width at narrowest; male T3 a triangle of bluish cuticle from hind margin to point in middle of tergite (Fig. 493); surstylus and cercus robust (Figs 91–92); epiphallus normal (Fig. 181); female T6 of OV shape; [known from Central America and northern South America]......... M. socors

- Subcostal sclerite bare; thorax with 2:1 ac, 0 ia, kat 1:1; male frons 0.025 of head width at narrowest; T3 without a triangle of bluish cuticle on hind margin; surstylus and cercus slender (Figs 75–76); epiphallus very short (Fig. 165); female T6 of in WV shape (Fig. 312); [known from Costa Rica and Panama]............................................. M. flavicrura

18 T5 with dense, irregular, long and slender setae; kat 2:1; male frons 0.04 of head width at narrowest; epandrium, cerci and surstyli distinctive: surstylus long and straight in lateral view, cercus even longer and also straight (Fig. 77); in posterior view, surstyli much shorter than cerci and apically curved outward, basal two-thirds of cerci narrow, parallel-sided (Fig. 78); phallus in dorsal view exceptionally narrow (Fig. 168). Female T6 of OV shape (Fig. 313); [known only from Bolivia]............................................................................................. M. longicercus sp. nov.

- T5 with shorter, sparser setae; kat 1:1; male frons broader, 0.09 of head width at narrowest; epandrium, cerci and surstyli in lateral view with surstylus very short, slightly curved backward, and cerci much longer than surstyli (Fig. 67); in posterior view, basal half of cerci bulbous, apical half abruptly narrowing to tip (Fig. 68); phallus in dorsal view broader (Fig. 158); female T6 of RV shape (Fig. 308); [known only from Bolivia]............................................ M. bullata sp. nov.

19 Wing entirely hyaline; male frons narrow, 0.06 of head width at narrowest; female T6 of WV shape (Fig. 305); [known from French Guiana, Guyana, Peru and Venezuela; Marinho et al. (2017) also listed it from Brazil]................. M. benoisti

- Wing with more or less dark infuscation along costa; male frons broader, 0.08–0.12 of head width at narrowest.......... 20

20 Wing with weak infuscation along costa; T1+2–T4 with bluish-purple horizontal bands on posterior margins (best seen in well-preserved specimens); ac 0:2; rim of upper calypter sooty; female T6 of OV shape (Fig. 311); [known only from Brazil; Marinho et al. (2017) also listed it from Colombia].............................................. M. cyaneicincta

- Wing with dark infuscation along costa; T1+2-T4 without horizontal bands on posterior margin; ac 0:1; rim of upper calypter light or dark........................................................................................ 21

21 T4 with complete row of marginal setae; posthumeral seta absent; upper calypter with pale rim; male frons 0.10 of head width at narrowest; female T6 of WV shape; T7 narrowed midway (Fig. 316); [known from Bolivia, Brazil, Guyana, Peru and Venezuela; Marinho et al. (2017) also listed it from Colombia and Venezuela]........................... M. quadrilineata

- T4 without row of marginal setae; posthumeral seta present, sometimes small; upper calypter with dark rim; male frons narrower, 0.08 of head width at narrowest; female T6 of FU shape; T7 broad midway (Fig. 317); [known from Bolivia, Brazil, Guyana and Peru].............................................................................. M. randa