Mesoconius hemithorax Frey

Marshall, S. A., 2015, Mesoconius Enderlein (Diptera, Micropezidae, Taeniapterinae) of Central America, Zootaxa 3914 (5), pp. 525-540 : 532-534

Mesoconius hemithorax Frey

Figs. 3A–3G

Mesoconius hemithorax Frey, 1927: 73 ; Hennig, 1935: 36.

Redescription. Size (antenna to wing tip) 16–18 mm. Color: Most of thoracic pleuron and leg bases dull yellow to orange; anterodorsal portion of propleuron, cervical sclerites, head (except labellum) and notum black to dark brown with distinct areas of silvery pollinosity; abdominal tergites brown with posterolateral corners of T2–5 darker, S8 and epandrium mostly pale brown to yellow. Fore coxa black anteriorly, yellow posteriorly. Fore femur yellow in basal 2/3 except for a longitudinal black anterodorsal stripe; distal third of femur and all of tibia black; tarsomeres yellow. Mid and hind femur orange with a broad, irregular distal black band and an elongate, black anterodorsal marking proximally (proximal and distal dark areas coalesced on some specimens); mid tibia orange–brown, darker distally; mid tarsus black; hind tibia and tarsus orange to yellow. Abdominal pleuron yellow except for prominent triangular black stripes tapering ventrad from lateral tergal membranes, giving abdomen a conspicuous zebra-striped appearance (more conspicuous in females than males).

Head: Epicephalon and paracephalon shining, with a dense but indistinct pattern of microscopic longitudinal striations; epicephala separated by the very narrow posterior extension of frontal vitta; orbits rugose and shining; frontal vitta pruinose, tapered to dorsal and ventral points, dark part of frontal vitta widely separated from anterior edge of frons but broad pruinose silvery anterior margin reaching anterior edge as a narrow strip. Postocellar and inner vertical bristle well developed, outer vertical bristle absent; upper fronto-orbital inserted above level of ocelli; 1–2 minute lower fronto-orbital bristles. Upper face bare, broad with a weak central carina; parafacials, gena, postgena and lateral margin of lower face strongly silvery pruinose, subantennal areas shining. Palpus pale yellow.

Thorax: Cervical sclerite divided into a convex, dark, microsetulose posterior part and a smaller pale, bare anterior part. Scutum with pruinose pattern of 4 silvery patches as noted above, otherwise unevenly microsetulose with a central sparsely microsetulose strip flanked by rows of small acrostichal setulae; dorsocentral setulae sparse. Katatergite very prominent, with a long, tapered nipple-like central process. Postpronotal lobe shining, with fine setae along outer margin only. Vertical row of katepisternal bristles brown, other katepisternal bristles including long ventral bristles pale. Fore coxa with an anteroventral tuft of mixed golden and black (mostly black) bristles; similar bristles on other coxae.

Abdomen: Syntergite 1+2 very narrow basally, constriction between syntergites about half as wide as base of T3; length of T1+2 double length of T3.

Female abdomen: Bursa copulatrix broad, quadrate, rugose, with single and double spermathecal ducts arising separately from a truncate distal margin; ventral receptacle very small, finger-like. Single spermathecal duct half as long and one third as broad as double spermathecal duct, smooth, ending in small, slightly swollen spermatheca; double spermathecal duct broad and conspicuously rugose over basal 3/4, distal quarter narrower and smooth, apically split into two ducts, each with a large oval swelling followed by a deep S-bend and a large cup-shaped spermatheca.

Male abdomen: Sternites 1–5 very narrow, S5 unmodified, almost linear; S6 pale, setulose and broadly rounded. Sternite 7 with a dark ventral and left lateral linear band; fused broadly with the large, unmodified S8. Epandrium with short anteroventral arms (1/5 of epandrial length); ventral part of epandrium strongly incurved. Hypandrium frame-like, anterior margin quadrate, posterior margin looping up over aedeagal apodeme, meeting epandrial arms, and extending posteriorly as an aedeagal sheath dorsally and a pair of pregonites ventrally; pregonites finely setulose with a prominent ventral lobe. Ejaculatory and aedeagal apodemes both large, with broad posterior parts; central body of sperm pump with finely spinulose surface. Basiphallus very small, frame-like; postgonites small, with inconspicuous setae; basal part of distiphallus broadly cylindrical, expanding distally to a cup-like phallic bulb; distal part of distiphallus very long and whip-like with multiple folds.

Type material. Holotype (unique, ♀, MZHF): PANAMA. “Lino, Fassl” [the collector was presumably the German entomologist Anton Heinrich Hermann Fassl (1876–1922), who made significant collections of various orders around Lino, Panama at about 800m)].

Other material examined ( INBC unless otherwise indicated): COSTA RICA. Alajuela, Volcán Tenorio, N slope, trail to laguna, 1000 m. rain forest, 16–20.vi.2000, S.A Marshall (2 ♂, 1 ♀, DEBU); Alajuela, San Ramón, Alberto Brenes Biological Reserve, 900 m. ii–iii.2000, P. Hanson (1 ♀). Cartago, Rio Grande de Orosí, Administración to La Pava trail, 1150–1600 m. iv.1997, R. Guzman (1 ♀). Guanacaste, Volcán Cacao, Cerro Pedregal, 1000 m. ii–iv.1989, I. Gauld (1 ♀). Puntarenas, Monteverde Biological Station, along upper trail, 10°18’7”N 84°48’10”W, 1700 m. 14–18.viii.2010, S.A. Marshall (1 ♂, DEBU); Puntarenas, San Luis, Monteverde, 1040 m. 1–31.x.1993, Z. Fuentes (1 ♂).

Comments. This species is similar in color to Mesoconius tigrinus , but the two-part paired spermathecal duct, the prominent katatergite, the very long distal distiphallus, and the head chaetotaxy suggest that M. hemithorax is more closely related to Andean species than to M. tigrinus .