Mesoconius nigrihumeralis, Marshall, S. A., 2015

Marshall, S. A., 2015, Mesoconius Enderlein (Diptera, Micropezidae, Taeniapterinae) of Central America, Zootaxa 3914 (5), pp. 525-540 : 534-536

Mesoconius nigrihumeralis new species

Figs. 4A–4G

Description. Length (antenna to wing tip) 15–16 mm. Color: Head black except for silvery parafacial, yellow palpus and yellow clypeus; thorax orange or mottled orange and yellow except for black prothorax, postpronotal lobe and most of notum between postpronotal lobes; foreleg with coxa and basal half of femur pale orange, distal half of femur and tibia black, tarsus white; mid and hind femora orange except for dark anteromedial patches or rings just beyond middle and usually a basal ring (rings very diffuse on some specimens), mid tibia, mid tarsus and hind tarsomeres 2–5 brown; hind tibia and tarsomere 1 pale. Abdominal tergites orange except for small (sometimes indistinct) dark posterolateral patches on T3 and T4, pleuron of female obfuscated on the only available specimen, pleuron of one male white with darker pigmentation on segment 3 (pleuron obscured on other specimens), male S8 and epandrium pale yellow. Oviscape orange.

Head: Epicephala and paracephalon smooth and shining with indistinct striate pattern, lower half of frons dull; frontal vitta velvety black, posteriorly narrow and extending to back of head as a very narrow tapered groove, main part widely separated from frons margin but with a narrow, velvety black median extension almost reaching frons margin. Outer vertical, inner vertical and postocellar bristles strong, postocellars closely spaced and far behind level of inner verticals. Two equally large fronto-orbital bristles both inserted on shining paracephalon; upper one inserted about midway between upper ocellus and eye; lower one inserted below level of anterior ocellus. Upper face bare, broadly convex. Palpus pale yellow.

Thorax: Cervical sclerite small, subquadrate, divided into a convex dark posterior part and a smaller pale anterior part, both parts microsetulose. Scutum not pruinose but microsetulose, with rows of small acrostichal and dorsocentral setulae; postpronotal lobe shining in anterior third, otherwise microtrichose with some scattered small setulae. Katatergite weakly convex. Vertical row of katepisternal bristles yellow. Fore coxa with an anteroventral tuft of golden bristles, similar bristles on other coxae. Hind femur slightly swollen in apical third (in contrast with Central American congeners).

Abdomen: Syntergite 1+2 very narrow basally, constriction between syntergites about half as wide as base of T3; length of T1+2 2.9 times as long as T3.

Female abdomen: Bursa copulatrix small and rugose; ventral receptacle large, apically finger-like; single and common spermathecal ducts arising separately from bursa, paired duct with short, broad and rugose basal part about as long as wide, otherwise smooth, parallel sided until a round swelling just before it splits into two very broad sinuate separate ducts leading to broad, cylindrical, reticulate-surfaced, paired spermathecae. Single spermathecal duct narrower, smooth and parallel sided, narrowed past rounded subapical swelling; single spermatheca small, distally swollen and basally tapered.

Male abdomen: Sternites 5 and 6 well developed, each with a pair of broad posterior lobes, those of S6 longsetose. Sternite 7 forming a narrow spatulate ventral lobe. Sternite 8 very large, twice as large as epandrium, bare except for scattered setulae. Epandrium microsetose and sparsely setulose; cercus very small. Hypandrium with a very broad anterior plate. Postgonites small, directed ventrally, with 3 small apical bristles. Basal part of distiphallus broadly tubular, gradually expanding to a large 2-chambered phallic bulb; distal part of phallic extended in to a short, tubular, trunk-like sclerotized distal distiphallus section terminating in a slightly flanged opening.

Type material (all INBC). Holotype (♂) and 1 paratype (♂): COSTA RICA. Cartago, Quebrada Segunda, Refugio Nacional Fauna Silvestre, Tapantí, 1250 m. iv.1992, R. Vargas. Other paratypes: COSTA RICA. San José, Moravia, Zurquí de Moravia, tower path, 1600 m. 24–31.v.2013, Malaise, project ZADBI (1 ♂); 20.x.2012, project ZADBI (1 ♀).

Etymology. The name refers to the black anterior notum, including the postpronotal lobe or "humerus".

Comments. The abrupt transition from a black head and anterior notum to an otherwise mostly orange body renders this species easy to recognize in the field. The short, sclerotized distal distiphallus tube is unlike any other Mesoconius . Several features, including the developed fourth and fifth male sternites and the full complement of bristles on the back of the head (inner and outer verticals, postocellars) are plesiomorphic relative to all other Central American Mesoconius species. The undifferentiated paired spermathecal duct is plesiomorphic relative to Central American congeners other than M. tigrinus .

Figures

FIGURE 4 A – G: Mesoconius nigrihumeralis. A, male; B, thorax – abdomen junction to show relatively flat katatergite; C, male; D, male terminalia, inverted to correspond with Fig. 4 E; E, male with ventral terminalia exposed; F, spermatheca and associated structures, lateral; G, head (right outer vertical missing). Abbreviations: BDP—basal distiphallus, PB—phallic bulb, BC—bursa copulatrix, DDP—distal distiphallus, IV—inner vertical, PO—postocellar, PD—paired spermathecal duct, SD—single spermathecal duct, SS—single spermatheca, VR—ventral receptacle.