Mesoconius oblitus ( Hennig, 1935 ) Marshall, 2019

Marshall, Stephen A., 2019, A revision of the genus Mesoconius Enderlein (Diptera, Micropezidae, Taeniapterinae), European Journal of Taxonomy 548, pp. 1-126 : 111-115

Mesoconius oblitus ( Hennig, 1935) comb. nov.

Figs 45–46

Aristobata oblita Hennig, 1935: 32 .

Zelatractodes oblitus – Steyskal 1968: 20 .

Material examined

Holotype VENEZUELA • ♂; “Venezuela, 486, TYPUS”; dirty, missing right fore leg and left antenna; SMTD.

Paratypes (not examined)

VENEZUELA • 2 ♀♀; Merida; MLUH .

Other material

VENEZUELA • 1 ♂; Lara, PN Yacambú; 6–8 Apr. 1981; A.S. Menke and L. Hollenberg leg.; USNM • 1 ♀; Merida, Rio Albarregas ; 2200 m a.s.l.; 24 Apr. 1988; S.A. Marshall leg.; cloud forest; DEBU A305- 17 sequenced for CO1; DEBU .

COLOMBIA • 1 ♀; Huila, PNN Cueva de los Guácharos Cabaña Cedros ; 01°37ʹ N, 76°06ʹ W; 1950 m a.s.l.; 21 Dec. 2001 – 5 Jan. 2002; C. Cortes leg.; Malaise trap; MYCRO334-18 sequenced for CO1; IAVH .

Redescription

LENGTH. 15–17 mm.

COLOUR. Mostly brown to black, head darker, fore femur yellow basally, fore tarsus white, hind tarsus white basally and darkened distally (dirty and dark on type). Hind femur brightly banded but variable, yellow-brown at base, then black, then white band, then black, then yellow-brown at apex; mid femur similarly coloured on type but non-type specimens with a more orange mid femur ( Fig. 45B ). Scutum with a continuous, broad, parallel-sided, silvery longitudinal strip on each side of a central dark strip. Wing membrane lightly infuscated, except for a large central clear area in cell r 4+5. Abdominal pleuron pale.

HEAD. Epicephalon and paracephalon indistinctly striate, epicephalon with dense white microtrichosity. Frontal vitta conspicuously raised, with ocellar triangle on a distinct peak at centre of a prominent dome 0.6× as wide as frons, vitta sharply constricted behind ocelli, forming a short microtrichose trough not reaching postocellar bristles; vitta widely separated from anterior margin of frons. Lower frons and parafacials densely covered with white setulae. Palpus not clearly visible on type but very narrow, brown on other material. Postocellar bristles very closely spaced and slightly divergent, inner vertical bristle well developed. Two fronto-orbital bristles, widely separated, upper fronto-orbital bristle very large, inserted on epicephalon well above level of ocellar tubercle, lower fronto-orbital minute.

THORAX. Scutum densely microtrichose, with silver microtrichia forming two broad, longitudinal vittae separated by a gold strip of similar width; dorsocentral setulae forming a sparse row in silver vitta; acrostichal setulae forming a distinct row in central gold strip. Prosternum microtrichose and setulose. Cervical sclerite subquadrate, with a vertical groove separating a large microtrichose posterior section from a bare anterior portion. Postpronotal lobe sparsely microtrichose and very sparsely setulose. Dorsocentral bristle slightly longer than scutellum. Scutellum with minute discal setulae and one pair of long apical bristles (longer than scutellum). Vertical row of katepisternal bristles golden. Katatergite not swollen, without median process, evenly convex and microtrichose. All coxae with an anteroventral tuft of long golden setae.

ABDOMEN (based on non-type Venezuelan material). Segments 1–2 petiolate, narrow and twice as long as T3.

FEMALE ABDOMEN. Bursa with a small subquadrate body with a small ventral receptacle, distally extending as a broad common spermathecal duct. Single spermathecal duct arising just before apex of common spermathecal duct, uniformly smooth and parallel-sided until a constriction just before basally swollen and distally tapered single spermatheca. Paired spermathecal duct arising at apex of common duct, entirely smooth and uniform from apex of striated common duct to constriction before splitting into paired spermathecae and their stems. Paired spermathecae elongate-oval, not distinctly striate, stems narrow, distal section with an S-bend.

MALE ABDOMEN. Preabdominal sternites greatly reduced, but S4–6 present as distinct, elongate and very narrow sclerites. Sternite 8 subequal to epandrium, setulose except for bare posterior margin, partially fused with broad ventral lobe of S7 on left side, separate from a large lateral, normally invaginated sclerite on right side. Epandrium setulose, long-setose posterodorsally. Ejaculatory apodeme larger than epandrium; hypandrium with a long, scoop-like anterior margin, basal part of distiphallus broad, distally extending hood-like over a large phallic bulb; distal distiphallus slender and curved into flat, symmetrical, scoop-like anterior part of hypandrium.

Remarks

The specimens here treated as Mesoconius oblitus share many distinctive characters, including the unique and diagnostic prominent frontal tubercle, the characteristic bicoloured and white-banded femora, the microtrichosity of the epicephalon, the characteristically vittate scutum and the narrow brown palpus. This leaves little doubt that they are at least closely related, but the variation in other characters is hard to assess with so few specimens. The non-type male from Venezuela and the female from Colombia, for example, have much more orange on the femora than the type, and the Colombian specimen lacks the dark area proximal to the white femoral band. More specimens are needed to distinguish intraspecific variation from interspecific variation and to ascertain whether the material examined here represents one species or a group of related species. Sequence (barcode) data group the Colombian female with the Venezuelan female, but with a deep split between them.

The combination of a long distal distiphallus and a long, scoop-like anterior hypandrium is unusual and not found in other groups.

Figures

Fig. 45. Mesoconius oblitus (Hennig, 1935), external characters. A. Typical ♀, DEBU, Venezuela. B. Colour variant, ♂, USNM, Venezuela. C. Holotype, ♂, SMTD. D. Posterior part of thorax, lateral view. E. Head, ♀, DEBU, specimen from Venezuela. F. Head, ♀, IAVH, specimen from Colombia. G. Colour variant, ♀, IAVH, oviscape removed, specimen from Colombia.

Fig. 46. Mesoconius oblitus (Hennig, 1935), internal characters. A. Spermathecae and associated structures, specimen from Colombia. B. Male terminalia, left lateral view, specimen from Venezuela.