Marbenia Malloch

Ale-Rocha, Rosaly, Freitas, Geovânia & Mathis, Wayne N., 2014, Revision of the Neotropical genus Marbenia Malloch (Diptera: Periscelididae), Zootaxa 3872 (4), pp. 365-375 : 366-367

Marbenia Malloch

Marbenia Malloch, 1931: 31 . Type species: M. peculiaris Malloch, 1931 by original designation. Prado, 1975: 1 –3 (Neotropical catalog); Mathis & Rung, 2011: 350, 352 (world catalog).

Diagnosis. Small flies, body length 2.6–3.5 mm; maxillary palpus short and spatulate; setae of head elongate, postocellar pair well developed; face lacking setae, only a pair of setae on the facial plate, with transverse furrows giving face a wavy appearance; parafacial, gena and occiput with many strong setae; arista bipectinate; two pairs of dorsocentral setae; wing banded; R1 with dorsal setae; R2+3 long and arcuate; M1 almost straight; bm-cu complete; CuA2 lacking; A1+CuA2 extended nearly to wing margin; abdominal tergites 1+2 fused laterally.

Redescription. Body length: 2.6–3.5 mm. Head. Frons with parallel or slightly divergent margins anteriorly and slightly divergent on vertex; face lacking setae, only a pair of setae on the facial plate, internal to the genal row of setae, with transversal furrows giving face a wavy appearance; fronto-orbital plate with series of short setae below fronto-orbital seta; parafacial with well-developed setae, becoming longer and more robust toward ventral region. Buccal structures: palpus flat, short and spatulate, setose on distal half; clypeus U-shaped, microtomentose. Antenna: scape short; pedicel cap-like with dorsal cleft; first flagellomere elongate oval; arista bipectinate with dorsal and ventral rays decreasing progressively in length toward apex intercalated by some shorter rays. All setae conspicuous; ocellar triangle not setulose, ocellar pair well developed; postocellar setae developed and divergent; medial and lateral vertical setae well developed; 1 fronto-orbital long and reclinate. Gena and occiput with many strong setae. Thorax robust, approximately as wide as long (scutellum excluded); subscutellum protuberant; scutum covered with short setae, scutum and scutellum covered with dense pruinescence; 1 postpronotal, 2 notopleural, 1 postsutural supra-alar, 1 postalar, 2 postsutural dorsocentral, 1–3 katepisternal and 2 pairs of scutellar setae. Wing banded; subcosta incomplete; R1 with setulae on dorsal surface; R2+3 long and arcuate; M1 almost straight; M1 and CuA1 extended to wing margin; CuA2 lacking; A1+CuA2 extended nearly to wing margin; cell dm with longitudinal fold. Legs robust; mid tibia with 1 black apicoventral spine; mid tarsus with small black apical spines on ventral surface. Abdomen rather broad, covered by short setae and sparse pruinescence. Tergite 1+2 fused, with transverse unsclerotized region in the middle and longitudinal weak line dividing tergite medially up to membranous area. Male terminalia: symmetrical; sternite 6 well developed, tergite 6 slender; pregenital sclerite (syntergosternite 7+8) reduced to dorsolateral narrow stripe, free from tergite 6 or partially fused with tergite 6, and including spiracle 7; epandrium convex; surstylus undifferentiated; postgonites articulated at anterior margin of hypandrium, partly encircling base of phallus; cercus developed and setose; phallus long, ribbon-like; genital pouch (hypandrium + phallapodeme) large, inflated, slightly sclerotized, forming a bursa-like chamber containing the phallus; hypandrial arms long and fused anteriorly around base of phallus. Female terminalia: tergite 7 and sternite 7 fused, forming a complete ring; tergite 8 and sternite 8 free; sternite 8 broad, slightly concave on anterior margin; tergite 8 convex; cercus small, rounded.

Remarks. The relationships among Periscelidinae genera remain largely unsubstantiated. Ale-Rocha & Freitas (2011) suggested that Marbenia and Neoscutops are closely related based on one putative synapomorphy, vein R1 setulose dorsally. This character state is unique to Marbenia and Neoscutops , and conveniently distinguishes them from other genera in the subfamily Periscelidinae. Marbenia can be distinguished from Neoscutops by two characters: 2 postsutural dorsocentral setae (absent in Neoscutops ); veins R2+3 and M1 almost straight (R2+3 and M1 distinctly curved in Neoscutops ).

Geographical distribution. Neotropical ( Bolivia, Brazil, Ecuador, Panama).