Amplisegmentum Webb, 2005

Winterton, Shaun L., 2021, A new species of Amplisegmentum Webb (Diptera: Therevidae) from Venezuela, Zootaxa 4927 (4), pp. 576-582 : 576-577

Amplisegmentum Webb

Amplisegmentum Webb, 2005: 4 .

Type species: Amplisegmentum ecuadorensis Webb, 2005: 4 .— Gaimari & Webb (2009) [key]; Webb et al. (2013) [catalogue]; Irwin & Winterton (2020) [key].

Diagnosis. Male frons wider than anterior ocellus; scape bulbous; flagellum turbinate to conical; prosternum with setal pile; scutellum with two pairs of macrosetae; wing cell m 3 open; head thorax and abdomen with extensive elongate admixed white lanceolate and black filiform setae; inner gonocoxal process present; gonocoxites separate medially.

Description. Head. Antennal length equal to head length; flagellum turbinate; flagellum shorter than combined scape and pedicel length; scape bulbous, noticeably thicker than pedicel and base of flagellum; frons only slightly raised around base of antennae, antennae positioned in middle of head and directed anteriorly; head length and height subequal; gena rounded; male frons width (at narrowest point) equal to or wider than anterior ocellus; parafacial with or without setae along eye margin; male postocular macrosetae scattered medially on occiput and concentrated in one row (dorsally) along postocular ridge. Thorax with central depression of prosternum setose; pleuron overlain with dense silver or grey pubescence admixed with pale erect setae; metanepisternum with postspiracular setae present; metakatepisternum with setae absent; scutal chaetotaxy (pairs): supra alar, 1–2; post alar, 1; dorsocentral, 2 or 0; scutellar, 2; posterior surface of midcoxa without setae or sometimes just a few setae; midfemoral vestiture as dark, erect filiform seta admixed with pale lanceolate and adpressed scale-like setae; fore- and midfemora anteroventral macrosetae present or absent, present on hind femur as a series along length, all femora with posteroventral macrosetae absent or indistinct; hind femur and tibia approximately equal length to fore and mid legs; hind coxal knob present; wing cell m 3 open, veins M 3 and M 4 separate to margin; wing vein R 2+3 smoothly sigmoid to wing margin, wing mostly hyaline or with faint markings present; wing vein R 1 with setae absent distally. Abdomen. Extensive pile of white lanceolate setae on all segments; male with silver velutinous pubescence. Genitalia ( Fig. 4 ). Male with epandrium and gonocoxites with extensive pale, lanceolate setae; gonocoxite with gonocoxal process very small with 1–3 large, dark posterolaterally directed setae; inner gonocoxal process present; gonocoxite with posteromedial margins proximal but not fused; ventral lobe large, elongate to rounded; hypoproct (subepandrial sclerite) small or absent; dorsal apodeme of phallus broad; distiphallus narrow, straight or directed ventrally; ventral apodeme narrow. Female with acanthophorite macrosetae well developed (A1 & A2); sternite 8 posterior margin emarginate posteromedially; two spherical spermathecae with thickened spermathecal ducts basally; spermathecal sac rounded.

Comments. The original circumscription of the genus by Webb (2005b) was based on a single species ( A. ecuadorensis ), which is here revised to accommodate the new species and correct some inaccuracies in the original description. Amplisegmentum is easily differentiated from other Therevinae by the following characteristics: antennal scape bulbous; scattered dark macrosetae on the male occiput (in addition to a distinct dorsal row); wing cell m 3 open; prosternum setose medially; metanepisternum with setal patch; two pairs of scutellar macrosetae; posterior surface of mid coxa with, at most, just a couple of setae present. The male gonocoxites are mostly covered in white lanceolate setae, but with a small raised outer gonocoxal process with 2–4 large black macrosetae. This condition is also found in the closely related Notiothereva ( Webb, 2005a) and while it is common in Therevidae to have enlarged posterolateral macrosetae on the gonocoxites, it is distinctive here as they are in stark contrast to the abundant white lanceolate setae. Amplisegmentum can be specifically separated from Notiothereva by the presence of scattered macrosetae on the occiput in both sexes (single postocular row in male of Notiothereva ), bulbous scape (narrow cylindrical in Notiothereva ), mid coxae largely lacking setae (present in Notiothereva ) and male eyes separated medially by at least the width of the anterior ocellus (contiguous medially below the medial ocellus in Notiothereva ). Note that Webb (2005b) described that the wing cell m 3 is closed in Amplisegmentum , but it is open in both species ( Fig. 4 ). In addition, the male occiput is described as consisting of a single row of postocular black macrosetae in Webb (2015b), but there are also black macrosetae scattered medially on the occiput, similar to the condition found in A. venezuelensis sp. n.

Included species. Amplisegmentum ecuadorensis Webb ; A. venezuelensis sp. n.

Figures

FIGURE 4. Amplisegmentum venezuelensis sp. n., male genitalia.A. epandrium; B. gonocoxites, ventral view; C. same, lateral view; D. phallus, lateral view; E. same, dorsal view. Scale line: 0.2 mm. Abbreviations: d, distiphallus; da, dorsal apodeme of parameral sheath; ea, ejaculatory apodeme; gs, gonostylus; igp, inner gonocoxal process; vl, ventral lobe.