Megatrigon nivalis ( Hull, 1964 ) Doczkal & Radenković & Lyneborg & Pape, 2016

Doczkal, Dieter, Radenković, Snežana, Lyneborg, Leif & Pape, Thomas, 2016, Taxonomic revision of the Afrotropical genus Megatrigon Johnson, 1898 (Diptera: Syrphidae), European Journal of Taxonomy 238, pp. 1-36 : 5-11

publication ID	https://doi.org/ 10.5852/ejt.2016.238
DOI	https://doi.org/10.5281/zenodo.3854670
persistent identifier	https://treatment.plazi.org/id/03EA327E-FFE5-EC1D-FD89-EEC8FE53FA3F
treatment provided by	Valdenar
scientific name	Megatrigon nivalis ( Hull, 1964 )
status	comb. nov.

Treatment

Megatrigon nivalis ( Hull, 1964) , comb. nov.

Figs 1M View Fig , 2N View Fig , 3M View Fig , 4D View Fig , 8 View Fig , 10M View Fig , 11 View Fig M–N, 12L, 16

Eumerus nivalis Hull, 1964: 485 View in CoL . Type locality: South Africa, Northern Cape, Belmont.

Diagnosis

See diagnosis of nivalis group.

Type material SOUTH AFRICA: ♁, holotype, Northern Cape, Belmont, 23 Feb. 1934, J. Ogilvie (BMNH). [Examined.]

The holotype is in bad condition, with both metalegs and right mesoleg missing (all from femur on), head glued to the thorax, left mesoleg soaked in an unknown substance.

Additional material

NAMIBIA: 1 ♁, Rundu, 31 Jan. 1993, leg. M. Schwarz (coll. M. Hauser); 1 ♀, same locality, 22 Jan. 1993, leg. J. Gusenleitner (coll. M. Hauser).

Description

LENGTH. Body 11 mm (♁), 12 mm (♀); wing 6.7 mm (♁), 7.3 mm (♀).

HEAD ( Figs 2N View Fig , 3M View Fig ). Face completely densely microtrichiose, only the slightly produced anterior mouth edge and a small area posterior to lateral mouth corner bare of microtrichia. Frons with a dense silver pilosity. Distance between eyes small (0.11 × width of head). Vertical triangle microtrichiose except for between and posterior to the posterior ocelli, postocellar spot small, microtrichiose very narrowly continuing along parasagittal sulci, postocular orbit behind postocular ridge with sparse microtrichia. Postocular area wide, about 1.5 × as wide behind dorsal eye corner than at the narrowest point on ventral half. Posterior eye margin slightly bent anteriorly dorsal to vortex. An ill-defined median furrow on vertex from posterior ocelli to posterior border. Ocellar triangle isosceles. Antenna black, base of

arista bright orange. Pedicel slightly elongate, postpedicel small, oval, sensory pit elongated, forming an oblique slit.

THORAX ( Fig. 4D View Fig ). Mesoscutum extensively and densely microtrichiose: median and submedian stripes extending to the level of wing base (the submedian stripes missing in female, Fig. 4D View Fig ), notopleuron, supraalar area, prescutellar area, transverse suture (the latter incomplete in female, Fig. 4D View Fig ). Scutal pilosity short, semi-decumbent, light (whitish), supraalar setae uniserial (with few extraserial setae), yellow. Notal wing process microtrichiose. Capitulum blackish. Setae on anterior part of anepisternum restricted to posterodorsal half. Proepimeron with long setae. Thoracic pleura bare of microtrichia on posterior part of anepisternum, on katepisternum anterior to the setose parts, and all of meron (lower part dulled by a fine surface sculpture). Protarsus shorter than protibia, stout; tarsomere 1 about as long as wide. Profemur and protibia reddish brown will ill-defined blackened parts, densely microtrichiose posteriorly and dorsally (obscuring surface), thinly microtrichiose anteriorly and ventrally, pilosity white. Tarsomeres 2–5 darkened dorsally.

WING. Costagium with yellow setae, posterior setae short (about as long as diameter of costa distal to costagium). Cells c, r 1, bm, cup and anal lobe with large areas bare of microtrichia, as well as narrow bare stripes along parts of the veins and at the posterior margin of the wing including alula, veins yellowish brown at base, darker brown towards apex.

ABDOMEN ( Fig. 8 View Fig ). Conical [similar to Merodon avidus (Rossi, 1790) ], lateral margins of tergite 2 convergent posteriorly, tergite 3 is 2 × as wide as long, tergite 2 with a median fascia, tergites 3+4 each microtrichiose anteriorly and with a median fascia, tergite 4 with microtrichiose posterior margin. Tergite 2 posteromedially (posterior to fascia) with a large triangular black setose area, most part of tergite 3 (except for fascia and lateral margins) black setose, tergite 4 with small black setose area between anterior and median fascia, otherwise tergites with whitish pilosity. Except for the lateral margin setae are very short, those on posterior margin of tergite 2 not distinctly exceeding margin of tergite, tergites pitted (alveoli). Genital pouch wider than half width of tergite 4 anteriorly. Sternite 1 large. Sternites 2–4 with semi-decumbent, comparatively short, white setae.

Distribution

Afrotropical – Namibia, South Africa ( Fig. 16 View Fig ).

argenteus group

Diagnosis

Katepisternum with a posterodorsal and a weak (composed of a few setae only) posteroventral pile patch, without setae between them. The bare flat posterior margin of tergite 1 (almost) entirely without microtrichia. Base of wing entirely microtrichiose or at most with small bare areas in cells br, bm, or cup. Anepisternal setae saw-like. Protarsomere 1 anterodorsally with a line of minute black spinules (yellow in M. argentimaculatus sp. nov. and M. tabanoides sp. nov.) between the yellow trichia.

♁: sternite 4 with flat caudal lobes, entirely microtrichiose. Genital pouch less than half as wide as abdominal segment 4 at anterior margin. Posterior surstyle lobe directed medially, its apex forming a strong twisted hook ( Fig. 13A View Fig :y). Median surstyle lobe setose along ventral margin on full length, on median surface extensively covered by microtrichia and posteriorly with a small inner accessory lobe pointing medially ( Fig. 13D View Fig :x). Cerci ( Fig. 10 View Fig :z) with blunt apex, ventral surface membraneous and without setae. Subepandrial sclerite strongly curved (in lateral view, Fig. 10 View Fig :w), and its anterior end sclerotized at the sides only, sclerotized but translucent in the middle, posterior part with a strongly trichiose pillow-like structure, which is densely furnished by unusually long and thick microtrichia ( Fig. 13C, D View Fig :z), otherwise bare. Hypandrium ( Fig. 12 View Fig :A–J) with a moderately wide base (in ventral view), without ‘shoulders’ between wide base and narrower distal half, apex distinctly produced beyond ctenidium and pointed. Ejaculatory apodeme small. The male terminalia of all included species are very similar ( Figs 10–12 View Fig View Fig View Fig ), the significance of the observed small differences between species needs to be proved by more material.

♀: tergite 5 and sternite 5 with posteriorly directed setae, ovipositor with moderately thick setae, without tooth.

The argenteus group can be subdivided into two subgroups, at least the first being monophyletic. A full description is given for M. argenteus comb. nov., which is the only fairly common species of this group (all others being rare or known from singletons only). The descriptions of the remaining species focus on the differences to M. argenteus .

Subgroup 1

Male tergites 2+3 flattened and with ‘silver spots’ (= patches of very dense silvery reflecting microtrichia) (not present in ♀).