Megatrigon Johnson 1898
Creators: name: Doczkal, Dieter
name: Radenković, Snežana
name: Lyneborg, Leif
name: Pape, Thomas
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Syrphidae
Megatrigon

description: Key to species of Megatrigon
The currently known species are probably a fraction only of the species actually in existence, and users of the key should expect to encounter species that are not included. The key should be used mainly as a step in the identification process, and proper identification requires comparisons with the diagnoses and descriptions, including a thorough study of the terminalia. As the identification of females is still unresolved and/or the assignment to the corresponding males is uncertain, the key can be used for males only (except for the very distinct female of M. nivalis comb. nov.).
1. Katepisternum posteriorly setose over (almost) full width.Wing base extensively bare of microtrichia, esp. large parts of cells c, r 1, br, bm, and cup. The bare flat posterior margin of tergite 1 extensively microtrichiose. Thoracic setae not feathered but thickened and strongly glistening. ♂ terminalia with posterior surstyle lobe directed posteriorly, with a small hook at apex (Fig. 10M:y). ♀ tergite 5 and sternite 5 with anteriorly directed setae (Fig. 8 A–B), ovipositor with a subapical dorsal tooth (Fig. 8C) ………………………… nivalis group: M. nivalis (Hull, 1964) comb. nov. (Fig. 1M)
– Katepisternum either without setae between the dorsal and the ventral pile patches or with a few short setae below the dorsal patch. Wings either entirely microtrichiose or with small areas in cells br, bm, and/or cup bare of microtrichia.The bare flat posterior margin of tergite 1 (almost) bare of microtrichia. Thoracic setae serrate. ♂ terminalia with posterior surstyle lobe directed medially (Fig. 13B, F:y). ♀ tergite 5 and sternite 5 with posteriorly directed setae, ovipositor without a tooth ……2
2. Posterior surstyle lobe straight, without hook (Fig. 13E:y, F:y). Sternite 4 with inflated caudal lobes, each of which bears a small process on their median margin (usually visible only when the terminalia are extended), and with some part bare of microtrichia …………………………………………… sexfasciatus group [not treated here at the species level]
– Posterior surstyle lobe forming a strong twisted hook(Fig.13A:y,B:y).Sternite 4with flat caudal lobes, without process at median margin, and entirely covered by microtrichia ……………3 argenteus group
3. Tergites 2+3 with silver spots (Fig. 7 A–F), i.e., areas densely covered by adpressed reflecting white microtrichia. These spots cover the lateral part of the tergite for more than three quarters the length of the tergite ……………………………………………………………………………4
– Tergites 2+3 without silver spots (Fig. 7 G–K). Non-reflecting fasciae or spots of microtrichia are present, their maximum length less than half the length of the tergite, or all tergites without any markings ……………………………………………………………………………………………9
4. Costagial setae black. Ocellar triangle with a longitudinal groove. Mesofemur anteriorly black setose. Metatibia in proximal half dorsally with reduced microtrichia, not reaching scar. Tergite 4 with a pair of isolated submedian microtrichiose spots (Fig. 7A) ………………………………… …………………………………………………… M. argenteus (Walker, 1852) comb. nov. (Fig. 1A)
– Costagial setae yellow. Ocellar triangle without groove. Mesofemur without black setae. Metatibia in proximal half dorsally with a microtrichiose stripe that extends to the scar. Tergite 4 either without microtrichiose spots or present (M. sexmaculatus sp. nov.) anterolaterally……5
5. Tergite 4 with silver spots (Fig. 7F). Silver spots on tergite 3 completely and densely setose, setae directed towards the lateral margin, i.e., turned ca. 90° in relation to longitudinal axis. Vertex entirely microtrichiose except for a narrow stripe along the posterior margin (Fig. 2G) …… …………………………………………………………………… M. sexmaculatus sp. nov. (Fig. 1F)
– Tergite 4 without silver spots. Silver spots on tergite 3 for a large part without setae or (some M. magnicornis sp. nov.) with scattered setae, setae turned to the side for ca 45°. At least ocellar triangle partly bare of microtrichia ………………………………………………………………6
6. Postpedicel elongated (Fig. 3D). Vertex almost bare of microtrichia (Fig. 2D). Silver spots on tergite 3 widely separated, their distance exceeds the length of the tergite, narrowly separated from anterior and posterior margins (Fig. 7D). Tergite 3 with extensive areas with black setae …………………………………………………………………… M. magnicornis sp. nov. (Fig. 1D)
– Postpedicel normal. Vertex in front of anterior ocellus entirely densely microtrichiose. Silver spots on tergite 3 narrowly separated, their distance less than half the length of the tergite, covering whole length of tergite. Tergite 3 with or without a few scattered black setae ……………………7
7. Distance between eyes 0.17 × width of head, ocellar triangle isosceles (Fig. 2C). Larger species, body length about 8 mm ………………………………… M. argentimaculatus sp. nov. (Fig. 1C)
– Distance between eyes larger, ocellar triangle equilateral (as in Fig. 2F). Smaller species, body length 6.5–7.0 mm ………………………………………………………………8 (as in Fig. 1B, E)
8. Postocellar spot small, separated for about the distance between posterior ocelli (Fig. 2B). Median apex of the silver spot on tergite 2 near middle of tergite (Fig. 7B). Mesonotum with welldeveloped submedian and lateral (notopleuron, supraalar area) microtrichiose stripes ……… …………………………………………………………………… M. argentifrons sp. nov. (Fig. 1B)
– Postocellar spot large, almost confluent (Fig. 2E, F). Median apex of the silver spot on tergite 2 close to posterior margin of tergite (Fig. 7E). Mesonotum with traces only of the submedian and lateral microtrichiose stripes (Fig. 4B) …………………………………… M. natalensis sp. nov. (Fig. 1E)
9. Tergites without microtrichiose fasciae or spots (Fig. 7I). Distance between eyes big, frons and vertex with smooth surface (setae with simple alveoli, i.e., without tubercles), without microtrichia (Fig. 2J) …………………………………………… M. immaculatus sp. nov. (Fig. 1I)
– At least tergites 2+3 with microtrichiose fasciae or spots (as in Fig. 7K). Distance between eyes narrower, frons and vertex with rough surface (setae with tuberculate alveoli), with microtrichiose pattern at least on vertex (as in Fig. 2I) …………………………………………………………10
10. Postsutural pilosity of mesonotum black, with a intraalar microtrichiose stripe well separated from supraalar seta. Wing membrane brown along veins (Fig. 5C), posterior margin of alula bare of microtrichia. Tibiae 1–3 bright reddish, without dark rings ……… M. tabanoides sp. nov. (Fig. 1K)
– Mesonotal pilosity entirely light (white or yellow), with a supraalar microtrichiose stripe (as in Fig. 4C). Wing membrane either clear or completely infuscated, alula entirely microtrichiose. Tibia 1 and 2 each with a dark ring, tibia 3 almost completely blackish. ……………………………………11
11. Tergites 2+3 with widely separated microtrichiose fasciae, tergite 4 with fasciae narrowly separated (Fig. 7J). Vertex almost bare of microtrichia (the very few microtrichia do not form a distinct pattern) (Fig. 2K). Wing membrane light brown …… M. ochreatus (Hull, 1964) comb. nov. (Fig. 1J)
– Tergites 2–4 with fasciae (Fig. 7G, H). Vertex extensively densely microtrichiose (Fig. 2H, I). Wing membrane clear ……………………………………………………………………………………12
12. Wing with yellow veins, microtrichia equally dense and light (yellowish) on whole wing, appearing unicolorous (Fig. 5A). Frons, except for a stripe along the lunula, and vertex except for a narrow stripe at posterior edge entirely densely covered by yellowish microtrichia (Fig. 2H). Setae on all parts of the body golden. Tergites without black setae ……………… M. apiformis sp. nov. (Fig. 1G)
– Wing with brown veins, in proximal half densely covered by white microtrichia, in distal half with dark microtrichia, thereby wing appearing bicoloured (Fig. 5B). Nearly whole frons and a large posteromedian area on vertex without microtrichia (Fig. 2I). Tergites extensively black setose … …………………………………………………………………… M. cooksoni sp. nov. (Fig. 1H)
description: Published as part of Doczkal, Dieter, Radenković, Snežana, Lyneborg, Leif & Pape, Thomas, 2016, Taxonomic revision of the Afrotropical genus Megatrigon Johnson, 1898 (Diptera: Syrphidae), pp. 1-36 in European Journal of Taxonomy 238 on pages 29-33, DOI: 10.5852/ejt.2016.238, http://zenodo.org/record/3849874