Megatrigon argenteus ( Walker, 1852 ) 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 : 11-15

publication ID	https://doi.org/ 10.5852/ejt.2016.238
DOI	https://doi.org/10.5281/zenodo.3854650
persistent identifier	https://treatment.plazi.org/id/03EA327E-FFEB-EC19-FE6E-EF96FCF4F8FD
treatment provided by	Valdenar
scientific name	Megatrigon argenteus ( Walker, 1852 )
status	comb. nov.

Treatment

Megatrigon argenteus ( Walker, 1852) comb. nov.

Figs 1A View Fig , 2A View Fig , 3A View Fig , 7A View Fig , 9 View Fig , 10A View Fig , 11A View Fig , 12A View Fig , 13 View Fig A–C, 14, 15

Eumerus argenteus Walker, 1852: 224 View in CoL . Type locality: South Africa, Western Cape, Cape of Good Hope. Eumerus quadrimaculatus Macquart, 1855: 111 View in CoL . Type locality: South Africa, Western Cape, Cape of Good Hope.

Diagnosis

Costagial setae black. Ocellar triangle with a shallow longitudinal groove. Mesofemur anteriorly black setose. Metatibia in proximal half dorsally with reduced microtrichia, not reaching scar. Silver spots on tergite 3 are 1.4 × as wide as long; tergite 4 with a pair of isolated submedian microtrichiose spots ( Figs 1A View Fig , 7A View Fig ).

Type material

SOUTH AFRICA: ♁, holotype of argenteus [not ♀ as given by Walker]: “ Cape ” ( BMNH). [Examined by Nigel Wyatt.]

SOUTH AFRICA: ♁, holotype of quadrimaculatus [not ♀ as given by Macquart]. “ Eumerus /4- maculatus / ♀. Macq.” (original Macquart label), “ E. quadrimaculatus /ex. Coll. Bigot” (non-original label) ( UMO). Macquart (1855: 111) states “Cap de Bonne Espérance” as the type locality. [Examined.]

Additional material

SOUTH AFRICA: 2 ♁♁, Western Cape, Het Kruis, Oct. 1947, Mus. Exp. ( SAMC); 3 ♁♁, Western Cape, Paleisheuwel, Nov. 1948, Mus. Exp. ( SAMC); 2 ♁♁, Western Cape, Olifants River between Citrusdal and Clanwilliam, Oct.–Nov. 1931, Museum staff leg. ( SAMC); 1 ♁, Western Cape, Citrusdal, Nov. 1948, Mus. Exp. ( SAMC); 2 ♁♁, Western Cape, 24 km S of Vanrhynsdorp, 3 Nov. 1991, J.G.H. Londt leg. ( NMSA); 1 ♁, Western Cape, 2 km NW of Darling, 4 Oct. 1994, R. Danielsson leg. ( MZLU); 1 ♁, Western Cape, Cederberg, 21 km S of Clanwilliam, 22 Nov. 2002, W. Barkemeyer leg. (coll. Bkm); 1 ♁, Cape, Nuwekloof 3 km E of Gouda, 33°19ʹ S, 19°06ʹ E, 120 m, 5 Oct. 993, J.G.H. Londt leg. ( NMSA); 2 ♁♁, “Du Soils Kloof C. Thorne” 1 Apr. 1934 <?> ( SAMC; one without abdomen); 3 ♁♁, 1 ♀, 6 exuviae ( SAMC; no data).

MALAWI: 1 ♁, Kasungu Nat. Park, Lifupa Camp, 1333Aa, 1000 m, 9–10 Dec. 1980, Stuckenberg & Londt leg., Brachystegia ( NMSA).

Description

LENGTH. Body 7.0–11.0 mm, wing 5.0– 6.5 mm.

HEAD ( Figs 2A View Fig , 3A View Fig ). Ellipsoidal in frontal view (about 1.3 × as wide as deep); in lateral view about 1.5 × as deep as long; dichoptic eyes, distance between eyes relatively small, 0.13–0.14 × width of head; cuticle of head capsule brown-metallic bronze, shiny; face covered with long white setae; shiny, except narrow, short microtrichiose stripes along eye margins (missing in lower part), and median facial stripe wide below antennae (in some specimens connected with microtrichia along eye margin) and then tapering towards mouth edge; the width of face 0.37–0.38 × width of head; frons with semi-erect yellow setae, cuticle well visible, shiny; sometimes with reduced stripes of microtrichia near the eye margins; vertex covered with long, dark yellow setae (sometimes dark brown); shiny in the central part, but microtrichiose anteriorly (around front ocellus), laterally, along the eye margin, postocellar microtrichiose spots relatively small, separated by the distance between posterior ocelli; the width of vertical triangle 0.22–0.25 × width of head; microtrichia on post-ocular orbit dense, dorsally narrowly exceed postocular ridge and connected with postocellar microtrichiose spots, postocular orbit dorsally only little wider than at its narrowest part, 0.08 × width of head; ocellar triangle almost isosceles; with median longitudinal groove; antenna ( Fig. 3A View Fig ) brown, sometimes pedicel paler (orange brown) than postpedicel or end of pedicel and beginning of pospedicel paler (orange brown); setae on scape and pedicel predominantly white, except brown setae on dorsal part; postpedicel ellipsoidal, about 1.5 × as long as deep; 1.7–1.8 × as long as pedicel.

THORAX. Scutum black, laterally with golden lustre, anteriorly on median part dark blue, covered with moderately long, mostly relatively dense, (semi) erect yellow hairs, sparse on the blue anteromedian area; two lateral white microtrichiose stripes reaching the posterior end of scutum, two submedian microtrichiose stripes extending close after the transverse suture (occassionally almost absent) and more or less visible microtrichia on transverse suture, some specimens with a little trace of median microtrichiose stripe. Supra-alar setae usually black, inserted on enlarged tuberculate alveoli. Proepimeron covered with dense microtrichia and short, sparse, yellow setae. Anepisternum, anterior anepimeron, posterodorsal and ventral part of katepisternum, metasternum covered with long, yellow hairs. Microtrichia reduced or missed on median part of anepimeron, and a large spot on katepimeron (barrette). Scutellum black, with yellow rim; setosity of long yellow setae. Mediotergite mostly shiny, only median 0.25–0.33 of width sparsely covered with microtrichia.

WING. Membrane slightly brown infuscated, with brown veins and dark, dense microtrichia; at least proximal half of cell br largely without microtrichia; setae on costagium black; halter with yellow pedicel and capitulum.

LEGS. Brown, except light brown-orange on following parts: trochanters (more or less), proximal and distal part of pro- and mesofemur, large part of pro- and mesotibia (except weak submedian dark ring), proximal half and apex of metatibia, pro- (sometimes tarsomere 1 darkened dorsally) and mesotarsus and ventral surface of metatarsus (sometimes also tarsomeres 2–5). Hairs on legs predominately light yellow, long, except some short black setae on anterior and dorsal part of pro- and mesofemur, darkened setae on antero-ventral part of mesotibia and tarsi dorsally (especially metatarsus). White microtrichia distinct on pro- and mesofemur (very dense posteriorly, more inconspicuous on remaining parts), pro- and mesotibia dorsally, proximal 0.33 of metatibia dorsally (i.e., reduced compared with other species).

ABDOMEN ( Figs 1A View Fig , 7A View Fig , 9 View Fig ). Cuticle black, except more or less orange translucent areas on tergites 2+3 covered by dense silvery reflecting microtrichia (‘silver spots’); broad (tergite 2 is 1.9–2.4, tergite 3 is 2.2–3.5 × as wide as long); silver spots on tergites 2+3 large, almost reaching the corners, tapering towards middle of tergite; distance between silver spots on tergite 2 relatively large, 0.2–0.25 × width of tergite; in tergite 3 small, 0.11 × width of tergite; tergite 4 usually with small white non-reflecting microtrichiose spots in median part; tergites light yellow setose, except large area of silver spots without setae, and short black setae on tergite 2 posteriorly, black cuticle of tergite 3, anteromedially and below microtrichiose spots on tergite 4 mixed with yellow setae. Sternites brown, densly microtrichiose, covered with long light yellow hairs of more or less even length.

MALE GENITALIA ( Figs 10A View Fig , 11A View Fig , 12A View Fig , 13 View Fig A–C). Cerci relatively large, shaped as one quarter of a circle. Median surstyle covered with relatively narrow, longitudinal stripe of microtrichia interiorly; deeply hollowed posteriorly towards posterior surstyle; with inner, acute accessory lobe; ventral margin more or less straight. Posterior surstyle with hooked process recurved in the direction of median surstyle and at the base with external, long setose, bump. Base of epandrium as high as long. Hypandrium sickleshaped, with rather wide distal part, tapering towards apex; base wide, without deep groove.

PUPARIUM ( Fig. 14 View Fig ; n=6). Integument rough, dull brown. Dorsally, two pupal spiracles ( Fig. 14A View Fig :x) project from the middle of the operculum, widely separated by a distance of 4 × their length. These processes are conical structures, = 0,04 mm long, pointed apically and with numerous disc-shaped tubercles, distributed irregularly on almost the entire surface ( Fig. 14B View Fig :y), except the apex ( Fig. 14C View Fig ). Each tubercle has 4–8 spiracular openings radially arranged ( Fig. 14D View Fig ). Surface between tubercles and on apex of process rough, reticulate, divided in hexagonal areas. Posterior respiratory process ( Fig. 14 View Fig E– F) with total length = 0.23 mm, length between transverse ridge and centre of spiracular plate (a): = 0.30 mm, width at level of the ridge (b) = 0.45 mm, a/b= 0.67; short and broad (like in Merodon ), wider than long, strongly ridged in proximal half (spiracular plate ( Fig. 14E View Fig ) not studied due to poor condition of specimens, but seems to have four pairs of spiracular openings like in Merodon , not three pairs like in Eumerus ). Cephaloskeleton as in Fig. 4G View Fig .