Merodon nasicus Bezzi 1915

Merodon nasicus Bezzi, 1915

Figs 1, 4F, 5F, 6F, 9F, 10F, 11F, 12F, 14E, 15E, 16E, 18D, 19D–F, 20, 23A–B

Merodon nasicus Bezzi, 1915: 102 (type locality: Kenya, Njoro).

Small (6–7 mm), black species with narrow, white pollinose, tergal fasciae. Oral margin distinctly protruded (Fig. 9F); face and frons without pollinosity, except narrow vitta along eye margins; terga 2–4 with medial pollinose fasciae (Figs 5F, 14E); tergum 4 covered with whitish to yellowish pile; male genitalia with S-shaped posterior lobe of surstyle, gradually narrowing toward tip (Fig. 19D: pl), anterior margin of surstyle rounded in lateral view (Fig. 19D: ams). Differs from Merodon bombiformis, M. vittatus sp. nov., M. multifasciatus and M. zebra Vujić & Radenković sp. nov. by absence of distinct pollinose vittae on scutum (conspicuous in these four species); narrow medial pollinose fasciae on terga 3 and 4 (broad in M. vittatus sp. nov., M. multifasciatus and M. zebra sp. nov.) and male genitalia with moderately broad posterior lobe of surstylus, narrower than in M. multifasciatus, but broader than in M. vittatus sp. nov. and M. zebra sp. nov. (Figs 7A, D: pl, 19D: pl). Similar to M. lotus sp. nov. from which differs in presence of distinct medial pollinose fasciae on terga 2 and 3 (absent in males and indistinct in female of M. lotus sp. nov.) and more protruded oral margin (Fig. 9E–F).

Lectotype (designated here by A. Vujić) KENYA • 1 ♀; Njoro, about 140 km NW of Nairobi; 0.37° S, 35.917° E; 2322 m a.s.l.; date unknown; A.J. Cholmley leg.; BMNH NHMUK010369943.

Bezzi published the Syrphidae of the Ethiopian Region with the descriptions of two new species, Merodon planifacies and M. melanocerus (Bezzi 1915). In the same work, he presented diagnostic characters for, and notes on, the third Ethiopian species, M. nasicus, referring to 1914 as the year of its description (Bezzi 1915: 102), based on material from Eritrea in the collections of the Hungarian Museum. Bezzi (1915) also stated that there was a single female specimen of this species from Njoro, in British East Africa. Subsequently, in the Catalogue of the Diptera of the Afrotropical Region (Smith & Vockeroth 1980), and in the Diptera Database (Evenhuis & Pape 2020), this Njoro specimen was erroneously considered as the holotype. Shortly after his 1915 monograph, Bezzi published a description of Lampetia (Merodon) nasica (Bezzi 1921), based on a male and female from Eritrea in the collection of the Hungarian Museum. This is actually the unpublished description from 1914 (Bezzi 1915). However, based on International Code of Zoological Nomenclature (International Commission on Zoological Nomenclature 1999), the oldest available name for a taxon is its valid name, therefore the publication with the first appearance of the name of the taxon (Bezzi 1915) should be considered as valid. Following from this conclusion, in addition to specimens from Eritrea, cited in both publications (Bezzi 1915, 1921), one female specimen from Kenya (Bezzi 1915), deposited in BMNH, also belongs to the syntype series. The Diptera collection in the Hungarian National Museum in Budapest, including the syntypes from Eritrea, was destroyed by a fire in 1956. However, in order to stabilize nomenclature should additional specimens of the type series be found, we designate the specimen from BMNH as lectotype.

Additional material

BURUNDI • 1 ♂; Bururi; 3.951° S, 29.619° E; 1950 m a.s.l.; 20 Mar. 1949; F.J. François leg.; FSUNS ID 21976; RBINS.

ETHIOPIA • 1 ♂; Welo Gondi, 60 km SW Lalibela; 7.779° N, 35.458° E; 2485 m a.s.l.; 9 Oct. 2005; A. Freidberg leg.; FSUNS ID 04972; TAUI.

ERITREA • 1 ♀; Adi Keyh (on eastern slope of Ethiopian highlands); 14.816° N, 39.383° E; 2442 m a.s.l.; Sep. 1902; Dr A. Andreini leg.; LSF.

Original description without any illustrations was based on single male and female (Bezzi 1921).

Length: small sized species, body 6–7 mm, wing 5–6 mm (n =2).

Male

HEAD (Figs 4F, 9F, 11F, 12F). Antenna (Fig. 4F) reddish-brown; pedicel elongated, approximately as long as basoflagellomere (relation scape: pedicel: basoflagellomere =1.0: 3.0: 3.0); basoflagellomere concave dorsally, with acute apex; arista reddish-brown, thickened basally, 1.3 times as long as basoflagellomere. Face black, without pollinosity, except along eye margins and covered with whitish to yellowish pile, except on bare medial vitta that occupies ½ width of face. Oral margin strongly protruded (Fig. 9F). Frons black, without gray pollinosity, except eye margins, covered with whitish to yellowish pile. Vertical triangle isosceles (Fig. 12F), usually dark brown, predominantly covered with a long, yellow pile. Ocellar triangle equilateral. Eye pile black in upper half and gray in lower, as long as scape. Eye contiguity about 15–18 ommatidia long. Occiput black, partly pollinose, covered with yellowish to whitish pile.

THORAX (Fig. 6F). Mesonotum dark brown, covered with light yellowish to yellowish pile; scutum without or with indistinct pollinose longitudinal vittae; postpronotum and anterior margin of scutum with sparse gray pollinosity. Pleuron dark brown, covered with gray pollinosity and the following parts with whitish to yellow pile: anterior part of proepimeron, posterior part of anterior anepisternum, most of the posterior anepisternum except anterior end, antero-ventral and postero-dorsal part of katepisternum, anepimeron, metasternum. Wing hyaline, mostly covered with microtrichia; veins yellow to brown. Calypter pale yellow. Halter with yellow pedicel and capitulum. All three femora dark brown to black, except reddish apex; tibiae mostly reddish, medially dark brown; basal three tarsomeres yellowish to reddish, the rest blackish (Fig. 6F). Metatrochanter without calcar. Metafemur moderately thickened, with less developed apicoventral triangular lamina, more or less dentate, the apical dens is distinct (Fig. 6F). Pile on legs predominantly whitish to yellow.

ABDOMEN (Fig. 5F). Dark brown with yellow to whitish-yellow pile on lateral margins. Tergum 1 usually with pollinosity at least laterally, covered with short pile; tergum 2 with narrow medial fascia interrupted in the middle, covered with whitish pile; tergum 2 medially mostly covered with short black pilosity; terga 3 and 4 with or without narrow pollinose posterior margin and distinct medial fascia interrupted in the middle; tergum 3 covered with short black pile medially; tergum 4 covered with longer whitish to yellowish pilosity, except few black pile in anterior half. Brown sterna pollinose, covered with white or yellow pile.

GENITALIA (Figs 18D, 19D–F). Posterior lobe of surstyle moderately broad, bent, S-shaped, gradually narrowing toward tip (Fig. 19D: pl); anterior lobe of surstyle undeveloped (Fig. 19D); anterior margin of surstyle rounded in lateral view (Fig. 19D: ams); cercus square like (Fig. 19D: c). Hypandrium with theca medially distinctly narrowed (Fig. 19F). Lateral sclerite of aedeagus small, pointed (Fig. 18D: s).

Female (Figs 14E, 15E, 16E, 20)

Similar to the male except for normal sexual dimorphism: metafemur usually with very small apical dens on triangular lamina (Figs 16E, 20B); frons with non pollinose medial vitta (Fig. 15E); vertex shiny, non pollinose, mostly covered with black pile.

Period of flight and distribution (Fig. 1)

Merodon nasicus is known from Kenya, Ethiopia, Eritrea and Burundi. On the basis of our data, the flight period was found to be in March and from September to October. This species occurs only on high mountains at elevation between 2000 and 2500 m a.s.l. in vegetation of montane forest-tundra (Sayre et al. 2013).