Usia angustifrons Becker, 1906a

Gibbs, David, 2014, A world revision of the bee fly tribe Usiini (Diptera, Bombyliidae) Part 2: Usia sensu stricto, Zootaxa 3799 (1), pp. 1-85 : 77-80

Usia angustifrons Becker, 1906a

( Figure 9 , Plate XXII)

Usia angustifrons Becker, 1906a: 14 [ 1906b: 212].

Type material of U. angustifrons examined. LECTOTYPE here designated; Tunisia, V [May], 52720/ angustifrons Beck / Typus / Zool. Mus. Berlin [♂] ( ZMHB) . PARALECTOTYPES; Tunisia, V [May], 52720/ angustifrons Beck / Typus / Zool. Mus. Berlin [1♂ 1♀] ( ZMHB).

Originally described from an unspecified number of specimens of both sexes. Three syntypes were found in ZMHB, the male in best condition was selected as lectotype.

Other material examined. Tunisia, 10km E. of Kairoun, 5 May 1975, leg. J.W. Ismay 2♂ 3♀ ( OUMNH).

Etymology. From Latin angustus meaning “narrow” + frons meaning “forehead”, “brow” or “front”.

Diagnosis. Small shining black species known only from Tunisia. Entirely black, sometimes with faint gold and green reflections, especially in females, vestiture fine, white, acrostichals erect or reclinate. Occiput shining along narrow strip just behind upper eye margin, otherwise thinly dusted. Male eyes separated by diameter of anterior ocellus, more closely approximate than any other Usia species, front half of frons entirely grey dusted obscuring ground colour. Female frons parallel in posterior half, abruptly diverging in anterior half, grey dust spots broad, central undusted strip narrower than an individual dust spot. Longest scutellar vestiture about half scutellar mid-length but variable, longest hairs can be few or missing through damage. Pleurae entirely grey dusted. Wings clear, anal lobe very narrow, a little more convex than in female but still narrower than anal cell in female.

Redescription. Measurements. Body length. 6.5–9.0mm. Wing length. 6–7mm.

Male. Head. Mouth-margin very narrow, almost absent, dark brown or black. Frons at narrowest point narrower than any other Usia species, no wider than the diameter of the anterior ocellus, lateral ocellus almost touching the eye margin. Ocellar tubercle shining black, frons at narrowest point dull but still black, anterior part of frons entirely pale grey dusted obscuring dark ground colour. Occiput black, shining, undusted on a narrow band behind upper eye margin, otherwise with a thin covering of pale dust that does not obscure ground colour, triangular area behind vertex more thinly dusted. Ommatidia all of uniform size. Hairing moderate length, on ocellar area about as long or a little longer than width of vertex level with lateral ocelli, frons glabrous. Antennae black, third segment longer than the scape and pedicel together, all segments with very short setae above, sensilla small, brown or pale. Proboscis black, hairless, about as long as the head and thorax together; palps very short and thin, black to brown with short pale hairs apically;. Thorax. Mesonotum and scutellum shining black except anterior slope of between paramedian lines post pronotal lobes, dorsum of post pronotal lobes, most of notopleuron and above wings which is grey dusted. Disc shining except for relatively simple punctures, many separated by areas of smooth cuticle greater than diameter of a puncture. Bare paramedian lines relatively conspicuous, extending back to beyond the mid point of the mesonotum, each about as broad as the midline which has 5–6 lines of hairs. Pleurae with a covering of grey dust sufficiently dense to obscure the black ground colour. Mesonotum and scutellum covered with mid-length pale yellowish white hair, that on the disc of the mesonotum about as long as the width of the vertex at the lateral ocelli. Pronotum and posterior edge of anepisternum with a scattering of white hairs. Wing. Wing membrane clear, becoming yellow basally and in costal cell, the veins also yellow basally becoming conspicuously darker brownish black in the apical half. Base of stem of R darker brown, base of C blackish. Anal lobe narrow, almost linear, conspicuously narrower than anal cell, r-m a little beyond the middle of the discal cell. Haltere. Yellow, becoming brown at base of stem. Legs. Entirely black, the coxae grey dusted as in pleurae; femora with rather short, pale hairs, the longest not exceeding the greatest depth of the tibia, tibia and tarsi with only a covering of short setulae, pale on tibia, browner on tarsi. Abdomen. Shining aeneous black, the disc of the tergites covered with short, whitish hairs, the hairs arising from transverse welts forming a rugose surface sculpture. Laterally and on the down-curved margins the tergites are clothed with rather longer, whitish hairs. Sternites grey dusted with whitish hairs confined to the posterior margin. Genitalia. Fairly small and partially enclosed in apical tergites, few useful details visible in pinned specimens, shining black, tip of gonocoxite often browner, covered in yellowish hairs, longest on the gonocoxite.

Female. As male except as follows: broader, thought still linear, oral margin and the conspicuously wider frons, the lateral ocellus separated from the eye margin by about the diameter of that ocellus. Posterior half of frons shining black, parallel sided, about four times the diameter of the anterior ocellus and as wide or wider than the length of the longest hairs on the ocellar tubercle, a few tiny, proclinate hairs close to eyes forward of anterior ocellus. Anterior half of frons widening rather abruptly, more than lateral third each side covered in dense whitish dust obscuring ground colour, central shining black strip narrower than dusted areas. Third antennal segment sometimes shorter. Anal lobe broader, margin more convex, almost as broad as the anal cell. Abdomen conical tapering to a rounded point, apical sternite evenly convex, wider than long, apical emargination small and shallow, in dry specimen a square spot of pale dust discernable apicomedially.

Discussion. The affinities of this small African species are not at all obvious. It has a pattern of dusting on the occiput similar to some of the U. florea group but is otherwise quite dissimilar. The narrow anal lobe and form of the gonostyli are reminiscent of some of the U. bicolor group but the epiphallus and female genitalia do not conform to that group. It does not seem to be closely related to any known species.

Distribution. Only known from Tunisia. Specimens are few, so it appears to be rare and local.

Figures

FIGURE 9. ♂ U. angustifrons head and mesonotum dorsal.