Usia aenea (Rossi, 1794)

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 : 64-66

Usia aenea (Rossi, 1794)

( Figure 3 , Figure 4 , Figure 16 , Plate XVII)

Bombylius aeneus Rossi, 1794: 78 .

Usia vicina Macquart, 1840: 105 [1841: 383], syn. nov.

Type material of U. aenea . Not seen and apparently missing. Rossi was a contemporary of Meigen who exchanged specimens with others so it has been postulated that the three Meigen specimens in MNHN might be syntypes. However, this is very unlikely as all specimens seen from mainland Italy, the type locality, are the shorthaired form, whereas the three Meigen specimens are all long-haired forms so probably from Spain or France.

Type material of U. vicina examined. LECTOTYPE here designated; France, Museum Paris, France Merid., Dufour 135-38/ 11,38 [round white label]/ 5/ TYPE [red][♀ long-haired form; very mouldy so difficult to interpret but only missing left fore-leg and right hind-leg, in Macquart coll. MNHN].

Originally described from an unspecified number of specimens. A single female syntype was found in the Macquart collection in MNHN which becomes the lectotype.

Other material examined. Short-haired form France, Var, Toulon, Le Lavandou, Foret de Dome, N43º11′ E6º22′, 3 June 2002, leg. D.A. & E.T. Levy [♂] ; July, Museum Paris, St Aygulf, Var, R. Azle 1929 [♀] ( MNHN) . Italy, Lazio, Piano de Rascino, 19 vi 2003, leg. D.J. Gibbs [♂♀] ( PCDG).

Long-haired form France, Museum Paris, France, Royan, (Carente-inf.), Ch. Delval, 1902, Roytan, July 0 2 [♀] ; Arcachon, Gironde, June–July 1912, Coll. A. Bayard, Usia aenea Rossi , Museum Paris, ex coll. Hesse [♂] ( MNHN) ; Portugal, Minho, Vilar da Veiga, 20 June 2005, leg. C.E. Dyte [♂] ( PCDG) ; Algarve, Parque Natural de Ria Formosa, 4 May 1998, leg. P.M. Pavett, NMWZ 1998 0 53 [♂] ( NMWC) . Spain, Trujillo, N39º50′ W5º30′, 500m, 4 May 2001, E leg. B. Merz [♂] ( MHNG) ; Bnco., Moreno, S.Almijara-Má leg. A. Cobos; ex coll. B. Aldgren ♂.

Mixed characters. Italy, Sicily, Etna 3km NW of Milo 1000m 9 June 1999 leg. B. Merz [♀] ( MHNG) .

Etymology. aeneus from Latin meaning “bronzy”; vicina from Latin meaning “similar” or “kindred” presumably referring to its similarity to other Usia .

Diagnosis. Often a fairly large species but diminutive specimens are not uncommon, one of the commonest Usia , especially in Italy and Iberia. An all black species, in natural light often with a bluish hue, erect whitish vestiture of variable length. Occiput densely grey dusted, oral margin very narrow, frons shining black. Mesonotal cuticle distinctly punctured but not so roughened to eliminate all smooth shining areas. Wings in most specimens with clear pattern of yellow base, brown mid-anterior patch and clear tip and trailing edge. Genitalia fairly small and globular, lacking lateral horn-like projections on the gonocoxa.

Redescription. Measurements. Body length. 3.0– 8.7mm. Wing length. 2.7–6.5mm.

Male. Head. Oral margin narrow, almost linear, disappearing below, shining black to brownish. Frons black, shining, conspicuously grey-dusted anterolaterally often with some fine striations but not enough to eliminate the shine. Eyes separated at their narrowest by about one fifth to one sixth head width, a little more than width across lateral ocelli inclusive. Lateral ocellus separated from the eye margin by one to two times the diameter of that ocellus. Ocellar tubercle shining, undusted, eye margins in front of anterior ocellus diverging relatively evenly to rear of oral opening. Translucent white hairs on ocellar tubercle varying from as long as width across lateral ocellus (short-haired form) to rather more than the width of the frons (long haired form). Rear of frons in front of anterior ocellus with short, strongly proclinate uniserial lines setulae close to eye margins (long haired form) or glabrous here (short-haired form), anterior part of frons with a scattering of short setulae across most of width in places. Occiput densely grey dusted, the black ground colour obscured except on a triangular area behind ocellar tubercle which is shining black, this often extended to neck. A fairly dense covering of white hairs across dusted area, shorter and more even above, significantly longer close to lower oral margin. Ommatidia uniform in size across the eyes. Antennae black, third segment, about longer than twice length of scape and pedicel together (long-haired form), significantly shorter in the short-haired form. narrow swollen below basally, concave medio-ventrally, sensilla inconspicuous, translucent brownish. All antennal segments with very short brown hairs above, longest just before apical sulcus. Palps small, black, apically, clavate tip a little wider than oral margin, the pale apical setae about half as long as the length of the palps. Proboscis shorter than head-thorax length, black, dorsally hairless. Thorax. Mesonotum shining black with faint bluish hue under natural light, grey dusting on anterior slope of mesonotum laterally, post-pronotal lobe, notopleuron and above wing root. Disc densely punctate, on disc some areas of smooth cuticle greater than the diameter of a puncture. Paramedian vittae usually readily discernable by their different surface sculpture, faintly transversely wrinkled and impunctate, extending from anterior slope of thorax almost to wing insertions. Mesonotum fairly densely clothed with fine whitish vestiture, in the long-haired form with mid-length hairs anteriorly and laterally, towards scutellum both long and short hairs present; in the short-haired form shorter and neater hairs anteriorly and laterally contrasting with very short, proclinate hairs close to scutellum. Acrostichal hairs between the bare paramedian vittae multiserial, entirely reclinate, widening posteriorly, dorsocentrals not distinguishable from the general vestiture. Scutellar punctuation and hairing as adjacent parts of mesonotum, marginal hairs more than half mid-scutellar length (long-haired form) or very short, less than a fifth mid-scutellar length (short-haired form). Pleurae uniformly grey dusted largely obscuring ground colour, except for a narrow strip of shining cuticle along the anterior margin of the anepisternum (long-haired form) or anepisternum dusted on a vertical central strip only and a shining patch in middle of anepimeron (short-haired form). Long white hairs, a little longer than any on mesonotum, on pronotum and across whole of the anepisternum. Wing. Membrane with distinct brown markings extending from costa to vein M contrasting with yellow base proximal to the humeral crossvein. This infuscation different in the two forms, isolated spots of infuscation over origin of R4, r-m and m-cu, 1st basal cell clear subapically, 2nd basal cell largely clear (long-haired form)( Figure 3 ), infuscation of wing filling 1st and 2nd basal cell so no isolated darker spots over origin of R4, r-m and m-cu are discernable (short-haired form)( Figure 4 ). Veins all dark brown except proximal to humeral crossvein where they are paler, yellowish. Crossvein r-m close to the middle of discal cell, conspicuously beyond dm-cu. Anal lobe moderately well developed, with evenly curved trailing edge, a little narrower than width of anal cell but variable, in some individuals of long-haired form it is narrow, only about half width of anal cell. Haltere. Yellow, base of stem slightly brownish. Legs. Coxae black with a coating of grey dust like that on the pleurae. Remainder of legs black, undusted, shining below the setulae. Coxae externally and femora ventrally covered with moderately long, white hairs, on the mid and hind-femora a little more than the greatest depth of the femora, shorter on front femora (long-haired form), or not much longer than depth of tibia (short-haired form). Femora dorsally and tibia rather densely covered with short, recumbent, yellow-brown setulae some longer more erect hairs on tibia basodorsally (lacking in short-haired form). Abdomen. All tergites shining black, often with faint bluish reflections, slight dusting on down-curved margins, only obvious on first tergites. Each tergite densely puncto-rugose, surface sculpture of transverse welts each furnished with a hair, very narrow, often shining, sometimes reflexed apical margin. Disc uniformly and densely covered with short to very short, pale brownish, recumbent hairs, longer and more erect laterally. Sternites grey dusted, faintly punctate, with fairly long, erect white to very pale yellow hairs. Genitalia. Relatively small and simple, globular. Epandrium flask-shaped with apicolateral blunt extensions, longer in short-haired form, mostly shining black, the cuticle punctate evenly coated with pale yellow curved hairs. Gonocoxite about twice as broad as long, shining black, the two forms differing in small details, hairs rather longer than on epandrium, gonostyli ‘S’-shaped.

Female. As male except as follows: oral margin slightly broader. Frons marginally wider, about one-fifth head width, lateral ocelli separated from eye margin by about twice their diameter. Short setulae on front of frons between grey dust spots fewer. Anal lobe of wing averages wider, the trailing edge more convex, than males from the same population. Genitalia. Tip of abdomen coming to a rounded point; apical sternite rather rectangular, a little longer than deep, apical notch very small, barely visible in undissected specimens. Apical sternite strongly domed basally, apicomedial area covered in grey dusting. Furca pigmented, coming to a blunt point, arms short, lacks any pigmented vaginal plate.

Discussion. Usia vicina Macquart was synonymised under U. atrata Fabricius by Becker (1906b) (which he misinterpreted, applying this name to U. pubera Strobl and using U. claripennis Macquart for the true U. atrata ). Despite the mouldy condition of the Macquart lectotype, it is quite clearly an example of U. aenea Rossi and quite unlike U. pubera (= U. atrata of Becker). As Becker (1906b) claims to have examined the Macquart types, his conclusion is surprising. Even if the Rossi types were unavailable even then, as seems likely, Becker certainly seems to have interpreted U. aenea correctly otherwise.

The possibility of the two forms of this species being sufficiently distinct to be named as different species needs to be considered. When examining extreme examples the more discrete wing pattern, narrow anal lobe and dusted anepisternum of the long-haired form provide better characters than are used to justify other Usia species. The male genitalia also show differences, the shorter epandrium and different tip to aedeagus in long-haired forms, that might support separation. However, on examining a large number of specimens it became apparent that the width of the anal lobe was highly variable, although always narrower in long-haired form, and the male genitalia seem to be rather unstable. A further complication comes with a female specimen from Sicily which has long vestiture but a wing pattern and anepisternum dusting of the short-haired form. Given this ambiguity it seems best to retain them as a single, rather variable, species for the moment.

Distribution. A relatively frequently found species in southern France, Italy (including Sicily), Portugal, and Spain. The long-haired form is known from Iberia and along the Atlantic coast of France north at least to Saintes. The short-haired form occurs in Italy and along the French Riviera almost to Toulon. A single specimen examined from Sicily exhibited mixed characters.

Figures

FIGURE 3. ♂ U. aenea wing of long-haired form.

FIGURE 4. ♂ U. aenea wing of short-haired form.

FIGURE 16. ♀ U. similis (left) & U. aenea (right) frons dorsally.