Heteralonia (Isotamia) Bezzi

Greathead, David J., 2006, New records of Namibian Bombyliidae (Diptera), with notes on some genera and descriptions of new species, Zootaxa 1149 (1), pp. 1-88 : 16-17

Heteralonia (Isotamia) Bezzi

Isotamia Bezzi, 1912: 606 (as genus). Type species: Isotamia daveyi Bezzi, 1912 .

Heteralonia (Isotamia) ceuthodonta (Hesse)

Heteralonia (Isotamia) ceuthodonta ( Hesse, 1936: 180) .

This species was described from a single female collected in Botswana and no further specimens have been reported until the present. Both sexes are represented in the material from NMNW and enabled the identification of specimens from East Africa in the authors collection (DJGC). The male can now be described and an indication given of geographical variation.

It is similar in habitus to other African Isotamia spp. but the hyaline posterior part of the wing has more spots on cross­veins, like H. (I.) loxospila Hesse and Indian species belonging to the H. (Isotamia) siva (Nurse) species group. However, unlike these Indian species and all African species so far known, the scales on the body are ochreous and not dark brown or black and white.

Description. East African specimens. Male. Size: length, 7 mm; proboscis, 2 mm; wing, 6 mm. Body: black, except for light brown margins of oral cavity and underside of head. Head: ocellar triangle placed in front of vertex on frons by a distance equal to its length, face conical. Sparse black hairs on frons and face, denser on oral rim and with narrow gold scales beneath; occiput with a fringe of minute glistening hairs on margin of central cavity and with gold scales, denser at margins of eyes. Eye indentation shallow, bisecting line as long as scape and pedicel. Antenna with scape 1½ length of pedicel and with a few black hairs, first flagellomere twice length of scape, tapered from underside to form a truncated elongate cone, second flagellomere as long as pedicel, robust lanceolate and with a minute style. Proboscis longer than head, projecting beyond oral cavity, palpi narrow, as long as antennae and with a few hairs. Thorax: black bristles, ochreous yellow hair on fore margin of mesothorax (collar) and along notopleural line, mesonotum and scutellum with fine black hairs and elongate gold scales, propleuron and anepisternum with mixed black and ochreous yellow hairs, metatergal tuft black above and ochreous yellow below, katepisternum with a patch of elongate gold scales, remainder of pleuron bare. Legs: Black with black bristles and gold scales, fore legs not reduced but fore tibiae spiculate, mid femora with two and hind with four ventral bristles. Claws almost straight. Wing: (Fig., 8) narrowed at base, costal hook small black, costal comb not developed, alula small rounded. Veins brown, membrane infuscated brownish at base, in costal and subcostal cells, cell br, R 1 to level of end of subcostal, bases of bm, anal and axillary cells; also with small dark brown spots at origin of R 1, origin of Rs, r­m cross­vein, fork of R 2 and R 3, interradial cross­vein, base of dm, m­m cross­vein, apex of bm. Cell dm narrow, m­m short, almost straight and oblique to wing margin so that the cell appears truncate, rm cross­vein distinctly before middle. Cell r5 markedly narrowed towards wing margin. Squama white and with a white fringe. Haltere brown with apex of knob paler, whitish. Abdomen: first tergum with ochreous hair at sides and a fringe of yellow scales, second tergum with pale ochreous yellow hair at sides, remainder with sparse black hairs and scales at sides; dorsal surface covered in loosely attached glistening silvery gold scales and the hind margins of the terga fringed with dense yellow scales; sterna with fine yellow hairs and sparse gold scales. Genitalia (Fig., 6) very small, typical for the genus with weakly developed apodemes concealed within fused gonocoxae and simple tongue­shaped epiphallus.

Female. Size range 6–9 mm. Similar to males but a variable number of hairs on head brownish golden and not black; only bristles and fine hairs on dorsal surface of mesonotum and scutellum black, remainder ochreous yellow; tibiae and tarsi brown in some specimens; scales on abdomen uniform dull ochreous yellow not glistening, few if any black scales at sides. Wing may have a short appendix on the bend of m­cu projecting into cell dm and cell r5 closed on wing margin.

Males, like females, are variable in the number of black hairs, especially on pleura where there may be few black ones and in the wing characters.

Specimens from Namibia differ from those described from east Africa as follows: scape tending to be brownish not black. Scales all dull ochreous yellow, hair on thorax all ochreous yellow, only bristles black. Legs brown in middle darker blackish on basal halves of femora and tarsi. Wing infuscation (Fig., 9) darker brown and sharply marked off from the hyaline area and with paler brown areas in basal half of r1 and in bm; spots blackishbrown. Sometimes with an additional spot on R 2 between its separation from R 3 and the bend on one or both wings. Cross­vein m­m even shorter and more oblique to margin so that dm more rectangular at apex. Abdomen without black hair or scales at sides, scales ochreous yellow not glistening in males but similarly dull ochreous yellow in both sexes.

These specimens were collected in Malaise traps and have been dried and pinned after storage in alcohol. This treatment may account for the tendency to paler colour of the cuticle and the absence of glistening scales on the abdomen of the males. However, the darker wing markings are most unlikely to be a result of storage in alcohol and this character and the reduced number of black hairs and bristles indicate geographical variation in what is considered to be a single species.

Distribution. Botswana, Kenya, Namibia , Tanzania.

Material examined. KENYA: 1♂, 1♀, near Kajiado, 14.v.1968, D.J. Greathead ; 2♂♂, 2♀♀, Kajiado, 27.iv.1967, D.J. Greathead ; 1♂, Masai Bissel , 27.iv.1967, D.J. Greathead, (all DJGC) . TANZANIA: 2♂♂, near Kondoa , 20.iv.1967, D.J. Greathead ; 1♂, 70 miles N of Dodoma, 2.v.1966, D. & A. Greathead ; 1♂, 1♀, 50–70 miles N of Dodoma , 20.iv.1967, D.J. Greathead ; 2♀♀, 15 miles S of Longido , 30.iv.1966, D. & A. Greathead, (all DJGC) . NAMIBIA : 3♂♂, 1♀, Waterburg Pl. Park, Restcamp , 20°30’S 17°14’E, 6–13.iv.1993, S.V. Green, Malaise trap ; 3♀♀, Okahanja District, Erichsvelde 44, 21°35’46”S 16°56’16”E, 20–22.iii.2003, A.H. Kirk­Spriggs, Malaise trap sample, (all NMNW) .