Namibimydas prinsi, Hesse, 1974

Hesse, A. J., 1974, A new South African representative of the South West African genus Namibimydas Hesse (Diptera: Mydaidae), with some ecological notes on the habits of the species, Annals of the South African Museum 66 (2), pp. 25-34 : 26-31

Namibimydas prinsi sp. nov.

This new species which I have great pleasure in dedicating to Mr A. J. Prins, who first discovered it, is characterized as follows:

Body-colour with the head and body mainly dark or blackish, appearing darker or more black in ♂♂, sometimes more greyish black in ♀♀; pleural and sternal parts and venter in some ♀♀ (tenerals) appearing pallid; sides of mesonotum, postalar calli, scutellum and metanotum in some ♀♀ (probably teneral) also sometimes paler, more obscurely pallid to dirty yellowish; lower part of buccal cavity (more extensive in ♀♀), anterior spiracles and notopleural suture, sclerites below wing-bases, posterior thoracic spiracles or part below halteres, hind margins of tergites 3-7 in ♂♂ and 2-7 in ♀♀, especially on sides, the sides of tergites obscurely in teneral ♀♀, lateral and posterior margins of hypopygial tergite 9 of 33, processes and broad sides of navicular sternite 9 in ♂♂, and the acanthophorites and spines in ♀♀ yellow or yellowish; bullae, even in ♂♂, rather small, dull blackish red to black, elongate-oval, far apart along hind margins of tergite 2, very much smaller in ♀♀; antennae mainly dark blackish brown to black, only the articulations between the joints and the terminal tubercles usually paler, more pallid or yellowish (the entire antennae in teneral ♀♀ appearing subpallid or dirty yellowish); proboscis blackish brown to black, paler in tenerals; legs in ♂♂ with the coxae blackish brown to black, the middle and hind ones, especially latter, more yellowish brown towards apex below, the front femora mainly blackish brown, only the lower apical half yellowish, the middle and hind femora blackish brown above, yellowish below, the bases of hind ones also tending to be more yellow, with all the tibiae narrowly darkened above to a variable extent, the hind ones more evidently so apically, the tarsi mainly yellowish, but also slightly darkened above on apical parts of the joints, the last 2 or 3 joints sometimes more extensively darkened, the claws black in apical halves; legs in ♀♀ more extensively pallid or yellowish, more indistinctly or scarcely darkened on femora and tibiae above, the legs entirely pallid or yellowish in teneral forms.

Inregumenr of head and body mainly dull, covered with greyish white tomentum to a variable extent; part of median ocellar ridge, antennal joint 3, head below on each side of buccal cavity, and the proboscis more or less shining; thorax above mainly dull, leathery, with setiferous puncturation; pleurae also mainly dull, the middle part of sternopleuron, not covered with tomentum, shining to a variable extent; metanotum dull, leathery; abdomen dull above, setiferously punctured, the minute punctures lodging the hairs, the extreme sides of tergites tending to be more shiny, especially in ♀♀; the sides of tergites 2-7 in 22, especially intramarginally, rugose, transversely striate in ♂♂, tergite 7 in ♀♀ transversely coarsely striated or grooved discally, and to a certain extent also on tergite 6 laterally and posteriorly; hood-like tergite 8 in ♀♀ punctured, less coarsely transversely striate, also more shining; sternum shining; venter in both sexes shining or subshining, transversely striated in ♀♀, less distinctly so in ♂♂; hypopygium in 55 mainly dull, but basal junction between tergite and sternite 9, to a certain extent sides of 9, and keel of 9 Shining; acanthophorites and their spines in ♀♀ also Shining; legs, including coxae, more or less shining, the femora finely transversely striate, and the coxa, also more or less striate laterally.

Vestíture on head, body and legs mainly snow white in both sexes, longer and denser in ♂♂ than in ♀♀; that on head long, dense and conspicuous in ♂♂, slightly shorter in 22; postvertical bristles white, slender, hair-like, diificult to see among the dense occipital hairs, more discernible in ♀♀; hairs on occipital part laterally behind eyes shorter than rest of cephalic hairs, shorter in ♀♀; palps with a tuft of long hairs and base of proboscis below also with some long hairs; head in front and sides of occiput dull, covered with fine greyish tomentum, denser and more evident along eye-margins; hairs on thorax above in front longer and denser than on rest of thorax, shorter in ♀♀; those on disc of mesonotum shorter and sparser, shorter in ♀♀, leaving a bare streak on each side in posterior half in both sexes, with a tuft of longish hairs medially in front of scutellum, and also with longish ones along notopleural part, above wing-bases, and on postalar calli; metanotum mainly bare on greater middle part, but with long hairs on sides; pleurae thinly covered with greyish tomentum, dull, except for the more shiny sutural and sternopleural parts, with an upper posterior tuft of long hairs on mesopleuron, long hairs along its posterior margin, long ones on pteropleuron and dense ones on metapleuron anterior to halteres and posterior thoracic spiracles, the hypopleuron mostly bare except, for some long hairs along its posterior coxal border; abdomen in ♂♂ with fairly dense and long snow white hairs, those on tergites 1 and 2, especially on sides, slightly longer and denser, but those on sides of 3-5 in tufts, scarcely shorter, and those on sides of rest of tergites also long, but less in tufts, those on hypopygium, where present, also long and conspicuous, the hairs on venter in ♂♂ slightly sparser than on abdomen above, but also long, with the hairs on abdomen above in ♂♂, when viewed from above, more or less concentrated medially on tergites 3-7 in form of rosette-like tufts; hairs on abdomen above in ♀♀ long and dense only on tergite l, especially on sides, with only a small tuft of shortish ones on sides of tergites 2 and 3, the rest of surface above on tergites 2-6 with minute, decumbent hairs in fine setiferous punctures and which in certain lights have a sericeous yellowish tint, with the hairs on tergite 7 and the posterior genital tergite 8 longer than the minute ones on preceding tergites, more sericeous white and directed forwards, with the abdomen above in ♀♀ also densely covered with greyish white or slaty grey tomentum on tergites 3-7 (this is sometimes denuded to a variable extent), the hairs on acanthophorites and anal lobes yellowish to golden yellowish, with the hairs on venter in ♀♀ minute, much sparser than on tergites, tinted slightly sericeous yellowish in certain lights, those on sternite 7 also sparser, but longer than on preceding sternites and directed forwards as on tergite 7; hairs on legs in ♂♂, especially on femora, denser, longer and more bushy than in ♀♀ in which sex the longer ones are distinctly less dense, especially on hind legs.

Head much broader than across broadest part of thorax, quite 3,8—4 mm in 33 and 3,68—4,04 mm in ♀♀, though on the whole the head of ♀♀ appears relatively narrower; interocular space on vertex markedly broad as originally described for the genus, on the average slightly narrower in 33 (2,32—2,68 mm) than in ♀♀ (2,4-2,72 mm), vertex not much sunk in, the central ocellar ridge also ends on vertex in a fairly deep sulcus as described for the type-species of the genus, the boss-like part on each side however less conspicuously prominent; antennae (cf. Fig. 1A ) distinctly much shorter than interocular space, joint 1 thickened, about 1 % to nearly 3 times length of 2, joint 3 stout, columnar, about, to even slightly more than, twice length of 1 and 2 combined, much shorter than club, its apical part broadened, the club itself nearly or about 1 % times as long as joint 3, subspindle-shaped, especially in side view, thickest just before to about the middle, covered with a faint, but distinct, brassy pruinescence or tomentum, except on sensory area, with a belt of minute, spine-like hairs around the thickest middle part and across this part also a few longer, gleaming hairs mainly across the inner, upper and outer sides, especially in ♀♀, with the distinctly-demarcated sensory area, in more or less apical half below, large, elongate- ovate and bordered, ending apically in the crater-like terminal prominence lodging a minute stylet; proboscis ( Fig. 1B ) relatively long, slender, somewhat variable in length, about 2—2,6 mm (the latter when fully extended), on the whole slightly shorter than antennae, with a few, scarcely discernible, hairs along lower part on each side, at least in ♀, its labella short, oval, the apex bluntly rounded, sometimes appearíng obliquely subtruncated; palps small, subglobular.

Wings comparatively short, not reaching tip of abdomen, entirely and markedly transparent, with a faint milky white tint in certain lights; veins white and transparent, only the extreme base of wings, costal vein and to a certain extent second vein slightly yellowish; venation like that of Afroleptomydas; first posterior cell obtusangular apically, either angular and shortly stalked apically or narrowly opening apically on second vein; second submarginal cell with an appendix basally; discoidal cell acute and shortly stalked apically; axillary lobe and alula moderately developed; halteres whitish.

Legs rather short, slender, the femora in 33 slightly thicker than in ♀♀, the hind ones in ♀♂ longer, but in ♂♂ very slightly more thickened, the legs in ♂♂ distinctly more densely hairy; femora in ♂♂ with only dense long and short hairs below, no distinct spines being discernible, even on hind ones below; femora in ♀♀ also with long and short hairs, more above than below, but much fewer and less dense than in 55, the front and middle ones without any detectable spines below, the hind ones less hairy, mainly short-haired above, with comparatively only a few long ones basally above and, in addition to a row of long bristly hairs along inner side below, with more or less two irregular rows of comparatively short, slender, white, bristle-like spines, as well as irregularly disposed, shorter, spine-like setae or seta-like spinelets below; tibiae curved in both sexes, the hind ones so near apex, hairy in both sexes, but more densely and to a certain extent longer so in ♂♂, especially the hind ones in latter sex with dense long and shorter hairs, with the front and middle tibiae in ♂♂ armed below with fine hair-like or bristle-like spicules, these in ♀♀ very slightly thicker, and hind tibiae in ♀♀ with stouter and more distinct spicules; apical spicules or spurs of tibiae below well developed, fairly long, golden yellow, equally developed in both sexes; tarsi with the spicules below, especially on hind ones, also well developed and golden yellow; claws in ♂♂ longer, more developed than in ♀♀; pulvilli in ♀♀ shorter and less developed than in ♂♂.

Hypopygial complex of 5 ( Fig. 1C-D ) with tergite 8 sometimes exposed as a short half-moon-shaped posterior part, depending on the upward or downward movements 0f the hypopygium, its projecting lateral lobe on each side of base of sternite 9 lobe-like; sternite 7 with only its hindermost part exposed, being almost entirely pushed forwards by base of sternite 9, its exposure or conceal- ment being due to the upward, downward and forward movements of the hypopygium; hypopygium itself large and conspicuous as described for the genus ( Hesse 1972; 160), in form of an oval box-like structure in side view, tergite 9 and anal lobes constituting a sort of fixed lid, the tergite itself about l,6- l,8 mm long, convex, deeply and angularly incised posteriorly in which the anal lobes are situated, basally slightly transversely depressed above and on sides basally firmly and immovably united by a shining, weal-like, strongly- chitinized connection on each side dorsally to sternite 9, and which also constitutes the base of the prong on each side of the latter sternite; sternite 9 large, navicular, about 2,72—2,8 mm long, compressed from side to side, the strongly-chitinized keel of the ‘boat’ being than the sides above, more narrower posteriorly the sternite is deeply and angularly incised V-like; upper chitinized and ridge-like side ‘gunwale’ of this boat-like sternite is continued or posteriorly as a lateral flange to form the posteriorly projecting, flattened, down- wardly-directed, tongue-shaped process or prong on each side, the upper posterior of the ‘ gunwale’, which also constitutes the part upper part or corner of the V-shaped incision on each side, is prominent, rounded, strongly chitinized, shiny, and connected with the lateral prong, the less chitinized, paler sides of the sternite with long white hairs which are directed downwards posteriorly on each side of incised part; keel of sternite 9 is flattened, strongly chitinized, brown, and lodges the long, double-tubular aedeagus; aedeagus itself remarkably long, in form of a long, curved, double-tubular organ, composed of two parallel adherent tubes, thicker basally than posteriorly and lodged in the keel-part of sternite 9, bending forwards posteriorly just inside the posterior V-shaped incised part of the sternite and there becoming separated as two separate, thinner, aedeagal branches, each ending in a gonopore; epimere, as far as this can be seen, in form of a flattened bluntly-forked or bifid structure anterior to the aedeagal branches of aedeagus and pointing slightly backwards. The process of copulation, though not observed by the collectors, probably takes place end to end as in Asilidae . In this case both the aedeagal tubes and the forked epimere are probably pushed backwards or posteriorly through the posterior V-shaped incision of sternite 9 to engage the genital organs of the 2 in which they are also aided by the posterior lateral processes of the sternite which probably act as hooking structures. Genital. vøgmenrs of 2 structurally more or less as described and figured for the genus ( Hesse 1972: 161, 164); hood-like tergite 8 with its hind margin slightly produced medially, there rounded and carinate, the disc transversely coarsely striate and punctured, more coarsely punctured intramarginally posteriorly; acanthophorites each with about 7 flattened, apically slightly broadened, yellowish spines, the first one at the base being more slender and rod-like; anal lobes with dense, short, stitï hairs or setae; sternite 8 half hidden, its hind margin emarginate or indented and its sides slightly rugose.

From 1 ♂ holotype, 1 ♀ allotype, 3 ♂ paratypes and 3 ♀ paratypes in the South African Museum.

Distribution

South-western Cape: Paternoster (A. J. Prins, 13 February 1973) (♂ holotype, ♀ allotype, ♀ paratype, and 3 ♂ paratypes); Paternoster (V. Branco, 13 February 1973) (2 ♀ paratypes).

Compared with the type-species gaerdesi Hesse ( Hesse 1972: 161) from the Namib Desert, this new species may at once be dístinguished by its much smaller size, relatively shorter, more slender legs, comparatively denser and entirely white vestiture in ♂♂, distinctly very much shorter or minute hairs on abdomen above in ♀♀, hairs on metanotum confined to sides, joint 3 of antennae proportionally longer relative to the other joints, much shorter and relatively less slender proboscis which is slightly shorter, not longer, than antennae and with a more bluntly-rounded apex of labella, the finer and more numerous spines and spinelets on hind femora below, especially in ♀♀, comparatively shorter apical spurs on tibiae, the more boat-shaped, not Argonauta-shell-shaped, sternite 9 of the ♂ hypopygium, the broader, more lobe-shaped lateral appendages of the half-concealed tergite 8, the more rounded upper corners of posterior V-shaped incision of sternite 9 which is not fused with lower part of posterior lateral lobes of tergite 9, the fewer (only about 6 or 7, not 8) spines on acanthophorites of ♀♀, and the less sharply or deeply indented hind margin of the half-concealed sternite 8 in ♀♀.

Figures

Fig. 1. Namibimydas prinsi sp. nov. A. Side view of left antenna of ♀ allotype. B. Side view of proboscis of ♀ allotype. C. Posterior view of hypopygium of ♂ (vestiture partially omitted to show some structures more clearly). D. Right side view of the partially extruded hypopygium of a d‘. (AE = the characteristically long, curved aedeagus lodged in the keel part of sternite 9; AL = anal lobes; Ap 2 appendage of concealed or semi-concealed segment 8; Ep I epimere; IX.S. = large boat- or shell-shaped sternite 9; IX.T. = lid-like tergite 9, immovably attached to sternite 9; Pr I processes of sternite 9; VII. T. = tergite 7 partially or entirely covering tergite 8.)