Daspletis vespertilio ( Engel, 1932 ) Londt, 2010

Londt, Jason G. H., 2010, A review of Daspletis Loew, 1858 with the addition of a remarkable South African species (Diptera: Asilidae: Stenopogoninae), African Invertebrates 51 (1), pp. 183-183 : 185-190

Daspletis vespertilio ( Engel, 1932) comb. n.

Figs 1–12 , 14

Microstylum hermanni var. vespertilio Engel, 1932: 267 .

Microstylum vespertilio: Oldroyd, 1980: 365 .

Engel’s (1932) description of vespertilio , ascribed to Hermann, which follows his listing of Microstylum hermanni , is short and here reproduced for direct comparison with a full redescription:

Hermanni vespertilio Herm. in litt. var. nov.

In the collection of the late Prof. Hermann is the ơ of a very dark variety, under the name from Henkries, Bushmanland (Lightfoot).

The wings are very broad and brown, with lighter spots in the cells of posterior margin, and closed cell R 5. The femora of all legs and all bristles of body are black, also those of mystax.

Occiput, pronotum and mesonotum with dirty yellowish hairs. The designs on mesonotum are identical with such in Hermanni, and the whitish middle stripe very conspicuous. The pubescence of abdomen black.

Length of body 30 mm.; length of wing 25 mm.; breadth of wing 8 mm.

Redescription: I have not studied Engel’s holotype specimen (listed below), apart for seeing a series of digital photographs sent to me for comparison with the recently collected material, upon which this redescription is based. These descriptive passages are based primarily on the male specimens in NMSA, although notes on sexual dimorphism are also provided. Standard abbreviations are used, chiefly in accordance with McAlpine (1981) .

Head ( Fig. 2 ): Dark red-brown to black, extensively black setose. Face, frons, vertex and occiput grey-red pruinose. Antenna: Scape and pedicel cylindrical, strongly black setose (especially ventral aspect of scape). Postpedicel slightly clavate, asetose except for a few minute dorsal setulae. Style not discernible, postpedicel terminating in obliquely angled pit enclosing a sensory spine-like element. Segmental proportions 1:0.6:3.0. Face with prominent ventral swelling with clearly demarcated dorsal region, occupying three quarters of facial profile. Mystax black, composed of both robust and more slender setae, confined to facial swelling. Frons and vertex black setose; ocellar tubercle with 2 proclinate macrosetae accompanied by some smaller setae. Occipital setae mostly black except for a number of shortish, slightly curved, pale yellow macrosetae dorsocentrally.

Palpi 2-segmented, cylindrical, entirely black setose. Proboscis long, straight, black setose basoventrally, with a group of small pale yellow setulae at tip.

Thorax: Dark red-brown to black except for orange-brown postpronotal lobes. Black setose, except for a few pale yellow-white antepronotal macrosetae and a few small white setae; entirely dull reddish grey pruinose (although parts are only weakly so). Mesonotum with a pair of dorsolongitudinal dark stripes (caused by weak pruinescence). Mesonotal setae mostly black (some small, pale yellow and white setae occur posteriorly). Macrosetae: Acrostichals absent. Dorsocentrals well developed black, extending full length of mesonotum. Postpronotals well developed, 2 posthumerals, 4 notopleurals, 4 supra-alars, 4 postalars. Scutellum entirely dull grey-red pruinose, disc weakly setose, 6 black apical scutellars. Pleura uniformly grey-red pruinose, fine black setose except for ca 6 black katatergal macrosetae.Anatergites black setose. Halteres dark red-brown with slightly orange base. Legs: Slender, dark red-brown to black (distal parts of prothoracic femora and proximal parts of tibiae may be are slightly orange), bases of claws orange-brown, pulvilli brown-orange. All setae dark red-brown to black. Claws about as long as tarsomere 5, empodia as long as claws, pulvilli about three quarters length of claws. Wings: Length (measured from humeral vein to tip) ranges from 25.0– 26.6 mm (– x=26.1, n=6), breadth (measured at widest level) ranges from 8.4–9.6 mm (– x= 8.9 mm, n=6). Venation ( Fig. 3 ): Cells r 5 and m 3 closed and stalked (M 2 and M 3 may show traces of rudimentary ‘crossveins’), cup may be narrowly open on wing margin or closed on wing margin (but never stalked). Membrane almost entirely blackish stained, central parts of some cells being only weakly-stained (largest specimen demonstrates the least degree of staining), microtrichia not evident.

Abdomen: Dark red-brown to black, hind margins of T2–5 slightly brownish. Segments 1–7 entirely dull reddish pruinose, terminalia apruinose. T1 with some black macrosetae laterally, other terga with tiny black setulae only. Sterna (S) with longish, fine, black setulae. Terminalia ( Figs 5–7 – illustrated genitalia are those of a specimen preserved in 96 % ethanol): Rotated clockwise through 180°. S8 well developed, slightly indented posteromedially and with somewhat undulating hind margin. Epandrial lobes simple, in ‘dorsal’ view ( Fig. 6 ) deeply incised medially resulting in two lobes, weakly attached basally, in lateral view lobes project distally slightly beyond levels attained by other genital components. Proctiger simple, cerci deeply incised medially with weakly sclerotized basal parts. Gonocoxite well developed, distal end somewhat truncate (lateral view) and broadly bifurcate (ventral view); gonostyle well developed, curved toward epandrium (lateral view). Hypandrium well developed, in ventral view ( Fig. 7 ) broad proximally, tapering fairly rapidly to narrowly-rounded distal lobe; laterally, hypandrial lobe almost parallel sided (although somewhat laterally compressed and consequently appearing paler in colour than surrounding structures), with smoothly rounded distal end. (Note: Londt (1983) incorrectly referred to the hypandrium as ‘fused gonocoxites’.)

Description of female: While females ( Fig. 1 ) share many features with males, there is significant sexual dimorphism, especially with respect to the coloration, size and shape of wings. For this reason the following notes relating to females are provided.

Head: Orange-brown to dark red-brown, macrosetae predominantly yellowish, smaller setae white (a few black setae may occur on scape, vertex, occelar tubercle and palpal tip). Antenna: Red-brown, white setose (some macrosetae situated ventrally on scape may be yellowish or dark brown). Mystax and occiput with yellowish macrosetae accompanied by smaller white setae.

Thorax: Less extensively dark red-brown when compared to males, posterior parts of mesonotum somewhat orange. Some pleura (e.g. katepisternum) somewhat orange. Setae mostly fine white, macrosetae yellowish except for dorsocentrals and some laterally situated macrosetae that may be black (there is great variation and no pattern can be established). Scutellar macrosetae also variable in colour, being either yellow or black. Haltere yellow with darker stalk. Legs: Mostly dark red-brown (prothoracic femora and tibiae may be somewhat orange).Almost all minor setae white, macrosetae variable white or dark red-brown. Wings: Mean length (L) and breadth (B) 17.6× 5.7 mm (n=6). Female wings shorter and narrower (L/B=3.1) than in males (L/B=2.7). Venation ( Fig. 4 ) similar to males, but little or no remnants of ‘crossveins’ on veins M 2 and M 3. Membrane transparent, almost entirely lacking staining except narrowly along interior cell margins (this slight staining gives veins a characteristic ‘shaded’ appearance).

Abdomen: Dark red-brown, but posterior margins of terga (T) somewhat orange. Apart from yellow macrosetae laterally on T1 all terga minutely white setose. Except for setae of T1 and anterolateral parts of T2 all abdominal setae directed anteriorly. Terminalia ( Figs 8–10 ): T8 (epigynium) well developed, T9 not evident (reduced and membranous or fused with T10), T10 (acanthophorites) well developed, divided into two halves medially, each half bearing 5 well developed, dorsoventrally compressed macrosetae; cerci broad, well developed, fairly broadly fused basally. S8 (hypogynium) broadly rounded posteriorly, distally broad with medially incised anterior region.Three swollen, bladder-like spermathecal reservoirs visible on dissection, each with a long, narrow, weakly sclerotized duct ( Fig. 10 ) (details of all internal structures could not be clearly seen).

Holotype: SOUTH AFRICA: ơ ‘Bushmanld. [Bushmanland] / Henkries [28°58'S: 18°09'E]. / Lightfoot’ [White], ‘Sammlung / F. Hermann’, [Red label without writing], ‘Capland / Microstylum / vespertilio / Type Hrm [Hermann]’ [Pink with black frame], ‘ Microstylum / vespertilio ơ / Hrm. [Hermann] / det. E.O. Engel’ [White with black frame] [SMNS]. Note: Digital photographs show that the unique holotype is in excellent condition and that new material is conspecific.

New material: SOUTH AFRICA: 6ơ 4^‘South Africa: N Cape / 11km SW Aggeneys 785m / 29°18.26'S: 18°47.85'E / J.G.H. Londt & T. Dikow / 3.x.2009 Red dune. Grass / & woody vegetation’ (NMSA); 7ơ 4^‘South Africa, Northern Cape, / 11 km SW Aggeneys N14, 785 / m, 29°18'04''S 018°47'27''E, / 3.x.2009, T. Dikow & J. Londt, / red vegetated sand dune (at / powerline crossing)’ (FMNH); 2^‘South Africa: N Cape / ca 5 km S of Pella 570 m / 29°04.38'S: 19°08.19'E / J.G.H. Londt & T. Dikow / 3.x.2009 Red sand dune / Dry grass & bushes’ (NMSA). Note: Although all the Aggeneys material was collected on the same occasion, the FMNH specimens, which are slightly differently labelled, were not available to me when the redescription was drafted. There is, however, no doubt that these are correctly assigned to this taxon. In addition, the following specimens were also obtained and are available for DNA sequencing and dissection: 1ơ 1^in 95% ethanol (Dikow coll.), 1ơ 2^Kahle’s solution (Dikow coll.), 1ơ in 95% ethanol (NMSA). Comparison: Species of Daspletis can be segregated into two species groups (see key – couplet 2). D. vespertilio clearly belongs to the hermanni group by virtue of its short dorsal occipital macrosetae, lack of macrosetae on abdominal terga (other than T1), and generally slender abdomen. In these respects vespertilio differs from species in the vulpes group ( hirtus , placades, stenoura and vulpes ). Although the males of vespertilio share the feature of darkly stained wings possessed by both hermanni and lykos their wings are much blacker and larger than in these species. Species in the hermanni group also share similar male genital characteristics (as do those in the vulpes group). The similarities are best appreciated through a comparison of published illustrations. The illustrations of the terminalia of vespertilio provided in this paper ( Figs 5–7 ) should be compared with those of hermanni (figs 8–10 in Londt (1983)), setithoracicus (figs 19– 21 in Londt (1983)) and lykos (figs 1–3 in Londt (1985)). Perhaps the most obvious differences displayed by vespertilio males are to be found in the somewhat reduced hypandrium which lacks the broad appearance of the laterally compressed distal lobe seen in the other species.

Distribution ( Fig. 14 ), phenology (Table 1) and biology: D. vespertilio has only been collected at three localities.The date of collection has not been recorded for the holotype, while all the other specimens were collected early in October. Both newly recorded sites were similar in that they feature poorly vegetated and fairly extensive red sand dune systems ( Fig. 12 ).Although little biological information is available, some insights may be inferred from field observations made by both Dr Dikow and me, as well as from their general morphology. Male individuals were first encountered after they had been disturbed and had taken to flight. Their highly characteristic, fairly slow, flapping flight was intriguing and reminiscent of some large antlions (e.g., species of Palpares ). When pursued, often over considerable distances, they appeared to take evasive action by flying in an erratic manner. The fact that vespertilio males have large, broad, black, and therefore highly visible wings (as well as a long, slender, stabilizing abdomen), when compared with many other asilids, and that their flight is slow but sustained, strongly suggests that they probably perform an aerial display, presumably designed to attract the attention of females. Aerial displays are fairly well documented for Asilidae and include a number of species within the Stenopogoninae ( Lavigne 2003) . Females, with their smaller, narrower, and almost transparent wings, flew more rapidly, and in a relatively unsustained manner when compared with their male counterparts. Both sexes rested on the ground, wings folded one upon the other over their abdomens, and with their legs outstretched ( Fig. 11 ).

Meteorological data indicate that much of the Northern Cape, including the localities recorded for vespertilio , receives most of its rain between February and April, and virtually no rain falls between July and October. D. vespertilio , therefore, flies at a time when the vegetation is parched and relatively little invertebrate life is evident. This probably accounts, in part, for the fact that this large species has been overlooked until now. Temperatures during October may be cool at night and relatively mild during the day. The dark coloration of males is almost certainly an adaptation to generally cool weather conditions and is reminiscent of insects associated with the winter rainfall areas of the Western Cape. This is in stark contrast with species in the vulpes species group ( hirtus , placodes , stenoura and vulpes ) that are mostly late summer active, and pale yellowish in colour.

Annotated checklist of other Daspletis species

Londt’s (1983) revision of Daspletis was based on 139 listed specimens, a further three being added with the description of lykos (Londt 1985) . In order to more adequately define the distributions of the species, I list below all the material known to me, previously recorded and new (amounting to 317 specimens), and provide comments concerning distribution, phenology and biology of each species.

Figures

Figs 1–4. Daspletis vespertilio (Engel, 1932): (1) entire male (left) and female (right) showing size and general appearance of the two sexes, scale bar in mm; (2) head; (3) wing of male preserved in ethanol (staining not as extensive as in most other males); (4) female wing.See text for measurements.

Figs 5–10. Daspletis vespertilio (Engel, 1932) terminalia: (5–7) male, preserved in ethanol: (5) lateral, (6) dorsal, (7) ventral; (8–10) female:(8) dorsal, (9) ventral, (10) spermathecal reservoir.Scale = 1 mm.

Figs 11, 12. Daspletis vespertilio (Engel, 1932): (11) male resting on red sand, (12) general view of habitat type, 5 km S Pella.

Fig. 14. The distribution of Daspletis Loew, 1858 species in southern Africa: hirtus (circles), setithoracicus (squares), vespertilio (triangles), vulpes (diamonds).