A review of the genus Gibbasilus Londt , 1986 in southern Africa ( Diptera , Asilidae )

Gibbasilus Londt, 1986, a small genus of asiline Asilidae endemic to the Western Cape Province of South Africa, is taxonomically revised. Three species are described for the first time (alboala, condylus, crinitus) and added to those already known (arenaceus, brevicolis, centrolobus). A key for the identification of species is provided. Little is known of their biology, but a close association with species of Restionaceae, a dominant element of the Cape Floristic Region, has been observed. It is suspected that females, which possess long, laterally compressed, knife-like ovipositors, use these plants as oviposition sites.


Introduction
The acquisition of interesting new material representative of the distinctive South African asilid genus Gibbasilus Londt, 1986, gave rise to the need to provide a new taxonomic perspective on the genus whose history is brief and can be summarised as follows: Londt (1986) -Described Gibbasilus and type species (arenaceus) using material collected from the Western Cape Province of South Africa.Londt (1990) -Added a further two Western Cape species to the genus (brevicolis, centrolobus).Londt (2005) -Discussed the genus and included it in a key to Afrotropical Apocleinae (now considered part of the subfamily Asilinae).
At the commencement of this study there were therefore only three species included in the genus.New material which has been incorporated into the KwaZulu-Natal Museum's, collection over the last 25 years allows a further three species to be described.All are to be found in a relatively small region of the Western Cape Province of South Africa.

Material and methods
Much of the material previously recorded by Londt (1986Londt ( , 1990) ) has been re-examined and included in the lists of material supplied for each species and marked with either an asterisk (*) for 1986 material or a crosshatch (#) for 1990 published material.While a few specimens are housed in other collections, the vast majority are stored in the KwaZulu-Natal Museum (NMSA), Pietermaritzburg.Other institutional abbreviations used in this paper are: BMNH (The Natural History Museum, London, U.K.) and SAM (Iziko South African Museum, Cape Town, South Africa).Label data is cited as it appears on labels, lines of data being separated by a slash (/).While more recently collected specimens are usually provided with detailed information relating to locality and habitat, it has been necessary to attempt to establish precise geographic coordinates for older or poorly documented material in order to gain a better appreciation of the distribution.Google Earth and the Internet have been used to accomplish this.All information not supplied on labels appears in square brackets.
Illustrations provided are designed to complement those of Londt (1986Londt ( , 1990) which should be consulted when comparisons are made.Male terminalia were excised and cleared in heated Potassium Hydroxide (KOH) before being drawn with the aid of a drawing tube.Female terminalia were not excised for illustration.Standard abbreviations and terminology are used, chiefly in accordance with McAlpine (1981).
Diagnosis (modified from Londt 1986).Asiline flies displaying the following combination of characters.Head: Face plane, not gently convex; dorsal occipital macrosetae long, proclinate.Thorax: Mesonotum strongly humped; acrostichal setae long, well developed, tightly packed and arranged in a narrow strip; scutellum with a single pair of apical scutellar macrosetae; discal cell (1m 2 ) of wing not markedly constricted at midlength (as in Synolcus Loew, 1858); male wing with costal region not markedly expanded (as in some Dasophrys Loew, 1858).Abdomen: Female ovipositor long (more than twice as long as broad in lateral aspect) and laterally compressed.Figure 1 illustrates a fairly typical male of the genus.
Abdomen: Entirely dark red-brown to black, extensively dull silver pruinose, except lateral margins of T2 and T3 which are shiny apruinose.Terga fine short white setose, T1-4 with 1-2 laterally situated pale yellow macrosetae (progressively diminishing in size towards terminalia).Sterna fine, longish setose.♂ genitalia (Figs 3-6): Epandrium about three times longer than deep in lateral view, with widest part proximal to midlength; moderately broadly rounded distally; lobes gradually diverging distally in dorsal view.Gonocoxite not quite ⅓ as long as epandrium, smoothly rounded distally.Gonostylus elongate, almost half the length of epandrium, of approximately same width for entire length in ventral view, distally with a subtriangular upwardly directed process, best appreciated in lateral view.Hypandrium short, almost three times wider than long in ventral view, distal margin very slightly indented medially.Aedeagus long and thin, slightly dorsoventrally compressed, S-shaped distally, terminating in a 3-pronged tip.Posterior margin of S8 slightly indented medially with a terminal, subrectangular, dorsoventrally compressed process projecting to approximately midlength of hypandrium.♀ unknown.
Remarks.This species bears a strong resemblance to condylus sp.n., described below, but is immediately recognised by the milky white bases to the wings.This condition, although unique within Gibbasilus, is encountered in other asilid genera such as Hypenetes Loew, 1858 (Londt 1985).While it remains possible that the possession of milky wing bases is a variable character I consider alboala and condylus to represent separate taxa until shown otherwise.In the absence of females it is not known if milky wing bases are confined to males.
Distribution (Fig. 20B), phenology (Table 1) and biology.Known only from the type locality.Collected in November.The general habitat consisted of endemic fynbos plant species and large boulders.
Description.The species was fully described by Londt (1986) who provided illustrations of the general habitus, antenna, wing, ♂ terminalia, ♀ ovipositor and pupa as indicated above.The species bears a strong resemblance to the newly described crinitus sp.n. (see below).A new illustration of the ♀ ovipositor is here provided for comparative purposes (Fig. 7).The length : depth ratio of the ovipositor = 4.0 : 1. Remarks.This species bears a strong resemblance to crinitus sp.n., described below, but can be separated from that species on features of the male terminalia (inn particular the poorly developed pale setae found along the posterior margin of S8).
Distribution (Fig. 20A), phenology (Table 1) and biology.Known from six localities approximately centred on the towns of Vanrhynsdorp and Clanwilliam.Collected during the months of September, October and November.Specimens collected by me 22 km south of Vanrhynsdorp, on the road to the Gifberg, were found perching near the tops of the vertical stems of a tall unidentified plant species belonging to the family Restionaceae growing on the edge of an old ploughed field (31°46'16"S, 18°45'56"E 545 m).Although oviposition was not observed, it is probable that females use their knife-like ovipositors to insert eggs into suitable crevices found on these plants.Description.The species was fully described by Londt (1990), based on the unique holotype ♂.Illustrations were provided of the wing and ♂ terminalia.No new material is available and the ♀ remains unknown.The species cannot be confused with other species, having distinctive ♂ terminalia.Material examined.SOUTH AFRICA: 1♂ holotype "Pakhuis Pass [c.32°08'S, 19°02'E 635 m], C.P. S. A.M., 9:1961 [ix.1961]" (SAM).
Distribution (Fig. 20B), phenology (Table 1) and biology.Known only from the type locality of Pakhuis Pass, a road to the east of Clanwilliam leading to the Biedouw Valley.Collected in September.No biological information is available.The pass is rocky and dominated by indigenous fynbos.
Description.The species was described by Londt (1990), based on a unique holotype ♂ specimen, and both the wing and ♂ terminalia were well illustrated.On re-examination it has been found that two paratypes of arenaceus, 1♀ and 1(sex unknown) lacking terminalia, listed below, were not conspecific and have been reallocated to centrolobus.The ♀ ovipositor (which is glued to the pin beneath the specimen) is here illustrated (Fig. 8), its length : depth ratio = 3.6 : 1.These specimens appear to be correctly allocated to centrolobus as the wings are microtrichose and the only pale mystacal macrosetae are restricted to the epistomal margin.The ♂ of this species cannot be confused with other species as it has distinctive terminalia.
Abdomen: Entirely dark red-brown to black, extensively dull silver pruinose, except lateral margins of T2-5 and parts of S2-2 which are shiny apruinose.Terga fine short white setose except for narrow medial strip of fine black setae, T1-6 with 1-3 laterally situated pale yellow macrosetae (progressively diminishing in size and number towards terminalia).Sterna fine, longish setose.♂ genitalia (Figs 11-14): Epandrium almost three times longer than deep in lateral view, with widest part proximal to mid-length; not very broadly rounded distally; lobes gradually diverging distally in dorsal view.Gonocoxite almost ⅓ as long as epandrium, smoothly rounded distally.Gonostylus elongate, almost half the length of epandrium, of approximately same width for entire length in ventral view, distally with a subtriangular upwardly directed process, best appreciated in lateral view.Hypandrium short, about four times as wide as long in ventral view, distal margin very slightly indented medially.Aedeagus long and thin, slightly dorsoventrally compressed, S-shaped distally, terminating in a 3-pronged tip.Posterior margin of S8 slightly indented medially with a terminal subrectangular, dorsoventrally compressed process projecting to approximately midlength of hypandrium.♀ ovipositor (Fig. 9): Elongate, laterally compressed and knife-like.Length : depth ratio = 2.7 : 1 (more robust when compared with other species).Remarks.As mentioned earlier, this species bears a strong resemblance to alboala sp.n. (described above), but can easily be separated from that species as it has entirely transparent wing membranes, lacking the somewhat opaque, milky basal wing membranes diagnostic for alboala.
Distribution (Fig. 20B), phenology (Table 1) and biology.Known from four fairly widely separated localities.Collected during the months of October and November.Specimens collected by me, at three localities, were found perching near the tops of the vertical stems of a tall unidentified species belonging to the Restionaceae or sunning themselves on stones.A typical habitat at the Kagga Kamma Nature Reserve is illustrated (Fig. 15).Although oviposition was not observed, it is probable that females use their knife-like ovipositors to insert eggs into suitable crevices found on these plants.The species is found sympatrically with crinitus.Description.Based on type series consisting of 5♂ 3♀.Head: Black, fine silver pruinose, black and white setose.Antenna: Black, fine silver pruinose, scape and pedicel black setose.Segmental ratios (scape as 1) = 1 : 0.6 : 1.5 : 0.7 (elements of style = 0.2, 0.4, 0.1).Style composed of three elements (small basal segment-like element, long middle rod-like element, terminal seta-like sensory element).Face black, silver pruinose, profile plane.Mystax long, well-developed, extending from epistomal margin to antennal sockets, macrosetae black (laterally) and white (centrally) down entire depth of face.Frons and vertex black, weakly silver pruinose, fine, long, black setose.Ocellar tubercle with long, fine, black setae.Postocular (occipital) region black, silver pruinose, mostly black setose dorsally, white laterally and ventrally.Palpi 2-segmented, segment 1 white setose, 2 black setose.Proboscis shiny black, fine white setose.
Abdomen: Entirely dark red-brown to black, extensively dull silver pruinose, weakly along lateral margins of T2-4 and S2-4 which are shiny apruinose.Terga fine short white setose except for narrow mid-dorsal strip of tiny black setae, T1-5 with 2-3 laterally situated pale yellow, weak macrosetae (progressively diminishing in size towards terminalia).Sterna fine, longish setose.Remarks.This species bears a strong resemblance to arenaceus, but can be separated from that species on features of the male terminalia (mainly on the well-developed black setae found along the posterior margin of S8).While crinitus sp.n. may

Discussion
Taxonomy: With the description of three new species, Gibbasilus is now represented by six species.With the discovery that only three of these possess microtrichose wing membranes the genus can be split into two groups as demonstrated in the key.Females are now known for four species and it is of interest that all those with microtrichose wings (arenaceus, centrolobus, crinitus) possess slender ovipositors (length : depth ratios ranging from 3.64.7 -1).G. condylus, on the other hand, has a more robust ovipositor (length : depth ratio of 2.7 : 1) which might suggest that when females of alboala and brevicolis are discovered that these too will possess fairly robust ovipositors.Distribution and biology: Gibbasilus is confined to a rather small region of the Western Cape Province of South Africa (Fig. 20).Adult activity appears to be confined to the spring months of September through to November (Table 1) in this winter rainfall region of southern Africa.The majority of known localities appear to have a number of things in common -relatively high altitudes, rocky outcrops and a habitat dominated by plants belonging to the family Restionaceae, an important defining family within the Cape Floristic Region's, fynbos plant community (Linder et al. 2003).Apart from a few individuals being found sunning themselves on rocks, virtually all specimens collected by me were resting on the stems of tall restios (often on the higher stems).This might suggest that females are adapted to oviposit on these specific plants.It can, therefore, be confidently predicted that Gibbasilus may well be a far more dominant group of asilids than available records suggest.

Table 1 .
Phenology of Gibbasilus species.Months, starting at July, abbreviated as shown.