Review of the genus Namadytes Hesse, 1969 (Insecta: Diptera: Mydidae: Syllegomydinae)

Abstract The Mydidae genus Namadytes Hesse, 1969 is reviewed. It is known from five species, primarily occurring in Namibia. The study of newly available material from both Namibia and South Africa deposited in several natural history collections results in the recognition of three species and new synonymy of two, i.e., Namadytes pallidus Hesse, 1972 is a new junior synonym of Namadytes maculiventris (Hesse, 1969) and Namadytes prozeskyi Hesse, 1969: 282 is a new junior synonym of Namadytes vansoni Hesse, 1969: 280. All three species are re-described and comments on sexual dimorphism and intraspecific variation are made, a dichotomous key for their identification is presented, and illustrations and photographs are provided to support the descriptions and facilitate future identification. Distribution, occurrence in biodiversity hotspots sensu Conservation International, and seasonal incidence with associated weather and climatic data are discussed for all species. A morphological structure ventral to the halter and posterior to the metathoracic spiracle, the infra-halter sclerite, is here newly termed.


Introduction
The southern African Mydidae fauna is the most diverse world-wide both in terms of species numbers and generic diversity. The seminal work by Hesse (1969) on the southern African mydids based primarily on specimens he collected himself throughout western South Africa, in which he described no fewer than 108 new species (106 of which are still valid) and 12 new genera (11 of which are still valid), provided a comprehensive overview of this unique fauna. Hesse (1972) added to the knowledge following the examination of additional material from Namibia (then South-West Africa).

Taxonomic history
At the start of this review, Namadytes Hesse, 1969 is known from five species with an interesting taxonomic history. • Hesse (1969) described the genus Namadytes (p. 278) based on two female specimens and representing two distinct species, i.e., Namadytes vansoni Hesse, 1969: 280 from Seeheim, Namibia and Namadytes prozeskyi Hesse, 1969: 282 from Arechadamab, Namibia. On page 284, Hesse describes the genus Namamydas Hesse, 1969 based on a single male specimen, identified as Namamydas maculiventris Hesse, 1969, collected by himself and his colleagues from the South African Museum (now Iziko South African Museum) at Vioolsdrift on the South African bank of the Orange River, which represents the border with Namibia. Hesse comments on the unique arrangement of the male aedeagal prongs being fused medially in this species. • Hesse (1972) established the synonymy of Namadytes and Namamydas based on the collection of female and male specimens at the Excelsior farm No. 127, Namibia, of a new species, Namadytes cimbebasiensis Hesse, 1972. He writes (p. 139), "The discovery of two additional species of Namadytes from South West Africa, described below, and of which one is represented by both sexes, proves without doubt that the male sex of Namadytes (unknown at the time of description) is identical generically with the male described by me as Namamydas. The latter genus thus falls away as a synonym of Namadytes. " • Bowden (1980) cataloged all five valid Namadytes species.

Goals of this review
As can be seen from the above information, Namadytes and its five species were represented by nine specimens prior to this study. Two species, i.e., N. prozeskyi and N. vansoni, were known from females only, while N. maculiventris and N. pallidus were known only from males, and N. cimbebasiensis from both sexes.
This review is based on an additional 61 specimens from numerous natural history collections accumulated over the past 35 years representing all previously known species.
Such an increase in specimen number, their geographic occurrence expanding the range of the genus considerably, and substantial morphological variation suggested that a few new species might be represented among the material. However, this not the case and to the contrary the number of valid species is reduced to three by synonymy.

Materials and methods
Morphological terminology and abbreviations for setae follows McAlpine (1981), Stuckenberg (1999), Cumming and Wood (2009), Dikow (2009) except for the term 'aedeagal epimere', which is used as described by Hesse (1969) on page 32. Abdominal tergites are abbreviated in the descriptions with 'T', and sternites are abbreviated with 'S'. The terms prothoracic, mesothoracic, and metathoracic are abbreviated 'pro', 'mes', and 'met', respectively. The term pubescence (adjective 'pubescent') refers to the short, fine microtrichia densely covering certain body parts. Other generalized terms follow the Torre-Bueno Glossary of Entomology Nichols (1989). Species descriptions are based on composites of all specimens and not exclusively on the holotype and are compiled from a character matrix of 149 features and 224 character states assembled with Lucid Builder (version 3.5) and eventually exported as natural language descriptions. These species descriptions have been deposited in the DRYAD data depository and can be accessed in XML-format following the SDD (Structure of Descriptive Data) standard. When available, species are fully described in the male sex while females are only described with those features that differ. The structure of terminalia is only described once for the genus except when species differ. Additional species-specific features of the male terminalia should be interpreted from the provided illustrations.
The female genitalia and male terminalia are first excised and macerated in 10% potassium hydroxide (KOH) at 55°C followed by neutralization in acetic acid (CH COOH) and rinsing in distilled water (H O). They are temporarily stored in 75% ethanol (C H OH) for examination and illustration and eventually sealed in polyethylene vials containing 100% glycerine (C H O ) and attached to the specimen's pin. Morphological features were examined using a Zeiss SteREO Discovery.V12 stereo microscope. Illustrations were observed with a camera lucida, drawn, inked, and scanned. The setation on terminalia is not shown. Wing length is measured from the tegula to the distal tip of the wing. Whole habitus photographs of pinned specimens were taken using a Visionary Digital Passport II system (base and StackShot only), an Olympus E-30 digital SLR, a 50 mm macro lens (equivalent to 100 mm focal length in 35 mm photography), and a 25 mm extension tube. The specimens were illuminated by a Falcon FLDM-i200 LED dome-light for even and soft light. Adobe DNG-format images were stacked using HeliconFocus software. Photographs of particular features were taken on a Zeiss SteREO Discovery.V12 stereo microscope and an attached Olympus PEN E-PL5 digital camera. All specimen photographs have been deposited in Morphbank:: Biological Imaging. These images can be automatically harvested by the Encyclopedia of Life (EOL) and are available under the respective species page.
The following data on species occurrences are given (where available): country, state/ province, county, locality, geographic co-ordinates (formatted in both decimal and degrees minutes seconds latitude/longitude), elevation (in meters), date of collection (format: yyyymm-dd), habitat information, sampling protocol (if other than hand netting), collector, catalog number (a unique specimen number and any other identifying number), depository (institution and collection code), number of specimens and sex, life stage, name of person who identified the specimen, and any other previous identifications (note that for synonymized species the holotype still retains its status as a primary type specimen and therefore the particular material examined list will include two (or more) holotypes; see the entry under 'previousIdentifications' for the original identification by the author). Each specimen is listed with a unique specimen number (either an institutional catalog number or an AAM-XXXXXX number used by the senior author) that will allow the re-investigation as well as provide a unique Life Science Identifier (LSID

Diagnosis
The genus (Fig. 3) is distinguished from other Syllegomydinae by the structures of the male genitalia (aedeagal prongs fused medially), the presence of a V-shaped indentation on the dorso-median antepronotum, and the presence of a tuft of setae on the infra-halter sclerite (ventral to halter base and posterior to metathoracic spiracle), with the exception of females of one species. Furthermore, flies are relatively small with a wing length of 6.6-14.2 mm and the males exhibit a yellow to light brown abdomen, which is unusual for southern African Mydidae.

Distribution
Namadytes is distributed in southern Africa and restricted to Namibia and northwesternmost South Africa (Fig. 4).

Taxon discussion
Males are unique in the arrangement of their medially fused aedeagal prongs and the yellow to light brown abdominal coloration. Females in contrast are more generalized and similar to other female Mydidae occurring in southern Africa. However, the anteromedian V-shaped indentation on the antepronotum and the presence of white setae on a b c Figure 2.
Namadytes cimbebasiensis ♂ terminalia (NMNW-H7808). Scale lines = 1 mm. a: lateral b: dorsal c: ventral the infra-halter sclerite are relatively easy to observe and distinguish the females from other Mydidae. There is considerable sexual dimorphism and the setation, for example on the anatergites, is always easier to observe in males. Intra-specific variation in the abdominal coloration, especially in females, is likewise substantial, which probably led Hesse to describe a species twice.    Fig. 5a, b.
Head: brown, in general grey pubescent; width distinctly greater than thorax, interocular distance on vertex larger than at ventral eye margin, vertex between compound eyes ± horizontally straight, medially only slightly below dorsal eye margin, parafacial area about as wide as ½ the width of central facial gibbosity; facial gibbosity distinct, well-developed and discernible in lateral view; mystax yellow, covering entire facial gibbosity; frons not elevated, predominantly apubescent; vertex entirely grey a b c d pubescent; postgena lightly grey pubescent; setation: vertex yellow, frons white or yellow, ocp setae white, pocl macrosetae absent; ocellar triangle apubescent; proboscis light brown, very short, vestigial, knob-like; labellum small, as wide as prementum, as long as prementum, unsclerotized laterally; maxillary palpus cylindrical, yellow, minute.
Antenna: brown, scape and pedicel white setose dorsally and ventrally; postpedicel cylindrical in proximal ½, symmetrically bulbous in distal ½, ≥ 4.0 times as long as combined length of scape and pedicel, asetose; apical seta-like sensory element situated apically in cavity on postpedicel.
Wing: length = 6.6-8.1 mm; hyaline throughout, veins light brown, microtrichia absent; cells r , r , r , m , + cup closed; C terminates at junction with R ; R terminates in R ; R terminates in R ; stump vein (R ) at base of R present, short not reaching R ; R and R widest apart medially; r-m distinct, R and M apart, connected by crossvein; M straight at r-m (not curving anteriorly), M (or M +M ) terminates in R ; CuA and CuA split proximally to m-cu (cell m narrow proximally); M +CuA do not terminate together in C; A undulating, cell a wide, A and wing margin further apart proximally than distally; alula well-developed; halter light yellow. Abdomen: yellow to brown; setation comprised of dense white setae, surface entirely smooth; T1 brown, T2 brown anteriorly and postero-medially, otherwise yellow, T3-7 brown and yellow posteriorly; T1 and anterior ½ of T2 long white setose, remaining T short white setose; T predominantly apubescent; S1-7 light brown; S1 asetose, S2-7 sparsely white setose; S predominantly apubescent; T2-4 parallel-sided and not constricted waist-like; bullae on T2 black, transversely elongate, surface entirely smooth, T2 surface anterior to bullae smooth.
Leg: femur brown; pulvillus reduced, half length of well-developed claw.

Diagnosis
This rather small species (wing length in males 6.6-8.1 mm and in females 9.6-12.7 mm) is distinguished from congeners by the entirely grey pubescent vertex, the short postpedicel (only about 4 times as long as combined length of scape and pedicel), the grey pubescent scutellum, and the few white setae on the infra-halter sclerite, which are absent in some females.

Biology
Habitat: N. cimbebasiensis has recently been collected on dune scrub and in Acacia savanna in the Kgalagadi Transfrontier Park of the Kalahari Desert by J.G.H. Londt.

Taxon discussion
N. cimbebasiensis is very distinct and the smallest species of Namadytes. All specimens, originating from only five collecting events, are either greasy or are not in the best condition so that in particular the pubescence patterns might differ in freshly mounted material.

Biodiversity hotspot
Not known to occur in any of the southern African biodiversity hotspots (Cape Floristic Region, Maputaland-Pondoland-Albany, or Succulent Karoo) (Fig. 6). Map of southern Africa with elevational relief and biodiversity hotspots (in grey) showing distribution of Namadytes cimbebasiensis (red), N. maculiventris (blue), and N. vansoni (yellow). Map data available in Google Earth KML file and also through GBIF (data-set # 5e6acf4c-e913-45fd-8466-5c0b92c322dd).
Leg: yellow to light brown, setation predominantly white; pro, mes, and met coxa lightly white pubescent, long white setose; met trochanter setose medially; femur yellow to light brown, met femur ± cylindrical only slightly wider than pro and mes femur, in distal ½ macrosetose, 1 antero-ventral and 1 postero-ventral row of macrosetae, posteroventrally long white, erect setose with setae arranged in distinct row; pro, mes, and met tibia straight, met tibia cylindrical, ventral keel absent, latero-posteriorly long white, erect setose with setae arranged in distinct row; pro and mes tarsomere 1 longer than tarsomere 2, but less than combined length of tarsomeres 2-3, met tarsomere 1 as long as combined length of tarsomeres 2-4; pulvillus well-developed, as long as welldeveloped claw, and as wide as base of claw; empodium absent.
Wing: length = 9.6-12.2 mm; hyaline throughout, veins light brown, microtrichia absent; cells r , r , r , m , + cup closed; C terminates at junction with R ; R terminates in R ; R terminates in R ; stump vein (R ) at base of R present, short not reaching R ; R and R widest apart medially; r-m distinct, R and M apart, connected by crossvein; M straight at r-m (not curving anteriorly), M (or M +M ) terminates in R ; CuA and CuA split proximally to m-cu (cell m narrow proximally); M +CuA do not terminate together in C; A undulating, cell a wide, A and wing margin further apart proximally than distally; alula well-developed; halter light yellow.

Taxon discussion
Hesse 1972 (p. 148) alludes to the morphological similarity of Namadytes maculiventris and Namadytes pallidus. We regard the differences between the male holotype of N. maculiventris and the male holotype and paratype of N. pallidus as intraspecific variation. So far, only 4 specimens of this species, all males, have been collected in southern Namibia and Vioolsdrift in South Africa.

Biodiversity hotspot
Not known to occur in any of the southern African biodiversity hotspots (Cape Floristic Region, Maputaland-Pondoland-Albany, or Succulent Karoo) (Fig. 6).
Head: brown, in general lightly silver pubescent; width distinctly greater than thorax, interocular distance on vertex larger than at ventral eye margin, vertex between compound eyes ± horizontally straight, medially only slightly below dorsal eye margin, parafacial area about as wide as ½ the width of central facial gibbosity; facial gibbosity distinct, well-developed and discernible in lateral view; mystax white, densely covering entire facial gibbosity; frons not elevated, predominantly apubescent; vertex predominantly apubescent, only lateral margin grey pubescent; postgena lightly grey pubescent; setation: vertex white, frons white, ocp setae white, pocl macrosetae absent; ocellar triangle apubescent; proboscis brown, short, about ½ length of oral cavity; labellum small, as wide as prementum, as long as prementum, unsclerotized laterally; maxillary palpus cylindrical, light brown, minute.
Antenna: brown, scape and pedicel white setose dorsally and ventrally; postpedicel cylindrical in proximal ½, symmetrically bulbous in distal ½, ≥ 7.0 times as long as combined length of scape and pedicel, asetose; apical seta-like sensory element situated apically in cavity on postpedicel.
Leg: light brown to brown, setation predominantly white; pro, mes, and met coxa lightly white pubescent, long white setose; met trochanter setose medially; femur light brown to brown, met femur evenly clubbed in distal 3/4, in distal ½ macrosetose, 1 antero-a b c d Figure 9. ventral and 1 postero-ventral row of macrosetae, postero-ventrally long white, erect setose proximally with setae arranged in distinct row; pro, mes, and met tibia straight, met tibia cylindrical, ventral keel absent, latero-posteriorly long white, erect setose with setae arranged in distinct row; pro and mes tarsomere 1 longer than tarsomere 2, but less than combined length of tarsomeres 2-3, met tarsomere 1 as long as combined length of tarsomeres 2-4; pulvillus well-developed, as long as well-developed claw, and as wide as base of claw; empodium absent.
Wing: length = 7.1-8.9 mm; hyaline throughout, veins brown, microtrichia absent; cells r , r , r , m , R terminates in R ; R terminates in R ; stump vein (R ) at base of R present, short not reaching R ; R and R widest apart medially; r-m distinct, R and M apart, connected by crossvein; M straight at r-m (not curving anteriorly), M (or M +M ) terminates in C; CuA and CuA split proximally to m-cu (cell m narrow proximally); M +CuA do not terminate together in C; A undulating, cell a wide, A and wing margin further apart proximally than distally; alula well-developed; halter light brown.
Antenna: postpedicel ≥ 5.0-≥ 6.0 times as long as combined length of scape and pedicel.

Diagnosis
This large species (wing length in males 7.1-8.9 mm and in females 10.9-14.2 mm) is distinguished from congeners by the wing venation in that cell r is open and therefore M terminates in C (and not in R ), the predominantly apubescent vertex, the short proboscis that is only about half the length of the oral cavity, the long white setose anatergite, and the setose katepimeron.

Biology
Flight behavior: Females of this species (as Namadytes prozeskyi syn. nov.) were observed by Wharton (1982) to have a hop-like flight in contrast to the low-flying males, which show the characteristic rapid gliding flight behavior in order to locate females for mating. A similar observation has recently been made for Namibimydas psamminos Dikow, 2012(Dikow 2012. Oviposition: Females usually oviposited in shallow depressions, such as hoof prints and in particular on the lip of these prints, in the sandy Kuiseb river bed and followed a Mydidae-characteristic oviposition sequence of sand-ovipositing species (for details see Wharton 1982, p. 149). The insertion of the abdomen into the sand took about 9 seconds while the egg-laying with buried abdomen lasted for 6 seconds. The eggs were orange, hyaline, and pear-shaped and measured 2 x 1 mm (length x maximum width).
Habitat: N. vansoni has been collected in riparian vegetation along a dry river bed, in thornveld in a dry river bed, and on barren gravel plains.

Taxon discussion
This species exhibits substantial intra-specific variation (Figs 9,11) and is the most variable species. However, it is also the species known from the most specimens (61 specimens in total) and has the largest geographic range. Prior to this study, Namadytes vansoni is only known from the sole female holotype (Fig. 9c, d). Only through female and male specimens collected during a single collecting event is it possible to associate both sexes and hence appreciate the pronounced sexual dimorphism (Figs 9a, c, 11). Hesse (1969) hints in the description of Namadytes prozeskyi, which is also only known from a single female holotype, at the similarity to Namadytes vansoni and while he provides quite a few minor differences, we attribute these to intra-specific variation. With the increased number of specimens available in our study, we cannot differentiate the two species and therefore synonymize Namadytes prozeskyi (described on page 282) with Namadytes vansoni (described on page 280) by page priority.

Key to Namadytes species
There is considerable sexual dimorphism and the setation, for example on the anatergites, is always easier to observe in males. Intraspecific variation in the abdominal coloration, especially in females, is likewise substantial.

Morphological characteristics
Namadytes species exhibit two remarkable morphological characteristics unknown in any other Mydidae genus.
• The antepronotum is anteriorly not entire as in all Mydidae, but has a V-shaped indentation medially that is easily visible (Fig. 12a). • A small sclerite ventral to the halter and posterior to the metathoracic spiracle, here termed the infra-halter sclerite (Fig. 12b, c), is unique within Mydidae. This sclerite is usually long, densely white setose, but only sparsely white setose N. cimbebasiensis males and sometimes even asetose in females of this species.

Biology
The knowlegde of the biology of Namadytes is very scarce as there is hardly any information on habitat preferences or flight behavior available on collecting labels. However, Wharton (1982) provided some information on Namadytes vansoni (as Namadytes prozeskyi syn. nov.) based on his year-long study of Mydidae at the Gobabeb Research and Training Centre in the central Namib Desert, which is summarized under the biology section of that species.
Although not directly observed by Wharton, he suggests that mating with teneral or very young females might occur in Namadytes as well and is an important adaptation for shortlived species in desert environments (Wharton 1982, p. 149).

Seasonal incidence
Namadytes has primarily been collected during February through June, during the Southern Hemisphere late summer to early winter, as well as in October (Southern Hemisphere spring) (Table 1). N. cimbebasiensis, ranging from north-western South Africa to south-western Namibia (Fig. 6) occurs during March-May, while N. maculiventris, the species with the smallest geographic range restricted to southern Namibia (the type locality is on the South African bank of the Orange River, Fig. 6), occurs in February-March and October, and N. vansoni, the most abundantly collected species distributed throughout much of Namibia (Fig. 6), occurs in February-June and October. It is interesting to note that the October records represent the collecting events of the holotypes of N. pallidus (junior synonym of N. maculiventris) and N. prozeskyi (junior synonym of N. vansoni). Namadytes has not been sampled during the hottest months of the year, i.e., December-January, but has been collected in the cooler spring and late summer to early winter months. However, when one takes a closer look at the temperature and rainfall patterns at specific localities, taken from World Weather Online (http://www.worldweatheronline.com), a different picture emerges (see Table 2 for details). At Gobabeb, the hottest months are March-April (Suppl. material 4) and the wettest are February-April and June (Suppl. material 5) coinciding with the occurrence of N. vansoni. Further north at the northernmost distribution of this species around Khorixas, where it occurs in May, the average temperature is higher in May than in any other month between February-August (Suppl. materials 8,9). At the type locality of N. vansoni (Seeheim near Keetmanshoop), the holotype was collected during May, which is one of the coolest months during the year (Suppl. materials 6, 7). N. maculiventris occurs at Aus and Vioolsdrift during the hotter months of the year (February-March, Suppl. materials 2, 3, 14, 15) and during one of the median temperature months (October) near Keetmanshoop. N. cimbebasiensis occurs in March-April during a time of high temperature (see Suppl. materials 12, 13 for nearest Table 1. Seasonal incidence of Namadytes species. available weather station in Upington) and during a cooler month (May) at its type locality near Maltahöhe (Suppl. materials 10, 11). Despite not occurring during the peak of the summer, locally Namadytes does occur during the hottest months as well as cooler time sod the year. These data provide a glimpse at the temperature tolerance within species as, for example, N. maculiventris occurs at Vioolsdrift with an average high temperature of 19°C (March) and near Keetmanshoop with an average high temperature of 32 °C (October).

Biodiversity hotspots
The biodiversity hotspots sensu Conservation International (Myers et al. 2000) are areas of high plant endemism in which the habitat has been destroyed to a considerable extant and which are under threat of more destruction. Evaluating the presence/absence of Diptera species in these priority areas earmarked for conservation can determine whether these species will also be preserved when funding is made available for their protection (e.g., ). In a number of recent taxonomic revisions on Mydidae (Dikow 2010, Dikow 2012, it was discovered that several species within the studied genera are endemic to a particular hotspot, occur within a hotspot (but are not endemic to it), or occur only outside of these hotspots. Of the three species dealt with in this contribution, none occur or Table 2.
Namadytes species and the temperature and occurrence at selected localities. Temperature data from WorldWeatherOnline. Note that selected localities are places for which temperature data are available, for example, N. cimbebasiensis has not been collected at Upington, but north, north-east, and north-west of it.
are endemic to any biodiversity hotspot sensu Conservation International (see Fig. 6). Therefore, species of Namadytes would not benefit when only the biodiversity hotspots will receive funding for conservation and future habitat destruction and lack of conservation initiatives might have an effect on local populations.