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

Dr Torsten Dikow; Ms Stephanie Leon

doi:10.3897/BDJ.2.e1071

. 2014 Mar 10;(2):e1071. doi: 10.3897/BDJ.2.e1071

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

Torsten Dikow ^†,^✉, Stephanie Leon ^‡

PMCID: PMC4031440 PMID: 24891827

Abstract 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.

Keywords: Diptera , Mydidae , Syllegomydinae , Namadytes , Afrotropical Region, taxonomy

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., Namadytes prozeskyi and Namadytes vansoni, were known from females only, while Namadytes maculiventris and Namadytes pallidus were known only from males, and Namadytes 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 (CH₃COOH) and rinsing in distilled water (H₂O). They are temporarily stored in 75% ethanol (C₂H₅OH) for examination and illustration and eventually sealed in polyethylene vials containing 100% glycerine (C₃H₈O₃) 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: yyyy-mm-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). The occurrence of all species is illustrated in distribution maps plotted with SimpleMappr (Shorthouse 2010) with all of those localities for which co-ordinates are available. Type localities are plotted with a square symbol while all other specimens are plotted with a circular symbol. The distribution map includes Biodiversity Hotspots sensu Conservation International and the electronic shape-files were obtained from: http://www.conservation.org/where/priority_areas/hotspots/Pages/hotspots_main.aspx. The specimen occurrence data are deposited as a Darwin Core Archive (DwC-A) in the Global Biodiversity Information Facility (GBIF). The dichotomous, interactive key has been build with Lucid Phoenix and the multi-access, matrix-based key with Lucid Builder and both have been deposited in the IdentifyLife archive, registered in Lucidcentral, and made available on the senior author's research web-site. All taxon names have been registered in ZooBank (Pyle and Michel 2008).

Institutions providing specimens

Institutions providing specimens are listed below, together with the abbreviations used in the text when citing depositories (institutionCode), a link to the record in the Global Registry of Biodiversity Repositories (GRBio), and the people who kindly assisted: AMGS – Albany Museum, Grahamstown, Eastern Cape, South Africa (A. Kirk-Spriggs, S. Gess); BMNH – The Natural History Museum, London, UK (E. McAlister); CSCA – California State Collection of Arthropods, Sacramento, California, USA (M. Hauser); INHS – Illinois Natural History Survey, Urbana-Champaign, Illinois, USA (D. Webb, M. Irwin); NMNW – National Museum of Namibia, Windhoek, Khomas, Namibia (A. Kirk-Spriggs); NMSA – KwaZulu-Natal Museum, Pietermaritzburg, KwaZulu-Natal, South Africa (B. Muller); SAMC – Iziko South African Museum, Cape Town, Western Cape, South Africa (M. Cochrane); SANC – South African National Collection of Insects, Pretoria, Gauteng, South Africa (R. Urban); TMSA – Ditsong National Museum of Natural History (formerly Transvaal Museum), Pretoria, Gauteng, South Africa (M. Krüger); USNM – National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.

Data resources

DRYAD: natural-language species descriptions from Lucid Builder in SDD format (also available as Suppl. material 1).
GBIF: specimen occurrence data – 5e6acf4c-e913-45fd-8466-5c0b92c322dd.
Morphbank:: Biological Imaging: high-resolution photographs – 835218.
SimpleMappr: distribution map – 2368 (as in figure 1) and in Google Earth as a KML file.
Lucid Builder: illustrated, multi-entry, matrix-based identification key – asilodflies.si.edu and IdentifyLife.
Lucid Phoenix: illustrated, dichotomous identification key – asilodflies.si.edu.

Taxon treatments

Namadytes

Hesse, 1969

urn:lsid:zoobank.org:act:528203A4-E5FB-46E5-A5DF-811EDE021F18

Namadytes Hesse, 1969: 278.
Namamydas Hesse, 1969: 284 junior synonym sensuHesse 1972: 139 (ZooBank LSID).
Namadytes Namadytes vansoni Hesse, 1969 – Hesse 1969: 278. ; Bowden 1980: 331. catalog

Description

Female genitalia (Fig. 1): densely arranged anteriorly directed setae present on T7–8 and S7–8; T8 with broad anterior rectangular apodeme; T9 formed by wide, rectangular sclerite with median protuberance; T9+10 entirely fused, T10 divided into 2 heavily sclerotized acanthophorite plates, 8–10 acanthophorite spines per plate; 2 spermathecae, all equally large, formed by ± expanded heavily sclerotized ducts; individual spermathecal duct short; S9 (furca) formed by 1 sclerite, ring–like (joined anteriorly and posteriorly), anterior furcal apodeme present, 2 lateral projections forming divided apodeme, lateral furcal apodeme present, median furcal bridge absent.

Figure 1. — *Namadytes* *cimbebasiensis* ♀ terminalia (NMNW-H7809), dorsal view showing position of internal furca and spermathecae. Scale line = 1 mm.

Male terminalia (e.g., Fig. 2) T1–7 well-developed, entirely sclerotized, T8 postero-medially weakly sclerotized, with anterior transverse sclerotized bridge connecting lateral sclerites; T7–8 anteriorly with 2 lateral apodemes; S6 regular, without any special setation postero-medially, S8 simple plate, entire (undivided) ventro-medially, not fused to T8 dorso-laterally; epandrium formed by single sclerite (fused medially ± entirely), distally in dorsal view blunt, evenly rounded; subepandrial sclerite without lateral or median protuberances; hypandrium strongly concave, cup-shaped, entirely sclerotized ventrally (forming a single sclerite), entirely fused with gonocoxite, forming a gonocoxite-hypandrial complex, supra-hypandrial sclerite absent; gonocoxite dorso-ventrally flattened in distal ½, higher in proximal ½, without median or lateral protuberance, gonocoxal apodeme absent; 2 functional aedeagal prongs, short and wide, medio-distally connected; aedeagal epimere absent; lateral ejaculatory process present, large cylindrical sclerite; ejaculatory apodeme formed by single dorso-ventrally oriented plate; ventro-median margin of dorsal aedeagal sheath heavily sclerotized (appearing entirely closed); dorsal aedeagal sheath long, sperm sac entirely covered; sperm sac appearing ± heavily sclerotized.

Figure 2a. — *Namadytes* *cimbebasiensis* ♂ terminalia (NMNW-H7808). Scale lines = 1 mm.

Figure 2b. — *Namadytes* *cimbebasiensis* ♂ terminalia (NMNW-H7808). Scale lines = 1 mm.

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.

Figure 3. — *Namadytes* *vansoni* male (AAM-002988). Scale line = 2 mm.

Distribution

Namadytes is distributed in southern Africa and restricted to Namibia and north-westernmost South Africa (Fig. 4).

Figure 4. — Distribution of *Namadytes*.

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 antero-median V-shaped indentation on the antepronotum and the presence of white setae on 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.