Moegistorhynchus Macquart, 1840

Barraclough, David A. & Colville, Jonathan F., 2024, Revision of the endemic South African genus Moegistorhynchus Macquart (Diptera: Nemestrinidae), with a species key, description of three new species and comments on pollination biology and biogeography, Zootaxa 5519 (1), pp. 1-37 : 4-6

Genus Moegistorhynchus Macquart, 1840

Moegistorhynchus Macquart, 1840: 12 [ 1841: 290]. Type species: Nemestrina longirostris Wiedemann, 1819 , by designation of Bequaert (1935: 491).

Diagnosis relative to the Afrotropical genera

Head with face not prominent in profile, not projecting forwards or snout-like. Postpedicel well developed and separate from the slender and elongate style which nearly always has two short basal segments. Ocelli well developed and present in both sexes. Proboscis not vestigial, well developed and always obvious in profile, sometimes very much longer than body length. Wing not strongly tapered apically and hind margin not sinuous in appearance; all apical veins terminating anterior to wing apex; extensive apical reticulation in radial and medial sectors (cells divided by numerous auxiliary crossveins) in apical third of wing distal to diagonal crossvein; cell M 4 divided by at least one crossvein. Male postabdomen: hypandrium well developed and separate from the gonocoxite, gonostylus and inner gonocoxal process, which are all free structures; phallus free. Female postabdomen: ovipositor telescopeshaped with many retractile segments; cerci short and not sabre-like; two spermathecae.

Compared with the other two southern African genera of Nemestrininae, Moegistorhynchus is immediately distinguished by the well-developed reticulate wing venation in all species.

Relationship between Moegistorhynchus and other genera

All significant revisionary studies of the Nemestrinidae (e.g., Bequaert 1935; Bernardi 1973) have considered Moegistorhynchus (a likely monophyletic group) to be most closely related to the widespread and speciose Palaearctic genus Nemestrinus . Indeed, many species of Nemestrinus have reticulate wing venation, as in Moegistorhynchus . Richter (1997) recorded 66 species of Nemestrinus , almost all of them from the Palaearctic Region (see, also, El-Hashash et al. 2021). We have not reviewed the world fauna and cannot comment further on the relationship with Nemestrinus . However, it should be noted that Bernardi (1973) suggested that the exceptionally elongate and slender claws and long pulvilli and empodium define Moegistorhynchus . He also stated that Moegistorhynchus species had a ventral “tuft of hairs”, presumably on the male hypandrium. We can confirm that this tuft of pile may be obvious in some species, such as in M. braunsi (our Fig. 9.2 ), but it appears to be greatly reduced or absent in other species of the genus. This suggests that it has little value in defining Moegistorhynchus . Theron et al. (2023), using molecular data, considered Moegistorhynchus to be a monophyletic group and the sister group to Prosoeca Schiner (inclusive of Stenobasipteron ).

Review of important taxonomic characters

The southern African Nemestrinidae are a taxonomically difficult group and the genus Moegistorhynchus is no exception. Many of its species are large and morphologically dramatic, but some of the important taxonomic characters—especially those relating to wing patterning, colour and distribution of pruinescence and pile and general ground colour—are somewhat intangible and very difficult to describe in words or to accurately feature in digital imagery. A high-quality stereomicroscope and expert use of focused incident and background lighting are required to accurately reveal important character states. Some of the more important taxonomic characters are discussed below (characters are numbered per body part):

Antenna: (1) colour of the postpedicel; (2) development of the basal annulation on the postpedicel; and (3) the number of short basal segments on the style. The ground colour of the antenna may be influenced by the age of the specimen and greasiness. The appearance of the basal annulation is determined by the proper use of incident lighting as well as greasiness. It is sometimes very difficult to distinguish the two basal segments of the style and very focused and intense incident lighting is required; the two segments may appear to be partially fused.

Proboscis: (1) overall length and (2) relative length. Proboscis length has long been an important character in nemestrinid taxonomy. In Moegistorhynchus , it is probably the most important character and helps separate species pairs (see species key below), such as M. longirostris and M. brevirostris . It is also useful to compare proboscis length relative to body length. Note, however, that there can be dramatic intraspecific variation in proboscis length; this has long been noted for M. longirostris , for example.

Wing: (1) patterning and colour/infuscation and (2) crossvein development in cell CuP. The colour of the patterning on the wing may vary intraspecifically across the range of a species and may be influenced by the age of the specimen (fresh specimens always have darker and more obvious patterning). It is very important to examine the wing with an appropriate combination of backlighting and incident lighting, which always reveals the transparent/ hyaline sections of the wing membrane. The lack of clear-cut transparent/hyaline sections of wing membrane is an important character state and helps with defining species. Parts of the wing tend to have more or fewer transparent/ hyaline areas. Moegistorhynchus , rather unexpectedly, has very few other venational characters of any taxonomic value. However, the relative development of crossveins in cell CuP is of some importance and may separate species (see species key below).

Postalar callus: (1) development of a sharply pointed cuticular projection near its middle. This remarkable character state is a likely autapomorphy of M. manningi sp. nov.

Abdominal dorsum: (1) colour of pruinescence and pile; (2) development and clustering of pile at posterolateral corners of T 3– T 5; (3) general distribution and length of pile over tergites; and (4) ground colour. The colour and distribution of the pruinescence on T 2 is an important character and helps distinguish groups of species in Moegistorhynchus . Appropriate use of lighting is crucial; in older specimens the silver pruinescence may be less obvious or even hard to discern and age and greasiness can obscure it. The development and clustering of pile at the posterolateral corners of T 3– T 5 is another important character and, for example, strong clustering of elongate black pile is one of the defining character states of M. longirostris (males, especially). The distribution and length of pile over much of the tergites is also important and may vary intraspecifically. The apparent ground colour is influenced by the development of pruinescence and the distribution of pile, being important for distinguishing species.

Male terminalia: (1) epandrium development and (2) gonostylus shape apically. The shape and development of the epandrium is the most important character of the terminalia and may distinguish species. It is typically visible in situ and is therefore potentially useful in the field. Note that there may be some instraspecific variation in the shape of the epandrium. The shape of the apical part of the gonostylus is of minor value and helps distinguish two species.

General comments: Although the spermathecae were examined for most of the species of Moegistorhynchus they did not seem to offer important or useful taxonomic characters and were not studied further.

Key to the species of Moegistorhynchus Macquart

1. Wing with paler areas all a distinctive opaque creamy white and not transparent or hyaline ( Fig. 5.7 ). Postalar callus with a small sharply pointed cuticular projection near its middle ( Fig. 5.10 ). Style of antennal flagellum with one relatively short basal segment ( Fig. 5.4 )..................................................................... M. manningi sp. nov.

- Wing with clear-cut transparent or hyaline markings, such areas never all an opaque creamy white (one or two small, isolated creamy white marks sometimes present) (see e.g. Fig. 4.7 ). Postalar callus smooth over entire surface, without a small sharply pointed cuticular projection. Style of flagellum with two short basal segments (e.g. Fig. 8.4 ), although these sometimes may appear fused......................................................................................... 2

2. First abdominal tergite with distinct silver pruinescence along part of anterior margin; second abdominal tergite with silver pruinescence restricted to lateral areas and with medial section appearing variably dark to the naked eye (e.g. Fig. 4.9 ). Postpedicel typically with a paler (yellow-brown to orange) basal annulation (e.g. Fig. 4.4 ), this particularly noticeable on inner surface.............................................................................................. 3

- First abdominal tergite without obvious silver pruinescence anteriorly; second abdominal tergite almost entirely silvery pruinescent (e.g. Fig. 8.8 ). Postpedicel typically without a paler (yellow-brown to orange) basal annulation (e.g. Fig. 8.4 ); if this seemingly apparent then no distinct boundary line between pale and dark ground colour on inner surface............ 4

3. Proboscis strikingly elongate, 2.0–5.5 x body length. Abdomen (especially in male) with striking dense clusters of backwardly directed (usually) dark pile on posterolateral corners of third to fifth tergites ( Fig. 4.8 ).... M. longirostris ( Wiedemann, 1819)

- Proboscis short, length less than body length. Abdomen (especially in male) without obvious dense clustering of backwardly directed dark pile on posterolateral corners of third to fifth tergites (this instead resembling serial black pile) ( Fig. 3.8 ).............................................................................. M. brevirostris ( Wiedemann, 1821)

4. Proboscis short, at most slightly (up to 1.3 x) longer than body length............................................ 5

- Proboscis strikingly elongate, typically more than twice body length............................................. 6

5. Abdominal dorsum noticeably hirsute, with pile on T3 and T4 reaching length of T4 lateral margin and present over much of surface ( Fig. 7.8 ); ground colour medium brown. CuP with single complete crossvein reaching hind margin ( Fig. 7.7 )............................................................................................ M. strillii sp. nov.

- Abdominal dorsum not noticeably hirsute, with short and sparse pile on T3 and T4 which is much shorter than length of T4 lateral margin and is mainly restricted to marginal areas ( Fig. 8.8 ); ground colour typically dark brown to black. CuP with 1 (occasionally 2–3) short and incomplete crossveins, these not reaching hind margin ( Fig. 8.7 )........... M. turneri sp. nov.

6. Postpedicel entirely pale. Posterolateral sections of abdominal T3 and T4 with pale pile. Epandrium not divided into two obvious lobes dorsally and with very small apico-medial notch only ( Fig. 9.1 ). Gonostylus broadly rounded apically...................................................................................... M. braunsi Bequaert, 1935

- Postpedicel typically mostly dark. 1 Posterolateral sections of abdominal T3 and T4 typically with relatively dense fringe of dark pile, especially in male. Epandrium prominently divided into two obvious lobes dorsally and with broad and extensive medial notch ( Fig. 10.1 ). Gonostylus sharply pointed apically.................................. M. perplexus Bequaert, 1935

Figures

FIGURE 3 (3.1–3.4). Moegistorhynchus brevirostris (Wiedemann, 1821) (lectotype male). 1. Whole body, lateral view. 2. Label data. 3–4. Head. 3. Frontal view. 4. Oblique lateral view, showing detail of antennae.

FIGURE 4 (4.1–4.4). Moegistorhynchus longirostris (Wiedemann, 1821) (male). 1. Whole body, lateral view. 2. Label data. 3–4. Head. 3. Frontal view. 4. Oblique lateral view, showing detail of antennae with orange basal annulation of postpedicel arrowed.

FIGURE 5 (5.1–5.4). Moegistorhynchus manningi sp. nov. (male holotype). 1. Whole body, lateral view. 2. Label data. 3– 4. Head. 3. Frontal view. 4. Oblique lateral view, showing detail of antennae with style with only one short basal segment (arrowed).

FIGURE 7 (7.1–7.4). Moegistorhynchus strillii sp. nov. (male holotype). 1. Whole body, lateral view. 2. Label data. 3–4. Head. 3. Frontal view. 4. Oblique lateral view, showing detail of antennae.

FIGURE 8 (8.1–8.4). Moegistorhynchus turneri sp. nov. (male holotype). 1. Whole body, lateral view. 2. Label data. 3–4. Head. 3. Frontal view. 4. Oblique lateral view, showing detail of antennae: style of flagellum with two short basal segments (arrowed).

FIGURE 9 (9.1–9.6). Male terminalia: dorsal (left) and ventral (right) views. 1–2. Moegistorhynchus braunsi (annotated). Abbreviations: cerc—cercus; epand—epandrium; goncx—gonocoxite; gonst—gonostylus; hypd—hypandrium; ph—phallus. Note elongate tuft of pile on hypd. 3–4. Moegistorhynchus brevirostris. 5–6. Moegistorhynchus longirostris.

FIGURE 10 (10.1–10.4). Male terminalia: dorsal (left) and ventral (right) views. 1–2. Moegistorhynchus perplexus. 3–4. Moegistorhynchus turneri.