Moegistorhynchus strillii Barraclough & Colville, 2024

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 : 24-26

Moegistorhynchus strillii Barraclough & Colville sp. nov.

( Figs 7.1–7.9 , 12 )

Type locality. Groot Winterhoek mountains north of Tulbagh , Western Cape province .

Type material ( in SAMC): South Africa: Western Cape: HOLOTYPE: ♂: “ Gt. Wint-hoek / Tulbagh / 4,500 ft. / [on reverse side of label] Nov. 1916 / Lightfoot”; “Megistorhynchus / brevirostris / ♂ Wied.”; “ Moegistorhynchus / sp. Not brevi- / rostris (Wied) / [on reverse of label] det / F.W. Gess. ”; “This is probably not / M. brevirostris Wied / s.str., but separate / species. M. brevirostris / probably another atypical / var. of longirostris / with very short proboscis / A.J. Hesse ”. The holotype is in fairly good condition, although the right wing apex is tattered.

Etymology. The species name strillii refers to Mrs Strilli Oppenheimer and honours the financial support offered by the Oppenheimer family which made possible the publication of this paper and the description of this species.

Diagnosis. Style with two basal segments. Proboscis short, slightly longer than body length. Postalar callus smooth over entire surface. Wing with clear-cut transparent or hyaline markings, such areas never an opaque creamy white; CuP with single complete crossvein reaching to hind margin. Ground colour of abdominal dorsum medium brown. Second abdominal tergite almost entirely densely silver pruinescent across its width; pile on T3 and T4 elongate, reaching length of T4 lateral margin, and present over much of surface.

Description. Body length 9.34 mm ( Fig. 7.1 ); wing length 11.51 mm; proboscis length 8.87 mm. Head ( Figs 7.3–7.4 ): colouring medium to dark brown, except scape and pedicel mostly yellow. Postpedicel mostly dark brown, but with hint of orange ground colouring on inner basal surface. Male with anterior ocellus and posterior ocelli separated by deep transverse groove; anterior and posterior ocelli all about equidistant apart and therefore forming the three corners of an equilateral triangle. Frons with elongate pile, a mixture of creamy and black pile (but mostly pale); pile largely absent medially, here only present anteriorly where it is recumbent. Style of flagellum with two short basal segments, with second segment reaching 1.5 x length of first segment. Proboscis short, length only slightly longer than body length. Thorax ( Figs 7.5–7.6 ): scutum medium to very dark brown, although yellow-brown on postalar calli and adjacent to wing insertion and on disc of scutellum, and also irregularly paler posteriorly beneath silver pruinescence just anterior to scuto-scutellar suture. Paired median silver pruinescent vittae (pruinescence somewhat faint) extend uninterrupted from anterior margin to scuto-scutellar suture. Scutellum densely silver pruinescent anterolaterally and less so along posterior margin just posterior to disc. Pile on scutum a mixture of yellow (predominant) and black, short but profuse; largely sparse to absent on posterior half (although present here on postalar calli and disc of scutellum and otherwise as sparse elongate dark hairs). Postalar callus smooth over entire surface. Legs: almost entirely yellow. Fore femur with elongate backwardly directed pale pile which is intermixed with a few black hairs, this pile sometimes reaching almost half femur length. Mid and hind femora with sparse ventral pile (a mixture of dark and pale) along entire length of mid femur and along basal two-thirds of hind femur. Wing ( Fig. 7.7 ): very slender, length at least 3.5 x maximum width. Infuscation an indistinct pale brown. Patterning therefore rather irregular and distributed over much of wing, as in figure; hyaline areas not strikingly distinguished or delineated and merge into smoky brown colouring. CuP with complete crossvein extending entire distance to wing margin (with hint of mid-length appendix on one wing). Abdomen ( Figs 7.8–7.9 ): relatively compact and slender, width slightly broader than maximum width of thorax. Ground colour medium brown, but may be partly yellow on several sternites. T1 entirely brown and silver pruinescence completely lacking; pile dense and short, mostly yellow to cream or white. T2 densely silver pruinescent across entire width (except posteromedially, although this may be membrane); pile largely absent. T3 largely medium brown, but with striking paired medial silver pruinescent markings (elongate-ovoid and transversely positioned) on anterior half and silver pruinescent on lateral margins; silver pruinescent along most of posterior margin; pile profuse and very elongate, this pale anteriorly but with more dark pile posteriorly, pile longest anteriorly, length almost reaching length of T3 lateral margins, largely absent over silver pruinescent elongate-ovoid areas. T4 similarly coloured and patterned, but silver pruinescent posterior margin more extensive, with this pruinescence merging broadly with lateral margins; pile typically sparse anteriorly, but then more profuse laterally and posteriorly, this dark in colour, longest hairs reaching length of T4 lateral margin. T5 even more extensively silver pruinescent, with small brown area medially and submedially (the latter very small); pile dense and elongate, laterally only, length here the same as on T4. T6 was part of the dissection of the male postabdomen and cannot be described. Sternites yellow-brown to medium brown with silver pruinescence; pile notably elongate and white on S3. Male postabdomen: epandrium moderately robust in dorsal view, maximum width somewhat broader than length with small apical notch above cerci, apicolateral extremities very broadly rounded in lateral view, somewhat flattened apically. Gonostylus with no obvious vestiture along inner medial margin, apical region narrowed and very slightly inwardly curved, sharply pointed at extreme apex. Inner gonocoxal process not sharply pointed apically, here rather broadly rounded, narrowed at mid-length. Phallus apex coincident with gonostylus apices in ventral view, bluntly tapered apically, without dentate subapical margins.

Relationships and distribution ( Fig. 12 ). Moegistorhynchus strillii is most similar to M. turneri sp. nov., although it is rapidly distinguished by having the abdominal dorsum with a paler (medium brown) ground colour and strikingly elongate pile. Vegetation type: Winterhoek Sandstone Fynbos (FFs5).

Discussion. This species is known only from the holotype, which was collected 108 years ago in the Groot Winterhoek mountains north of Tulbagh at an altitude of about 1370 metres. It is a highly distinctive species and may be extinct. We say this because the Groot Winterhoek mountains are relatively well collected; in fact two other species of Moegistorhynchus have been collected there. However, no material besides the male holotype has ever been collected. Over the years (see label data cited above) the species was misidentified as M. brevirostris and as a ‘variety’ of M. longirostris . Bezzi (1924: 189), for example, considered this species to be M. brevirostris . However, it is clearly neither of these two species given that the second abdominal tergite is almost entirely silver pruinescent.

The male postabdomen of the holotype had been dissected from the abdomen several decades ago and is stored in a glycerine-filled microvial with the specimen. Although it was possible to describe the postabdomen (see above), its condition was so poor and unstable at the type of imaging that we decided not to image it given the risk of further substantial damage.

Figures

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 12. Distribution of the seven species of Moegistorhynchus across the coastal and montane areas of the Fynbos and Succulent Karoo Biomes (includes confirmed iNaturalist records to February 2024).