Centrioncus bururiensis, Feijen & Feijen, 2023

Feijen, Hans R. & Feijen, Cobi, 2023, A revision of Centrioncus Speiser (Diptera, Diopsidae, Centrioncinae) with descriptions of new species from Angola, Burundi, and Kenya, ZooKeys 1144, pp. 1-93 : 1

Centrioncus bururiensis sp. nov.

Figs 2 , 29 , 33-36 , 37-40 , 41-43 , 44-49 , 50-54

Type material.

Burundi, holotype, ♀, Bururi Nat. Forest, 3°55'49"S, 29°37'1"E, 1955 m, 7-21.ix.2010, R. Copeland, malaise trap, indigenous forest near stream (NMKE). Paratypes: 1 ♀, 1 ♂, same data as holotype (ICIPE, RMNH).

Diagnosis.

Centrioncus bururiensis sp. nov. can be recognised by the mesally slightly depressed, uniformly pruinose frons; mainly glossy collar; pruinose blackish brown scutum; pruinose, blackish brown scutellum with brown spines; pleura blackish brown with ventral edge of proepimeron, dorsal third of anepisternum, posterior quarter of anepimeron, and greater ampulla brown; scutellar spine/scutellum ratio: 0.8-0.9; apical seta/scutellar spine ratio: 0.94-1.18; pale brown, strongly incrassate fore femur 1 (l/w ratio: 2.63-2.93) with ~ 38.5 tubercles, dark apical third on mesal side; small central brownish wing spot around crossvein r-m in distal tip of cell br and basal quarter of cell r4+5, somewhat extending into cell bm+dm (Fig. 2 ); tergites blackish brown, thinly pruinose; sternites 4 and 5 rectangular with each a pair of small, heavily sclerotised areas basally; sternite 6 short, almost as broad as segment, laterally tapering; female 7th spiracle in membrane; anterior sclerite of female sternite 7 rectangular, w/l ratio: ~ 2.6 (Figs 42 , 43 ); posterior sclerite of female sternite 7 broad, strongly curved, U-shaped, well sclerotised (Figs 42 , 43 ), posterolateral apices tapering; elongate female cercus with l/w ratio: ~ 4.5; subanal plate pentagonal, laterally rounded and apically tapering into short extension; spermathecae heavily sclerotised, smooth, flattened (Fig. 49 ), rounded in cross section, with small apical dimple; outer and median arms of surstylus broadly joined, with short broad common base (Fig. 51 ); outer arm triangular, apically 4 tubercles; median arm very broad, parallel-sided, apically 11 stout, spinous setae; inner arm half the length of median arm, with apophysis; subepandrial clasper (Fig. 53 ) with long strong basal constriction, extended towards meson, rectangular with apical corners square, mesal basal corner rounded; male cercus (Fig. 54 ) slender, distinctly broadening in apical third but without distal lateral extension.

Description.

Measurements. Body length ♀ 5.8, 5.8 mm, ♂ 4.6 mm, width of head ♀ 1.28, 1.27 mm, ♂ 1.07 mm, wing length ♀ 5.3, 5.2 mm, ♂ 4.1 mm, length of scutellar spine ♀ 0.39, 0.36 mm, ♂ 0.27 mm.

Head. Frons slightly depressed mesally (Fig. 34 ), dark brown but anterolateral margins pale brown, uniformly thinly pruinose; posterior side of head dark brown with paler brown ventral margin (Fig. 36 ), pruinose especially posterior to ocellar tubercle and near eye margins; face yellowish brown, thinly pruinose but densely pruinose along eye margins (Figs 34 , 35 ); antenna yellowish brown but dorsal edge of funiculus darker (Figs 34-36 , 38 ); maxillary palpus dark (Figs 34 , 35 ); outer vertical seta in ♀ 0.41 mm and in ♂ 0.31 mm, fronto-orbital setae in ♀ 0.29 mm and in ♂ 0.18 mm (Figs 34 , 36 ).

Thorax. Collar glossy dark brown, posterior and lateral edges pruinose; scutum blackish brown and pruinose (Figs 33 , 36 ), tiny pale spot around base of intra-alar seta, humeral callus brown and less pruinose; scutellum dark brown, pruinose, scutellar spines brown (Figs 33 , 36 ); pleura blackish brown with ventral edge of proepimeron, dorsal third of anepisternum, posterior quarter of anepimeron, and greater ampulla brown (Fig. 36 ), but, like in all Centrioncus , paler sections can also turn dark (Fig. 33 ); pleura mainly pruinose, glossy sections include ventral edge of anepisternum and anterior spot on katepisternum (Fig. 36 ); posterior notopleural seta, supra-alar and infra-alar setae present, infra-alar seta longest, followed by posterior notopleural seta, supra-alar seta on inconspicuous carina; basiliform prosternum lanceolate and sharply pointed anteriorly (Fig. 35 ); scutal length/scutal width ratio: 1.0 in ♀ and ♂; scutellum sticking up at an angle of just over 20° from body axis; scutellar spines almost aligned with dorsal plane of scutellum (Fig. 36 ), diverging at angle of ~ 50°; scutellar spine/scutellum ratio: 0.9 in ♀, 0.8 in ♂; scutellar spine/length of body ratio: 0.06-0.07 in ♀, 0.06 in ♂; apical seta/scutellar spine ratio: 0.94 in ♀, 1.18 in ♂, scutellar length/scutellar width (at base) ratio: ~ 0.70.

Wing. Almost transparent but slightly tinged; small, central brownish spot around crossvein r-m in distal tip of cell br and basal quarter of cell r4+5, vaguely extending into cell bm+dm (Fig. 2 ); some vague infuscation around vein M4 proximally of crossvein dm-m; glabrous basal areas only include cells bc and c and basal third of cell br; crossvein h distinct; cell sc almost closed; vein CuA+CuP from vein CuP onward extending under angle of 30° to wing margin in almost straight line (Fig. 2 ); vein M4 continuing distal of crossvein dm-m very slightly turning downwards towards wing margin; cell cua triangular; alula distinct; crossvein bm-m hardly indicated.

Legs. Coxa 1 and trochanter 1 whitish, thinly pruinose (Figs 35 , 36 ); femur 1 glossy, yellowish brown with dark brown spot on apical third of inner side, darker in ♂ and extending to outer side (Figs 33 , 36 , 39 ); tibia 1 dark brown, pruinose; metatarsus 1 yellowish, other tarsal segments whitish; mid and hind legs pale yellowish; femur 2 with pale brownish apex; outer apical quarter of femur 3 with brown spot (Fig. 37 ); femur 1 strongly incrassate in ♀ and ♂ (Figs 33 , 36 , 39 , 40 ), l/w ratio in ♀: 2.87, 2.93 and in ♂: 2.63, inner rows of spinous setae (Figs 39 , 40 ) with 4.8 setae (n = 6, range 4-5), outer rows with 4.0 setae (n = 6, range 3-5), inner rows of tubercles with 18.3 tubercles (n = 6, range 17-20), outer rows with 20.2 tubercles (n = 6, range 18-23); femur 3 (Fig. 37 ) with 6.8 distal tubercles (n = 4, range 5-8); setal formula 4.0, 4.8, 20.2, 18.3, 6.8; no apical spurs on femora 2 and 3.

Preabdomen. Tergites blackish brown, very thinly pruinose; sternites 1-5 yellowish brown, sternites 1-3 glossy and clothed with some setulae (Fig. 41 ), sternites 4-5 thinly pruinose, with some setulae; sternite 1 very short, constricted medially; sternite 2 anteriorly with small more sclerotised sclerite (plesiomorphic equivalent of intersternite 1-2 found in most Diopsidae ), laterally thinly connected to main sternite, separated from main sclerite by short, non-sclerotised “gap” (Fig. 41 ); sternites 2-5 rectangular, slender, more or less equal in width (Fig. 41 ), sternite 3 20% shorter than sternite 2, sternite 4 only half length of sternite 2 and sternite 5 only one-third length of sternite 2; sternites 4 and 5 both with pair of small, heavily sclerotised sections anteriorly (Fig. 41 ); sternite 6 short and broad, laterally tapering, almost as broad as segment, 1.6 × as wide as sternites 1-5 (Fig. 42 ).

Female postabdomen. Tergite 7 (Figs 42 , 44 ) brown, with large mesal gap posteriorly, lateral edges hardly curved under ventrally; suture in basal ring of segment 7 hardly visible; 7th spiracle in membrane (Fig. 43 ); anterior sclerite of sternite 7 rectangular, slightly tapering posteriorly (Figs 42 , 43 ), w/l ratio: ~ 2.6 (Table 8 ), glossy brown, with ~ 16 setulae and some microtrichia only on posterior edge; posterior sclerite of sternite 7 broad, strongly curved U-shaped (Figs 42 , 43 ), almost forming semicircle, posterolateral apices tapering, well sclerotised, clothed in microtrichia and with one apical setula; tergite 8 consisting of two oblong plates, well separated on meson (Fig. 45 ); sternite 8 consisting of two oblong plates; tergite 10 (Fig. 45 ) somewhat onion-shaped, extending posteriorly between cerci, clothed in microtrichia and a few setulae; cercus elongate, somewhat tapering posteriorly (Fig. 44 ; cut off in paratype, Fig. 45 ), l/w ratio: ~ 4.5; subanal plate (Fig. 46 ) somewhat pentagonal, laterally rounded and apically tapering into short extension, clothed in microtrichia except anterior edge, with ~ 12 setulae especially along posterior edge; spermathecae heavily sclerotised, smooth, flattened (Fig. 49 ), round in cross section, with small apical dimple; junction of ducts of paired spermathecae V-shaped (Fig. 49 ).

Male postabdomen. Tergite 6, sternite 8 and epandrium more brownish than blackish brown tergites 1-5; sternite 6 rectangular, almost as broad as tergite 6; epandrium broad and rounded (Fig. 50 ) with w/l ratio: 1.31, dark brown but paler brown along inner edges, clothed in microtrichia and with ~ 6 small setulae; surstylus in outer view (Fig. 50 ) not deeply bifurcated, with central patch of microtrichia on outer side; outer and median arms broadly joined, with short broad common base (Fig. 51 ); outer arm almost triangular, tapering apically, not constricted at base, with four apical, closely joined tubercles, basally to centrally with seven setulae on inner side and a few small setulae along posterior edge; median arm very broad, parallel-sided, with apically 11 stout, dark, spinous setae, some small pale setulae and two long setulae (Figs 50 , 51 ); inner arm linked to base of other arms, half-length of median arm, tapering apically, with one apophysis and five strong setulae; subepandrial clasper (Fig. 53 ) with long strong basal constriction, extended mesally, rectangular with apical corners almost square and mesal basal corner rounded, glabrous; cercus (Fig. 54 ) slender, distinctly broadening in apical third, without distal lateral extension, clothed in microtrichia, with short setulae mainly along mesal edge, length/greatest width ratio: 2.4 (Table 8 ); phallapodeme short; ejaculatory apodeme + sac (Fig. 52 ) very large, 10.4% of body length (Table 9 ), ejaculatory apodeme club-shaped, basally slender.

Egg. ♀ paratype contained 45 developing and developed eggs in abdomen. The eggs (Figs 47 , 48 ) measured ≤ 1.10 mm in length, with slightly elevated longitudinal ridges spanning from anterior pole to posterior pole with fine, nearly hexagonal microstructure between ridges (Fig. 48 ).

Distribution and habitat.

The new species is only known from the Bururi National Forest in Burundi. It was collected at an altitude of 1955 m. This small Afromontane Forest is relatively isolated from other similar forests. The type locality is shown on the map for Eastern Africa (Fig. 29 ).

Etymology.

The specific epithet of C. bururiensis sp. nov. refers to the place of origin for the holotype, the Bururi Forest in Burundi.

Remarks.

While cursorily examining the three flies of the Bururi Forest, the male fly appeared to be Centrioncus aberrans , given the apparently similar shapes of surstyli and cerci. However, the females with their clearly visible curved posterior sclerite of sternite 7 (Figs 42 , 43 ) did not belong to the C. aberrans species-group. This led to the initial assumption that this might be the first case of two Centrioncus species occurring sympatrically. However, closer examination of the male genitalia revealed distinct differences with those of C. aberrans . The female is also different from other described Centrioncus with the characteristic sternites 4, 5, and 7 and the spermathecae. The subanal plate of C. bururiensis sp. nov. is more like those of C. decoronotus and C. prodiopsis , not like C. aberrans (compare Fig. 46 vs. Feijen 1983: figs 49-51). The w/l ratio of the anterior female sternite 7 is like the ones for C. decellei , C. bytebieri and C. prodiopsis , certainly not like the one for C. aberrans (Table 8 ), while the shape of posterior sclerite of sternite 7 is more like the one for C. decoronotus and certainly not like C. prodiopsis or C. bytebieri (compare Figs 119 , 148 , 62 vs. De Meyer 2004: fig. 6).

It remains puzzling that the male genitalia of Centrioncus bururiensis sp. nov. indicates a possible relationship with C. aberrans , while the female genitalia contradicts such a relationship. Analyses, including molecular analysis, of a series of fresh material are required to resolve this issue. The number of 45 eggs found in a paratype was quite high. Feijen (1983) found in various Centrioncus and Teloglabrus species> 20 developing and developed eggs and stated that a fecundity of between 25 and 50 eggs seemed likely. The gravid female paratype was collected in September, coinciding with the start of the short rains in Burundi.

Figures

Figure 29. Distribution map of the seven Eastern African Centrioncus species.

Figures 1 - 4. Centrioncus, dorsal view of wings 1 ♂, C. aberrans, Timboroa Forest 2 ♀, paratype, C. bururiensis sp. nov., Bururi Nat. Forest 3 ♂ C. bytebieri, Ngangao Forest 4 ♀, paratype, C. copelandi sp. nov., Kasigau Mtn. Scale bars: 0.5 mm.

Figures 33 - 36. Centrioncus bururiensis sp. nov., Bururi Nat. Forest 33 ♂, paratype, habitus, dorsolateral view 34 - 36 ♀, paratype 34 head, anterolateral view 35 head, basiliform prosternum, ventral view 36 head, thorax, fore femora, lateral view. Scale bars: 0.5 mm.

Figures 37 - 40. Centrioncus bururiensis sp. nov., Bururi Nat. Forest 37, 39, 40 ♀, holotype 38 ♀ paratype 37 hind femur, outer view 38 antenna, lateral view 39 fore femur, inner view 40 fore femur, ventral view. Scale bars: 0.2 mm.

Figures 41 - 43. Centrioncus bururiensis sp. nov., Bururi Nat. Forest 41, 43 ♀, paratype 42 ♀, holotype 41 sternites 1 - 5, ventral view 42, 43 sternite 7, ventral view. Scale bars: 0.5 mm (41); 0.1 mm (42, 43).

Figures 44 - 49. Centrioncus bururiensis sp. nov., Bururi Nat. Forest 44 ♀, holotype 45 - 49, ♀, paratype 44 tergite 7, 8, 10, cerci, dorsal view (setulae not shown) 45 tergite 8, 10, basal cerci, dorsal view 46 subanal plate, ventral view 47 egg 48 egg, detail 49 spermathecae. Scale bars: 0.2 mm (44, 47); 0.1 mm (45, 46, 48, 49).

Figures 50 - 54. Centrioncus bururiensis sp. nov., ♂, paratype, Bururi Nat. Forest 50 epandrium, cerci, surstyli, posterior view 51 surstylus, inner view 52 ejaculatory apodeme + sac 53 subepandrial clasper, posterior view 54 cercus, posterior view. Scale bars: 0.1 mm.

Figures 118 - 121. Centrioncus decoronotus, ♀, Ol Doinyo Orok 118 sternites 1 - 5, ventral view 119 sternite 7, ventral view 120 spermathecae 121 egg, detail of external structure (L = line, R = ridge). Scale bars: 0.2 mm (118, 119); 0.05 mm (120, 121).

Figures 146 - 149. Centrioncus prodiopsis, ♀, Oloitokitok 146 sternites 1 - 6, ventral view 147, 148 sternite 7, ventral view 149 tergite 7 and cerci, posterolateral view. Scale bars: 0.5 mm (146); 0.1 mm (147 - 149).

Figures 61 - 67. Centrioncus bytebieri, ♀ 61 Ngangao Forest 62 - 67 Vuria Forest 61, 62 sternite 7, ventral view 63 subanal plate ventral view 64 spermathecae 65 sternites 8, 10, cerci, ventral view 66 egg 67 egg, detail. Scale bars: 0.2 mm (61, 62, 66); 0.1 mm (63 - 65, 67).