Centrioncus bytebieri De Meyer, 2004

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 bytebieri De Meyer

Figs 3 , 29 , 55-60 , 61-67 , 68-73

Centrioncus bytebieri De Meyer, 2004: 26; Karanja et al. 2014: 49.

Type material.

Kenya, holotype, ♂, Ngangao Forest, Taita Hills [3°21'38"S, 38°20'29"E, 1800 m], M. De Meyer (NMKE). Paratypes: 8 ♀ (1 ♀ as “allotype”), 7 ♂, same data as holotype; 8 ♀, 10 ♂, Chawia Forest, Taita Hills [3°28'56"S, 38°20'25"E]; 5 ♀, 6 ♂, Yale Forest, Taita Hills [3°24'7"S, 38°19'36"E]; 5 ♀, 2 ♂, Mbololo Forest, Taita Hills [3°19'36"S, 38°27'3"E]. All paratypes collected by M. De Meyer at altitudes of 1400-1800 m, allotype NMKE, 2 paratypes NHMUK, 2 paratypes NMSA, 46 paratypes MRAC.

Material studied.

Kenya: 2 ♀, Coastal Prov., Taita Hills, Mbololo Forest , malaise trap 3°20.00'S, 38°26.85'E, 1550 m, 29.iii-6.iv.1999 , Taita biodiversity project (ICIPE); 1 ♀, 1 ♂, Coastal Prov., Taita Hills, Fururu Forest , malaise trap, 3°25.78'S, 38°20.30'E, 1680 m, 23-29.i.1999 , Taita biodiversity project, (ICIPE); 1 ♀, Coastal Prov., Taita Hills, Chawia Forest , malaise trap next to small forest pond, 3.47908°S, 38.34162°E, 1614 m, 9-23.i.2012 , R. Copeland (ICIPE); 1 ♀, 4 ♂, Coastal Prov., Taita Hills, Vuria Forest , malaise trap, edge indigenous forest, 3.41428°S, 38.29178°E, 2162 m , 1 ♂ 12-6.vi.2011, 1 ♀ 11-25.i.2012, 1 ♂ 13-27.v.2012, 1 ♂ 25.vii-8.viii.2012, 1 ♂ 8-22.viii.2012, R. Copeland (ICIPE); 5 ♀, 1 ♂, Coastal Prov., Taita Hills, Ngangao Forest , malaise trap, indigenous forest, 3.36100°S, 38.34186°E, 1848 m , 1 ♀ 30.x-13.xi.2011, 2 ♀ 24.i-7.ii-2012, 1 ♀ 8-22.ii.2012, 1 ♂ 19.iv-3.v.2012, 1 ♀ 27.v-10.vi.2012, R. Copeland (ICIPE). In total 10 ♀ and 6 ♂ were studied.

Diagnosis.

Centrioncus bytebieri can be recognised by the pruinose frons with glossy spots; glossy collar; pruinose blackish brown scutum; scutellum blackish brown with brown lateral sides; scutellar spines brown; pleura blackish brown with largely brown proepisternum and strikingly brown central area formed by anepisternum, anepimeron and greater ampulla (Figs 55 , 57 ); scutellar spine/scutellum ratio: 0.95; apical seta/scutellar spine ratio: 1.14; pale brown, incrassate fore femur (l/w ratio: ~ 3.30) with ~ 33 tubercles, broad brown stripe on distal half; small, central brownish wing spot around crossvein r-m in distal tip of cell br and basal fifth of cell r4+5, somewhat extending into cell bm+dm (Figs 3 , 55 ); tergites blackish brown, syntergite with small pale spots in posterolateral corners (Fig. 60 ), tergite 3 with pale posterior band; sternite 4 trapezoidal; sternite 5 rectangular; sternite 6 short and broad; female 7th spiracle in tergite; anterior sclerite of female sternite 7 rectangular, w/l ratio: ~ 2.6 (Figs 61 , 62 ); posterior sclerite of female sternite 7 somewhat U-shaped, with posterolateral extensions almost extending to posterior corners of tergite 7, lateral sections outwardly curved (Figs 61 , 62 ); female cercus rather broad with l/w ratio: 2.3; subanal plate short, broad, triangular with rounded apex (Fig. 63 ); spermathecae well-sclerotised, smooth, rounded with shallow apical dimple; common base of outer and median arm of surstylus long, slender; outer arm of surstylus basally constricted, apically> 1.5 × width at base, with 6-9 tubercles (Figs 68-70 ); median arm slender, longer than outer arm, with 3-6 spinous setae; inner arm of surstylus two-thirds length of median arm, with apophysis; subepandrial clasper (Figs 69 , 70 ) trapezoidal, basally narrower, mesal apical corner rounded, lateral apical corner pointed; male cercus (Fig. 71 ) with broad lateral extension, slightly concave apically.

Supplementary description.

Below, biometrical data are presented for the series now studied, and compared to the type series. Additional morphological data, as well as a few rectifications, are presented.

Measurements. For the type series of 26 ♀ and 26 ♂, De Meyer (2004) stated body length 5.59 mm (4.95-6.80) and wing length 4.83 mm (4.55-5.10). In Table 3 , measurements and other quantitative characters are presented for the series now studied. In this table, data are presented for females and males separately. The table shows that differences between females and males for quantitative characters are small. The body length and various other measurements are slightly larger in females. In Table 6 , the data for females and males are combined, so that large series can be compared with other Centrioncus species for which large numbers were available. The original measurements of the type series agree well with the means and ranges as presented in the tables: body length 5.55 mm ± 0.09 vs. 5.59 mm and wing length 5.04 mm ± 0.06 vs. 4.83 mm. The measurements confirm C. bytebieri as one of the larger Centrioncus , together with possibly C. angusticercus and C. bururiensis sp. nov. (based on measurements presented in this paper (Tables 6 , 7 ), and Feijen (1983)).

Colour. De Meyer (2004) gave a fine description of the colouration. Characteristic colouration of pleura in prime specimens should be stressed (Figs 55 , 57 ). Yellowish-brown sections include proepisternum, proepimeron, anepimeron with greater ampulla, posterodorsal corner of katepisternum and anterior spot on meron.

Head. Frons (Fig. 56 ) thinly pruinose, laterally densely pruinose, with glossy spots (reduced in some specimens) laterally of ocellar tubercle; length of outer vertical seta 0.38 mm ± 0.01 (n = 16), length of fronto-orbital seta 0.28 mm ± 0.00 (n = 16) (see Tables 6 , 7 ).

Thorax. Scutum densely pruinose, humeral calli and lateral sections behind intrascutal suture thinly pruinose, almost glossy; proepisternum with dorsal third blackish, ventral area brown; anepisternum, anepimeron and greater ampulla brown, leading to striking central brown area on pleura (Figs 55 , 57 ); posterodorsal section of katepisternum brown, other pleura blackish; glossy sections on pleura include ventral edge of anepisternum and large central spot on katepisternum (Fig. 57 ); scutellar spine/scutellum ratio: 0.95 ± 0.01 (n = 16, Table 6 ); scutellar spine/body length ratio: 0.064 ± 0.001 (n = 16); apical seta/scutellar spine ratio: 1.14 ± 0.02 (n = 12); scutellar length/scutellar width (at base) ratio: 0.66.

Wing. Central brownish spot around crossvein r-m in distal tip of cell br and basal fifth of cell r4+5, somewhat extending into cell bm+dm (Figs 3 , 55 ); some infuscation around vein M4 proximal to crossvein dm-m; vein CuA+CuP from vein CuP onward extending under angle of 30° to wing margin in almost straight line (Fig. 3 ); cell cua triangular; vein M4 continuing distal of crossvein dm-m, gradually thinning, very slightly turned downwards towards wing margin.

Legs. Femur 1 on almost distal half of inner side with broad brown stripe which apically broadens (Fig. 55 ); femur 2 with brown stripes on distal third of inner and outer sides, femur 3 with brown stripes on distal quarter of inner and outer sides (Fig. 59 ); femur 1 (Figs 55 , 58 ) incrassate, l/w ratio: 3.30 ± 0.02 (n = 16, Tables 3 , 6 ), femur 1 much less incrassate than in other Centrioncus (see Tables 6 , 7 ); two rows of spinous setae (Fig. 58 ) on distal two-thirds of femur 1 with 6.8 ± 0.2 setae (n = 31, Tables 3 , 6 ), inner row with 3.7 ± 0.1 setae, outer row with 3.1 ± 0.0 setae; two rows of tubercles (Fig. 58 ) on distal three-quarters of femur 1 with 32.7 ± 0.6 tubercles (n = 31, Tables 3 , 6 ), inner row with 15.2 ± 0.3 tubercles, outer row with 17.5 ± 0.4 tubercles; femur 3 ventrodistally with 4.9 ± 0.2 tubercles (n = 32) in single row (Fig. 59 ); setal formula: 3.1, 3.7, 17.5, 15.2, 4.9 agrees with formula of type series given by De Meyer (2004): 3, 3-4, 18, 15, 4.

Preabdomen. Tergites blackish brown, thinly pruinose, posterior edges somewhat paler, more pruinose; tergite 2 with small pale spots in posterolateral corners (Figs 55 , 60 ); tergite 3 with pale posterior band (Fig. 60 ); sternites pale brown; lateral edges of membranous ventral areas with dark lateral spots; sternite 1 rectangular but somewhat constricted mesally (Fig. 72 ); sternite 2 slightly tapering posteriorly, no intersternite present, only mesal anterior edge of sternite 2 slightly more sclerotised (Fig. 72 ); sternite 3 rectangular, sternite 4 trapezoidal, broadening posteriorly (Fig. 72 ); sternite 5 rectangular; sternite 6 short and broad, almost as broad as segment (Fig. 68 ); sternites 1 and 2 glossy, other sternites pruinose (Fig. 72 ); first spiracle in membrane.

Female postabdomen. Seventh spiracle at edge of tergite (Fig. 62 ); anterior sclerite of sternite 7 with w/l ratio: 2.6 (3.1 in De Meyer 2004; fig. 6; see also Table 8 ), glossy on basal third but pruinose posteriorly (Figs 61 , 62 ); posterior sclerite weakly U-shaped, with posterolateral extensions (Figs 61 , 62 ), almost extending to posterior corners of tergite 7, lateral sections with characteristic outward curve, uniformly pruinose; tergite 8 consisting of two oblong plates, narrowly separated mesally, large central sections more sclerotised (Fig. 65 ); tergite 10 (Fig. 65 ) inverted mitre-shaped, extending posteriorly between cerci, clothed in microtrichia and with two pairs of setulae; cercus rather broad, l/w ratio: 2.3 (Fig. 65 , Table 8 ); subanal plate (Figs 63 ) short, broad, almost triangular with rounded apex, ventrally clothed in microtrichia, with ~ 26 setulae on apical half, shape of subanal plate unusual in the genus (compare Fig. 63 vs. Figs 46 , 84 , 105 , and Feijen (1983: figs 47-65); spermathecae well-sclerotised, smooth, rounded with shallow apical dimple (Fig. 64 ), junction of ducts of paired spermathecae V-shaped.

Male postabdomen. Epandrium, cerci and surstyli of additional specimens conform to drawings and description by De Meyer (2004) (Figs 68-70 ); microtrichia on outer side of surstylus shown in Fig. 70 ; common base of outer and median arm of surstylus long and slender; outer arm with 6-9 tubercles; median arm with six dark, spinous setae apically; inner arm of surstylus two-thirds length of median arm; subepandrial clasper (Figs 69 , 70 ) trapezoidal, basally narrower, mesal apical corner rounded, lateral apical corner distinctly pointed, glabrous, with ~ 11 setulae on inner side; cercus (Fig. 71 , Table 8 ) with broad lateral extension distally, with “foot” slightly concave distally, length/greatest width ratio: 1.7 (Table 8 ); ejaculatory apodeme + sac (Fig. 73 , Table 9 ) very large, 11.6% of body length, apodeme club-shaped, basally slender.

Egg. Female from Ngangao carried nine developed and developing eggs in abdomen; eggs (Figs 66 , 67 ) ≤ 1.04 mm in length; slightly elevated longitudinal ridges spanning from anterior pole to posterior pole with fine, nearly hexagonal microstructure between ridges (Fig. 67 ).

Distribution and habitat.

The localities of the type series and the specimens now studied are indicated on the map for Eastern Africa (Fig. 29 ). The distribution appears to be limited to the Taita Hills, a Precambrian mountain range located in the Taita-Taveta County in south-eastern Kenya. These hills consist of three massifs: Dabida (Dawida), Sagalla and Kasigau. Centrioncus bytebieri is only known from the Dabida Massif. No Centrioncus are known from Sagalla, while C. copelandi sp. nov. occurs in Kasigau. The type series was collected in the forest remnants of the Dabida complex in the Ngangao, Chawia and Yale Forests, as well as in the Mbololo Forest. The new specimens also came from Ngangao, Chawia and Mbololo Forests, while as new locations the Fururu and Vuria Forests can now be added. De Meyer (2004) found that his collecting sites were situated from 1400-1800 m, while the specimens now studied were collected from 1680-2162 m. De Meyer added that the species is common and "found on leaves of lower vegetation (shrubs, plants), usually in shaded places in the forests." The gravid female was collected in the last week of January/first week of February, just before the start of the long rains in Kenya. The male collected in the last week of July/first week of August proved to be teneral, so emerging after the end of the long rains.

Remarks.

The additional specimens were largely from the type locality. Male and female genitalia, but also external characters like colour pattern and large size, conform to the description by De Meyer (2004). However, some differences and additions should be indicated. For the pleura, the brown anepimeron and greater ampulla also form part of the large central brown area. The wing has a central wing spot. De Meyer’s description of the posterior sclerite of female sternite 7 was fine but the drawing (fig. 6) shows a rather small sclerite. De Meyer gave a very brief description of the subanal plate. As this plate is very characteristic, it needed redescription. De Meyer described the female cercus as "not so narrow" but gave as l/w ratio: 4.2, which differs from the ratio 2.3 found here. Additional or more detailed illustrations have now been provided for various characters.

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 55 - 60. Centrioncus bytebieri, ♀ 55, 57 - 60 Ngangao Forest 56 Vuria Forest 55 habitus, lateral view 56 head, frontolateral view 57 thorax, lateral view 58 fore femora, ventral view 59 hind femur, inner view 60 abdomen, dorsal view. Scale bars: 0.5 mm.

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).

Figures 68 - 73. Centrioncus bytebieri, ♂, Vuria Forest 68 synsternite 7 + 8, epandrium, surstyli, lateral view 69 subepandrial clasper and surstylus, inner view 70 subepandrial clasper and surstylus, outer view 71 cercus, posterior view 72 sternites 1 - 5, ventral view 73 ejaculatory apodeme + sac. Scale bars: 0.2 mm (68, 72); 0.1 mm (69 - 71, 73).

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 84 - 87. Centrioncus copelandi sp. nov., ♀, paratype, Kasigau Mtn 84 subanal plate, ventral view 85 spermathecae 86 egg 87 egg, detail of external microstructure. Scale bars: 0.1 mm (84, 85, 87); 0.2 mm (86).

Figures 101 - 105. Centrioncus crassifemur sp. nov., ♀, holotype, N'dalatando 101 sternites 1 - 5, ventral view 102 sternites 6 - 8, subanal plate, cerci, ventral view 103 tergites 8, 10, cerci, dorsal view 104 sternite 7, ventral view 105 subanal plate, ventral view. Scale bars: 0.5 mm (101, 102); 0.1 mm (103 - 105).