Centrioncus aberrans Feijen, 1983

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 aberrans Feijen

Figs 1 , 9-12 , 13-15 , 16-20 , 21-24 , 25-28 , 29 , 30

Centrioncus aberrans Feijen, 1983: 84.

Centrioncus sp. Feijen 1983: 87 (this specimen from Rwanda, Lac Gando, was only cursorily inspected, but could now be studied in detail).

Type material.

Uganda: holotype, ♂, Kilembe, Ruwenzori Range, [0°11'51"N, 30°0'47"E], 1500 m, F.W. Edwards (NHMUK). Paratypes: 1 ♀, 1 ♂, same data as holotype (NHMUK).

Material studied.

Kenya: 8 ♀, 12 ♂, Mount Elgon, nr Elephant Cave ( Kitum cave ), [1°1'56.84"N, 34°45'28.94"E, 2350 m], 22.iii.1988, H.R. Feijen (RMNH); 1 ♂, Saiwa Swamp, [1°5'43.60"N, 35°6'59.45"E, 1870 m], 23.iii.1988, H.R. Feijen (RMNH); 3 ♂, Rift Valley Province , Timboroa Forest (compt. 9), malaise traps, indigenous Afromontane forest , 00°04.092'S, 35°30.909'E, 2628 m, 14-16.iv.2011, A.H. & M.K. Kirk-Spriggs (BMSA); 1 ♀, Rift Valley Prov. , Lake Nakuru N.P., malaise trap, Acacia xanthophloea habitat, 0.35130°S, 36.05795°E, 1796 m, 3-17.iii.2006, R. Copeland (ICIPE) ; Rwanda: 1 ♂, N. Kivu, Lac Gando , 1°36'S, 29°24'E, 2400 m, 25.xii.1925, H. Schouteden (MRAC) ; Rwanda & DR Congo [as Zaire]: 2 ♀, x.1993, Thomas Wagner , canopy fogging on specific trees (FBUB) [According to Dr Wagner (pers. comm.), there are two options for the collection site: Rwanda, Cyamudongo, Nyakabuye, 2°34'S, 28°59'E, 1750 m, montane rain forest or DR Congo Irangi, Kivu-Sud, 1°54'S, 28°27'E, 950 m, rain forest. The distance between the two sites is 95 km in a straight line.]. In total 12 ♀ and 19 ♂ were studied .

Diagnosis.

Centrioncus aberrans can be recognised by its mesally depressed, pruinose frons with two small glossy spots; glossy, blackish brown collar; pruinose, blackish brown scutum; pruinose, brown scutellum with two dark spots; brown scutellar spines; blackish brown pleura, but propleuron, anterior half and posteroventral corner of anepisternum, and dorsal “knob” of anepimeron chestnut brown (Fig. 12 ); scutellar spine/scutellum ratio: 0.95; apical seta/scutellar spine ratio: 1.13; brown fore femur on distal quarter dark brown on both sides, strongly incrassate (l/w ratio: 2.75) with ~ 35.5 tubercles; medium-sized central wing spot largely in basal quarter of cell r4+5, extending into cells br and bm+dm (Fig. 1 ); tergites dark brown, thinly pruinose; sternite 4 rectangular (Fig. 13 ), sternite 5 trapezoidal; sternite 6 a short, broad, trapezoidal sclerite, 1.6 × the width of sternites 1-5; female 7th spiracle half in/half out of tergite; anterior sclerite of female sternite 7 rectangular, w/l ratio: ~ 5.3 (Figs 13 , 14 ); posterior sclerite of female sternite 7 large, weakly sclerotised and rectangular with more sclerotised anterolateral sections; very elongate female cercus with l/w ratio: ~ 5.1; pentagonal subanal plate; smooth spermathecae with some tiny pustules and small dimple surrounded by ridge-like ring; outer and median arms of surstylus broadly joined, with short broad common base (Figs 21-24 ); outer arm triangular, apically tapering, base twice as wide as apex, rounded apically, with four or five tubercles; median arm broader and longer than outer arm, parallel-sided, with five or six spinous setae; inner arm half the length of median arm, with apophysis; subepandrial clasper (Figs 25-28 ) with strong basal constriction, rectangular with lateral apical corner a bit extended and rounded, mesal basal corner square; male cercus (Fig. 17 ) slender, somewhat broadening from base to apex, without distal lateral extension.

Supplementary description.

Below, biometrical data are given for the much larger series now studied, as compared to the type series. Additional morphological data, as well as some rectifications, are presented.

Measurements. For the small type series of 1 ♀ and 2 ♂ Feijen (1983) gave for width of head in ♀ 1.12 mm and in ♂ 1.24 and 1.15 mm, body length in ♀ 4.9 mm and in ♂ 5.2 and 5.0 mm, wing length in ♀ 4.4 mm and in ♂ 4.7 and 4.4 mm, and length of scutellar spine in ♀ 0.26 mm and in ♂ 0.27 and 0.26 mm. In Table 2 , measurements and other quantitative characters are presented for the much larger series now studied. In this table, data are presented for females and males separately. From this table, the differences between females and males for quantitative characters are marginal. The body length is slightly larger in the male. In Tables 6 , 7 the data for females and males are combined, so that large series can be compared with the other Centrioncus species for which large numbers were available. In the other three species for which large series could be measured, the females were, on the average, clearly somewhat larger. The original measurements of the type series of C. aberrans fall well within the ranges as presented in Table 2 .

Colour. Most of the specimens now studied were not so dark as those of the type series. These latter three specimens were therefore probably somewhat discoloured, a common tendency in the Centrioncinae ( Feijen 1983). The overall colour pattern can be seen in Figs 9-12 .

Head. Frons dark brown with anterior edge paler brown (in type-series frons almost uniformly brown), pruinose except two small glossy spots on either side of ocellar tubercle (Figs 10 , 11 ); face, gena and mouthparts pruinose, yellowish brown, palpus blackish; occiput uniformly blackish brown in type series ( Feijen 1983), dark brown with more yellowish-brown ventral quarter in additional specimens; length of outer vertical seta 0.36 mm ± 0.00 (n = 17); length of fronto-orbital seta 0.22 mm ± 0.01 (n = 16).

Thorax. Collar glossy blackish brown (Fig. 10 ); scutum blackish brown, densely pruinose, humeral calli (postpronotal lobes) less pruinose (Figs 9 , 12 ); scutellum pruinose, dark brown in “greasy” specimens but brown with two vague darker spots in other specimens; scutellar spines brown; pleura (Fig. 12 ) mostly blackish brown, propleuron, anterior half and posteroventral corner of anepisternum and dorsal “knob” of anepimeron chestnut brown (pleura uniformly blackish brown in type series); scutellar spines diverging at angle of ~ 45° (type-series 40°); scutellar spine/scutellum ratio: 0.78 ± 0.01 (n = 18); scutellar spine/body length ratio: 0.056 ± 0.001 (n = 22); apical seta/scutellar spine ratio: 1.13 ± 0.01 (n = 10); scutellar length/scutellar width (at base) ratio: 0.64.

Wing. Subcostal cell not visible in most specimens, visible in one specimen from Rwanda and one specimen of Mt. Elgon; vein CuA+CuP from vein CuP onward slightly curving downward under angle of 30° to wing margin (Fig. 1 ); central wing spot distinct, medium-sized, largely in basal quarter of cell r4+5, extending into cells br and bm+dm; vague infuscation along vein M4; cell cua in between triangular and rectangular (Fig. 1 ).

Legs. Fore femur (Fig. 9 ) yellowish with distal quarter on both sides dark brown (only Lac Gando specimen on inner side with distinct brown stripe on distal third); fore femur strongly incrassate, l/w ratio: 2.75 ± 0.01 (n = 22), two rows of spinous setae on distal two-thirds with 9.0 ± 0.1 setae (n = 45), inner row with 4.9 ± 0.0 setae and outer row with 4.1 ± 0.0 setae, two rows of tubercles on distal three-quarters with 35.4 ± 0.5 tubercles (n = 42), inner row with 17.2 ± 0.2 tubercles and outer row with 18.2 ± 0.3 tubercles; hind femur distally with 6.5 ± 0.2 (n = 46) tubercles in single row but in two specimens one tubercle placed in second row; setal formula (sensu Feijen 1983) of 4.1, 4.9, 18.2, 17.2, 6.5 vs. formula of type-series: 4.0, 5.2, 16.8, 15.2, 6.5.

Preabdomen. Dorsally dark brown, thinly pruinose; posterolateral corners of tergite 2 paler brown; sternites 1-6 brown, thinly pruinose, sternite 2 more glossy; sternite 1 rectangular, constricted on meson (Fig. 13 ); sternite 2 anteriorly with mesally narrow, strongly sclerotised intersternite 1-2, laterally with thin extensions connected to main sternite 2; sternites 3 and 4 rectangular (Fig. 13 ), sternite 5 trapezoidal, broadening posteriorly; sternite 6 short, broad, trapezoidal, broadening posteriorly, ~ 1.6 × width of sternites 1-5.

Female postabdomen. Seventh spiracle half in/half out of tergite or touching tergite (Fig. 14 ); anterior sclerite of sternite 7 with w/l ratio: ~ 5.3 (5.2-5.4); flies from Mt Elgon with weakly sclerotised rectangular plate (with rounded anterior corners) of posterior sclerite of sternite 7, as in female paratype with two large more sclerotised sections joined anteromesally (Figs 13 , 14 ); spermathecae as in paratype (spherical with small apical dimple with small ring); junction of ducts of paired spermathecae T-shaped (Figs 13 , 15 ).

Male postabdomen. Epandrium yellowish brown, darker brown anteriorly (Fig. 16 ) (uniformly brown in type series); qualitative characters conform with original description; surstylus of paratype ♂ (Fig. 21 ) identical to specimens from Mt Elgon, Lac Gando and Timboroa forest (Figs 22-24 ); narrow cercus, without apical lateral extension, length/greatest width ratio: 2.6 (Fig. 17 , Table 8 ); subepandrial clasper of males from three localities (Figs 26-28 ) similar to paratype (Fig. 25 ); epandrial fold (periandrial fold sensu Feijen (1983)) consists of one single piece, with inner section of fold not detached to form epandrial sclerite (stated as detached in the original description); quantitative characters agree well; outer arm of surstylus with 4-5 tubercles in type-series and specimens from Kenya and Rwanda (Figs 21-24 ); median arm of surstylus with 6 stout spinous setae in type series, and only 5 spinous setae in specimens from Mount Elgon, Timboroa, and Rwanda (Figs 21-24 ); basal setulae on outer arm and setulae on inner arm distinctly larger in Kenya specimens (Figs 22 , 24 ); ejaculatory apodeme + sac in all four males (from Rwanda, Mount Elgon, and Timboroa Forest) (Figs 18-20 , Table 9 ) very large (9.3, 10.1, 10.1 and 11.2% of body length, respectively) (shorter in paratype).

Distribution and habitat.

In the map of Eastern Africa (Fig. 29 ), the collection localities for C. aberrans are indicated. The eastern branch of the Great Rift Valley appears to form a barrier between the populations of C. aberrans and C. decoronotus . The two females collected in DR Congo/Rwanda are not indicated on the map. These two flies were collected by canopy fogging of individual trees. The methodology used for this fogging is explained in Wagner (2000, 2001). Funnel-shaped sheets were attached to the trees at waist height for collecting the dropping insects. Dr Wagner (pers. comm.) explained that "The lowest branches hit by the fog were about 3 metres [high] and it reaches usually ≤ 10 m."

Feijen (1983) indicated the habitat for Centrioncus and Teloglabrus was low shrubs and herbaceous plants. We collected the flies at heights of ~ 20-60 cm from ground level. The results of the canopy fogging trials possibly indicate that Centrioncus flies might also occur at higher levels in the trees, though disturbance of the flies or descending insecticide might form alternative explanations. Nothing is known about where oviposition occurs and larval feeding, so the possibility of breeding in the tree canopy cannot be excluded. The flies of C. aberrans from Timboroa Forest in Kenya were collected in a malaise trap. The height at which these flies were trapped is more in line with the habitat indicated by Feijen (1983). The Timboroa habitat is illustrated in Fig. 30 .

Remarks.

Given the unusually large range of distribution of this Centrioncus species, special care was taken to examine and compare defining characters such as surstylus, subepandrial clasper, male cercus and female sternite 7 for flies from the regions involved: western Uganda, western Rwanda, western and more central Kenya (Fig. 29 ). Comparisons of surstyli (Figs 21-24 ) and subepandrial claspers (Figs 25-28 ) lead to the conclusion that they are largely similar. For the surstyli, the general shape, number of tubercles and number of spinous setae correspond well. Also, the very specific female sternite 7 (Figs 13 , 14 ) is very similar to the female paratype. The subepandrial clasper of the paratype (Fig. 25 ) appears less broad, but this is caused by it being slightly tilted to the right during the preparation. While comparing the shapes of the surstyli, care must be taken to present these three-dimensional structures as much as possible in the same plane. In the drawing of the surstylus of the paratype male (Fig. 21 ), the median arm is slightly tilted upward, so this arm appears somewhat shorter. Likewise, the inner arm of the surstylus in the Lac Gando specimen (Fig. 23 ) is somewhat tilted and so appears a bit different. In addition, small differences in shape of the three arms and size of setulae are observed and it could be argued that this species is in a very early phase of allopatric speciation. However, if one looks at the major differences for these defining characters between the Centrioncus species (Figs 51 , 69 , 88 , 122 , 138 , 150 ; Feijen 1983), the conclusion can be drawn that all specimens examined across the large distribution range belong to one species, C. aberrans .

Figures

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

Figure 30. Centrioncus aberrans, Kenya, Timboroa Forest, collection site, 2011. Photograph by A. H. Kirk-Spriggs.

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 9 - 12. Centrioncus aberrans 9 Mount Elgon, ♀, habitus, lateral view 10 - 12 Timboroa Forest, ♂ 10 head, dorsal view 11 head, frontal view 12 thorax, lateral view. Arrows indicate glossy spots on frons. Scale bars: 0.5 mm.

Figures 13 - 15. Centrioncus aberrans, Mount Elgon, ♀ 13 abdomen, ventral view 14 sternite 7, ventral view 15 spermathecae. Scale bars: 0.5 mm (13); 0.1 mm (14, 15).

Figures 16 - 20. Centrioncus aberrans, ♂ 16, 20 Timboroa Forest 17, 18 Mount Elgon 19 Lac Gando 16 epandrium with surstyli, posterior view 17 cercus, posterior view 18 - 20 ejaculatory apodeme. Scale bars: 0.1 mm.

Figures 21 - 24. Centrioncus aberrans, ♂, surstylus, inner view 21 paratype. Uganda. Kilembe 22 Kenya, Mount Elgon 23 Rwanda, Lac Gando 24 Kenya, Timboroa Forest. Scale bar: 0.1 mm.

Figures 25 - 28. Centrioncus aberrans, ♂, subepandrial clasper, outer view 25 paratype, Uganda. Kilembe 26 Kenya, Mount Elgon 27 Rwanda, Lac Gando 28 Kenya, Timboroa Forest. Scale bar: 0.1 mm.

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 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 88 - 91. Centrioncus copelandi sp. nov., ♂, holotype, Kasigau Mtn 88 surstylus, inner view 89 cercus, posterior view 90 subepandrial clasper, posterior view 91 ejaculatory apodeme + sac. Scale bars: 0.1 mm.

Figures 122 - 125. Centrioncus decoronotus, ♂, Ol Doinyo Orok 122 left subepandrial clasper and surstylus, inner view 123 cercus, posterior view 124 right subepandrial clasper, posterior view 125 ejaculatory apodeme + sac. Scale bars: 0.1 mm (122 - 124); 0.2 mm (125).

Figures 136 - 138. Centrioncus jacobae, ♂, Mt Soche 136 holotype, abdomen, hind femur, lateral view 137 epandrium, surstyli, posterior view 138 paratype, subepandrial clasper and surstylus, inner view. Scale bars: 0.5 mm (136); 0.1 mm (137, 138).

Figures 150, 151. Centrioncus prodiopsis, ♂, lectotype, Kibongoto 150 surstylus, inner view 151 subepandrial clasper and base of surstylus, posterior view. Scale bars: 0.1 mm.