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

publication ID

https://dx.doi.org/10.3897/zookeys.1144.95619

publication LSID

lsid:zoobank.org:pub:565B46A4-C01B-4542-9635-6F3ED6472747

persistent identifier

https://treatment.plazi.org/id/4453C226-2EEA-5716-8230-373D68A5F8C6

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scientific name

Centrioncus aberrans Feijen
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Centrioncus aberrans Feijen View in CoL

Figs 1 View Figures 1–4 , 9-12 View Figures 9–12 , 13-15 View Figures 13–15 , 16-20 View Figures 16–20 , 21-24 View Figures 21–24 , 25-28 View Figures 25–28 , 29 View Figure 29 , 30 View Figure 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) GoogleMaps ; Rwanda: 1 ♂, N. Kivu, Lac Gando , 1°36'S, 29°24'E, 2400 m, 25.xii.1925, H. Schouteden (MRAC) GoogleMaps ; 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 GoogleMaps .

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 View Figures 9–12 ); 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 View Figures 1–4 ); tergites dark brown, thinly pruinose; sternite 4 rectangular (Fig. 13 View Figures 13–15 ), 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 View Figures 13–15 , 14 View Figures 13–15 ); 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 View Figures 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 View Figures 25–28 ) with strong basal constriction, rectangular with lateral apical corner a bit extended and rounded, mesal basal corner square; male cercus (Fig. 17 View Figures 16–20 ) 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 View 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 View Table 6 , 7 View Table 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 View 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 View Figures 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 View Figures 9–12 , 11 View Figures 9–12 ); 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 View Figures 9–12 ); scutum blackish brown, densely pruinose, humeral calli (postpronotal lobes) less pruinose (Figs 9 View Figures 9–12 , 12 View Figures 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 View Figures 9–12 ) 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 View Figures 1–4 ); 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 View Figures 1–4 ).

Legs. Fore femur (Fig. 9 View Figures 9–12 ) 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 View Figures 13–15 ); 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 View Figures 13–15 ), 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 View Figures 13–15 ); 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 View Figures 13–15 , 14 View Figures 13–15 ); spermathecae as in paratype (spherical with small apical dimple with small ring); junction of ducts of paired spermathecae T-shaped (Figs 13 View Figures 13–15 , 15 View Figures 13–15 ).

Male postabdomen. Epandrium yellowish brown, darker brown anteriorly (Fig. 16 View Figures 16–20 ) (uniformly brown in type series); qualitative characters conform with original description; surstylus of paratype ♂ (Fig. 21 View Figures 21–24 ) identical to specimens from Mt Elgon, Lac Gando and Timboroa forest (Figs 22-24 View Figures 21–24 ); narrow cercus, without apical lateral extension, length/greatest width ratio: 2.6 (Fig. 17 View Figures 16–20 , Table 8 View Table 8 ); subepandrial clasper of males from three localities (Figs 26-28 View Figures 25–28 ) similar to paratype (Fig. 25 View Figures 25–28 ); 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 View Figures 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 View Figures 21–24 ); basal setulae on outer arm and setulae on inner arm distinctly larger in Kenya specimens (Figs 22 View Figures 21–24 , 24 View Figures 21–24 ); ejaculatory apodeme + sac in all four males (from Rwanda, Mount Elgon, and Timboroa Forest) (Figs 18-20 View Figures 16–20 , Table 9 View 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 View Figure 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 View Figure 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 View Figure 29 ). Comparisons of surstyli (Figs 21-24 View Figures 21–24 ) and subepandrial claspers (Figs 25-28 View Figures 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 View Figures 13–15 , 14 View Figures 13–15 ) is very similar to the female paratype. The subepandrial clasper of the paratype (Fig. 25 View Figures 25–28 ) 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 View Figures 21–24 ), 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 View Figures 21–24 ) 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 View Figures 50–54 , 69 View Figures 68–73 , 88 View Figures 88–91 , 122 View Figures 122–125 , 138 View Figures 136–138 , 150 View Figures 150, 151 ; Feijen 1983), the conclusion can be drawn that all specimens examined across the large distribution range belong to one species, C. aberrans .

Kingdom

Animalia

Phylum

Arthropoda

Class

Insecta

Order

Diptera

Family

Diopsidae

Genus

Centrioncus

Loc

Centrioncus aberrans Feijen

Feijen, Hans R. & Feijen, Cobi 2023
2023
Loc

Centrioncus aberrans

Feijen 1983
1983
Loc

Centrioncus

Speiser 1910
1910