Centrioncus decoronotus 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 decoronotus Feijen

Figs 6 , 29 , 112-116 , 117 , 118-121 , 122-125 , 153

Centrioncus decoronotus Feijen, 1983: 76; McAlpine 1997: 175, 2011: 150; De Meyer 2004: 28; Marshall et al. 2009: 6; Lonsdale 2020: 6, figs 153-159, 405, 423, 425; Feijen and Feijen 2021, figs 2, 29.

Centrioncus prodiopsis : Steyskal 1970: 326 (in part, male description and figs 3, 4).

Type material.

Kenya, holotype ♂, Naivasha [0°41'40"S, 36°22'47"E], vii.1937, H.J.A. Turner (NHMUK). Paratypes: 1 ♀, 1 ♂, same data as holotype; 1 ♀, 1 ♂, Thomson’s Falls [now Nyahururu Falls, 0°2'38.98"N, 36°22'13.04"E], x.1934, F.W. Edwards (NHMUK); 1 ♂, Chania Falls, Aberdare range [0°27'16.70"S, 36°43'1.28"E], x.1934, F.W. Edwards (NHMUK); 1 ♀, Ngong [1°21'22"S, 36°40'8"E], ix.1940, G. van Someren (NHMUK).

Material studied.

Kenya: 27 ♀, 25 ♂, Naro Moru River , [0°9'22.93"S, 37°0'50.45"E, 1950 m], 20.vii.1987, H.R. Feijen (RMNH); 6 ♀, 6 ♂, Limuru nr Mrs Mitchels tea plantation, Rain forest , Kiambethu Tea Plantation , [1°7'3.18"S, 36°40'58.11"E, 2167 m], 3.ix.1986, Cobi Feijen (RMNH); 2 ♀, 2 ♂, nr Namanga Tanzania [but in Kenya], Ol Doinyo Orok forest , [~ 2°31'S, 36°47'E, ~ 1800 m], 0. iii.1986, J. Muhangani (RMNH); 1 ♀, 1 ♂, Thomson’s falls, Nyahururu, [0°2'38.98"N, 36°22'13.04"E, 2329 m], 20.iii.1988, H.R. Feijen (RMNH); 3 ♀, 3 ♂, Nyahuru (ru), Upper Imenti Forest , Meru Distr. E. Kenya, [0°3'0"N, 37°31'59"E], vii.1973, E. Balyetagara (CNC); 2 ♀, 3 ♂, Laikipia Co., Thomson’s Falls env. (= Ngare Naro forest ), 0.047°N, 36.377°E, 25.xi.2012, D. Gavryushin (ZMUM); 3 ♀, 1 ♂, Laikipia Co., Thomson's Falls env ., 0.047°N, 36.377°E, 21-23.xii.2013, N. Vikhrev (ZMUM); many (photograph), Ngare Naro forest (near Thomson’s Falls), 27.xi.2012, D. Gavryushin; 2 ♀, 2 ♂, Central Province , Katura Forest , Nairobi , shaded mixed upland indigenous forest , 1°14.504'S, 36°49.452'E, 1720 m, 23.iv.2011, A.H. & M.K. Kirk-Spriggs (BMSA); 3 ♀, 1 ♂, Eastern Prov., Nyambene Hills, Itieni forest , at bottom, malaise trap, edge indigenous forest , 0.24433°N, 37.87016°E, 2142 m, 1 ♀ 1 ♂ 2-16.x.2011, 1 ♀ 18.ix-2.x.2011, 1 ♀ 15-29.xi.2011, R. Copeland (ICIPE); 1 ♀, Central Prov., Ngong road forest, Nairobi , fogging , 1°18'57"S, 36°44'27"E, ~ 1830 m, 12-14.ii.1999, T. Wagner (ICIPE); 2 ♀, 3 ♂, Eastern Prov., Njuki-Ini Forest , near forest station, sweep net, edge indigenous forest , 0.51660°S, 37.41843°E, 1455 m, 13.ii.2011, R. Copeland (ICIPE); 1 ♀, 2 ♂, Gatama (i)yu forest, near fishing camp, malaise trap , 0°58.68'S, 36°41.62'E, ~ 2246 m, 20-27.iii.1999, R. Copeland (ICIPE). In total 53 ♀ and 49 ♂ were examined.

Diagnosis.

Centrioncus decoronotus can be recognised by the mesally depressed, pruinose frons with glossy spots; glossy collar; scutum with configuration of blackish brown and brown (Figs 112 , 113 , 117 ), basic colour chestnut brown (including humeral calli), blackish sutures around humeral calli, blackish mesal stripe on anterior half, square, mesal, blackish area posteriorly of intrascutal sutures; scutellum brown, dorsally darker, scutellar spines brown; pleura blackish brown (Figs 113 , 117 ) with chestnut brown anterodorsal anepisternum, greater ampulla and posterior anepimeron; scutellar spine/scutellum ratio: 0.90; apical seta/scutellar spine ratio: 0.91; yellowish brown, strongly incrassate fore femur (l/w ratio: 2.89) with ~ 34.5 tubercles; brown stripe dorsally on distal half of inner side (Figs 113 , 114 ); large central wing spot (Fig. 6 ), mainly in basal section of cell r4+5 till just apically of crossvein dm-m, extending into cell br, cell r2+3 and cell bm+dm; tergites dark brown, thinly pruinose, posterolateral corners whitish pruinose; sternite 4 rectangular, laterally two more sclerotised sections, anteriorly 2 pairs of tiny heavily sclerotised spots (Fig. 118 ); sternite 5 broadening posteriorly, laterally more sclerotised, 1 pair of strongly sclerotised spots anteriorly; sternite 6 trapezoidal, posteriorly 1.6 × as wide as sternites 1-4, two more sclerotised plates anteriorly; female tergite 7 with serrated lateral edges; female 7th spiracle in tergite; anterior sclerite of female sternite 7 short (Table 8 ), w/l ratio: ~ 3.9 (Fig. 119 ); posterior sclerite of female sternite 7 U-shaped, posterior apices sometimes slightly broadening (Fig. 119 ); female cercus rather elongate with l/w ratio: 3.6; subanal plate pentagonal, laterally convex, apex acuminate; spermathecae round, somewhat wrinkled, distinct dimple, some tiny tubercles (Fig. 120 ); common base of outer and median arm of surstylus long, slender; outer arm rounded, deeply constricted near median arm, largest width 1.8 × width at base, 4-6 tubercles apically (Fig. 122 ); median arm slender, rod-shaped, much longer than outer arm, three or four spinous setae apically; inner arm apically acuminate, shorter and narrower than median arm, no apophysis; subepandrial clasper triangular, basal two-thirds narrow, medial apical corner angular, lateral corner extended (Figs 122 , 124 ); cercus (Fig. 123 ) with broad lateral extension on distal third, apically slightly concave.

Supplementary description.

The 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. Various aspects of the morphology are now illustrated by photographs, while line drawings are presented for flies from Ol Doinyo Orok, a location distant from the type location.

Measurements. For type series of 3 ♀ and 4 ♂, Feijen (1983) provided the following measurements: body length ♀ 5.3 mm and ♂ 5.2 mm, head width ♀ 1.23 mm and ♂ 1.17 mm, wing length ♀ 5.0 mm and ♂ 4.7 mm, scutellar spine length ♀ 0.36 mm and ♂ 0.31 mm. For the much larger series now available, 22 ♀ and 22 ♂ were measured in more detail. In Table 4 , measurements and other quantitative characters are presented for this series. In this table, data are presented for females and males separately. The table shows that differences between females and males for quantitative characters are marginal. The body length and various other measurements are slightly larger in the females. 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. The original measurements of the type series fall well within the ranges provided here: body length 5.15 mm ± 0.04 (range 4.64-5.61, n = 44), head width 1.14 mm ± 0.01 (range 1.02-1.24, n = 44), wing length 4.51 mm ± 0.03 (range 4.09-5.00, n = 39), scutellar spine length 0.33 mm ± 0.00 (range 0.29-0.37, n = 44).

Colour. The specific epithet decoronotus refers to the colourful notum of the mesothorax with its pattern of brown and blackish brown. This pattern is shown well in the fly from the Thomson’s Falls (Fig. 112 ), but is much less pronounced to almost absent in flies from Katura Forest. This is not only due to preservation techniques, but is present in live specimens as can be observed in photographs of live flies from Ngare Naro forest (near Thomson’s Falls) where the pattern is also less pronounced (Fig. 117 ).

Head. Frons mesally depressed, pruinose with glossy spots lateral to ocellar tubercle (Fig. 116 ), face yellowish brown; occiput mainly blackish brown, ventral edge of occiput and postgena yellowish (Fig. 113 ), thinly pruinose, with median occipital sclerite densely pruinose; length of outer vertical seta 0.34 mm ± 0.00 (n = 35, Tables 4 , 7 ); length of fronto-orbital seta 0.22 mm ± 0.00 (n = 35). In highly enlarged photographs, mid facial region densely microtrichose, with row of microtrichia near eye margin ( McAlpine 1997: figs 21, 22) (see also Fig. 116 ).

Thorax. Collar glossy blackish brown (Figs 112 , 117 ); scutum and pleura show typical configuration of blackish brown and brown (Figs 112 , 113 , 117 ); humeral callus brown (not blackish brown as described by Feijen (1983: fig. 7)); scutellar spine/scutellum ratio: 0.90 ± 0.01 (n = 44, Tables 4 , 7 ); scutellar spine/body length ratio: 0.063 ± 0.001 (n = 44); apical seta/ scutellar spine ratio: 0.91 ± 0.01 (n = 21, range 0.83-1.03; Table 7 ); scutellar length/scutellar width (at base) ratio: 0.64; supra-alar carina with supra-alar seta illustrated by McAlpine (1997: fig. 35), seta difficult to see in Figs 112 , 113 .

Wing. Large, central wing spot, mainly in basal section of cell r4+5, extending into cell br, cell r2+3 and cell bm+dm (Fig. 6 ); distinct infuscation along central section of vein M4; some variability in intensity of central spot, specimens from Katura forest have, for instance a darker spot than specimens from Naro Moru; two vague apical wing spots mentioned by Feijen (1983) in cells r2+3 and r4+5 often not visible; vein M4 continuing distal of crossvein dm-m in straight line to wing margin; vein CuA+CuP from vein CuP onward extending under angle of 30° to wing margin in almost straight line; cell cua triangular.

Legs. Femur 1 with distinct brown stripe (Figs 113 , 114 , 117 ) dorsally on distal half of inner side, not vague as stated by Feijen (1983); femur 1 strongly incrassate, l/w ratio: 2.89 ± 0.01 (n = 43, Tables 4 , 7 ); two rows of spinous setae (Fig. 114 ) on distal two-thirds of femur 1 with 8.4 ± 0.1 setae (n = 72, Tables 4 , 7 ), inner row with 4.5 ± 0.1 setae, outer row with 3.9 ± 0.0 setae; two rows of tubercles (Fig. 114 ) on distal three-quarters of femur 1 with 34.5 ± 0.3 tubercles (n = 71, Tables 4 , 7 ), inner row with 16.4 ± 0.1 tubercles and outer row with 18.1 ± 0.2 tubercles; femur 3 (Fig. 115 ) distally with 4.9 ± 0.1 tubercles (n = 83, Tables 4 , 7 ) in single row, except for 1 ♀ and 1 ♂ with each one tubercle in second row; setal formula 3.9, 4.5, 18.1, 16.4, 4.9 agrees well with formula of type-series given by Feijen (1983): 4.0, 4.3, 17.8, 17.0, 4.9.

Preabdomen. Tergites blackish brown, thinly pruinose, with whitish pruinose posterolateral corners; female tergite 7 less dark and glossier; posterolateral corners of tergite 2 more densely pruinose; sternites pale brown; membranous ventral areas with large dark lateral spots (Fig. 117 ); sternite 1 rounded rectangular, anteriorly strongly constricted mesally (Fig. 118 ); intersternite 1-2 dark, laterally acuminate, with thin lateral connections to main sternite 2; sternites 2-4 rectangular (Fig. 118 ), slender, more or less of equal width; sternite 5 somewhat broadening posteriorly; sternite 6 trapezoidal, posteriorly ~ 1.6 × as wide as sternites 1-4 (Fig. 118 ); sternite 4 laterally with two ill-defined more sclerotised sections and two pairs of small heavily sclerotised sections anteriorly (Fig. 118 ); sternite 5 laterally with more sclerotised sections, anteriorly with pair of strongly sclerotised plates; sternite 6 more vaguely sclerotised laterally and anteriorly with pair of strongly sclerotised plates; sternites 1 and 2 glossy, sternite 1 with some microtrichia laterally, sternite 2 with some microtrichia in posterolateral corners; sternites 3-6 pruinose.

Female postabdomen. Tergite 7 with slightly serrated lateral edges (Fig. 119 ); 7th spiracle in tergite; anterior sclerite of sternite 7 relatively short with w/l ratio: 3.9 (Table 8 ); posterior sclerite U-shaped; anterior and posterior sclerites of sternite 7 of ♀ from Ol Doinyo Orok forest similar to paratype illustrated by Feijen (1983), but posterolateral sections of posterior sclerite somewhat expanded (Fig. 119 ); cercus rather elongate, l/w ratio: 3.6 (Table 8 ); spermathecae of Ol Doinyo Orok ♀ (Fig. 120 ) similar to type series.

Male postabdomen. Genitalia identical with illustrations by Feijen (1983) but can be annotated as follows: for ♂ from Ol Doinyo Orok forest, surstylus, subepandrial clasper, cercus and ejaculatory apodeme + sac illustrated (Figs 122-125 ), as location is furthest removed from localities of type series; median arm of surstylus curved, long (Fig. 122 ) (due to curve median arm appears slightly shorter in Feijen (1983: fig. 140); outer arm of surstylus with 4 tubercles (and 1 underdeveloped one) (average of 6.0 tubercles (n = 4) in Feijen (1983)); median arm and basal half of outer arm clothed in microtrichia on outer side; 3-dimensional character of subepandrial clasper with small differences (compare Figs 122 , 124 vs. Feijen 1983: fig. 141), very constricted basal section of subepandrial clasper, mentioned by Feijen (1983), also found in Ol Doinyo Orok ♂; cercus (Fig. 123 , Table 8 ) with broad lateral extension on distal third, apically slightly concave, length/greatest width ratio: 1.4; ejaculatory apodeme + sac/length of body ratio: 16.5% (paratype from Chania Falls with ratio 16.3%) (Figs 125 , 153 ).

Egg. Female from Ol Doinyo Orok forest with two almost fully developed eggs in abdomen. Eggs measured respectively 0.99 mm and 1.00 mm in length with longitudinal ridges spanning from anterior pole to posterior pole; in addition, more simple “lines”. Ridges (indicated with R) with tiny elongate pits along their length, while lines (indicated with L) form more integral part of roughly hexagonal microstructures between ridges (Fig. 121 ).

Distribution and habitat.

The collecting localities are shown on the map for Eastern Africa (Fig. 29 ). Centrioncus decoronotus was now found at altitudes varying from 1455-2329 m. Feijen (1983) reported it as occurring between 1200-2350 m. The eastern branch of the Great Rift Valley appears to form a barrier between C. decoronotus and C. aberrans . The gravid female was collected in March at the beginning of the long rains.

Remarks.

Feijen (1983) described the lateral sides of female tergite 7 as "rather irregular", but showed the same serrated edges in his fig. 28, as now found in the specimen from Ol Doinyo Orok (Fig. 119 ). Other species of Centrioncus or Teloglabrus with serrated sides of tergite 7 are not known. The paratype from Thomson’s Falls had with 16.3% the highest ejaculatory apodeme + sac/length of body ratio. The Ol Doinyo Orok ♂ had with 16.5% a similar giant ejaculatory apodeme + sac (Table 9 ).

Figures

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

Figure 117. Centrioncus decoronotus, ♂, Nyahururu, Ngare Naro Forest. Photograph by D. Gavryushin.

Figures 5 - 8. Centrioncus, dorsal view of wings 5 ♀, holotype, C. crassifemur sp. nov., N'dalatando 6 ♂, C. decoronotus Njuki-Ini Forest 7 ♂, C. jacobae Mount Soche 8 ♀, C. prodiopsis, Oloitokitok. Scale bars: 0.5 mm.

Figures 112 - 116. Centrioncus decoronotus 112, 113 ♀, Thomson's Falls 114, 115 ♂, Itieni Forest 116 ♂, Katura Forest 112 thorax, dorsal view 113 head, thorax, lateral view 114 fore femur, inner view 115 hind femur, inner view 116 head, frontolateral view. Scale bars: 0.2 mm (112, 114 - 116); 0.5 mm (113).

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 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 153, 154. Ejaculatory apodeme + sac 153 Centrioncus decoronotus, paratype, Chania Falls 154 Teloglabrus sanorum, paratype, Drakensberg. Both drawings were processed based on original pencil drawings from Feijen (1983: figs 115, 126) and are drawn to the same scale. Scale bar: 0.2 mm.