Centrioncus jacobae 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 jacobae Feijen

Figs 7 , 127-131 , 132-135 , 136-138

Centrioncus jacobae Feijen, 1983: 87; Feijen and Feijen 2021: figs 16, 44, 46, 47.

Type material.

Malawi, holotype ♂, Limbe [Blantyre], Mount Soche [15°50'21"S, 35°1'10"E], 1300-1400 m, 22.x.1972, H.R. & J.J. Feijen (RMNH). Paratypes: 3 ♀, 2 ♂, same data as holotype; 7 ♀, 4 ♂, Limbe, Mount Soche, 1300-1400 m, 27.ii.1972; 2 ♀, 3 ♂, Limbe, Mount Soche, 1300-1400 m, 19.iii.1972, H.R. Feijen; 1 ♀, Mount Chiradzulu [Chiradzulu district, near Limbe, 15°41'47.11"S, 35°10'34.20"E], 1300-1350 m, 7.v.1972, H.R. Feijen; 1 ♀, 9 ♂, Limbe, Mount Ndirande [15°45'28"S, 35°3'19"E], 1400 m, 16.xi.1974, H.R. & J.J. Feijen. Next to the holotype, 14 ♀ and 18 ♂ paratypes were traced in the RMNH collections. This is slightly different from the 15 ♀ and 15 ♂ paratypes mentioned by Feijen (1983).

Additional material studied.

Malawi: 3 ♀, Limbe , Mount Ndirande [15°45'28"S, 35°3'19"E], 1400 m, 23.iv.1972, H.R. & J.J. Feijen (RMNH) ; 4 ♀, 5 ♂, Limbe , Mount Soche, [15°50'21"S, 35°1'10"E], 1300-1400 m, 7.viii.1974, H.R. Feijen (RMNH) ; 1 ♂, Limbe , Mount Soche, 1300-1400 m, 1972-1975, H.R. Feijen (RMNH) ; 3 ♀, 5 ♂, Limbe , Mount Soche, 1300-1400 m, 19.iii.1972, H.R. Feijen ; 3 ♀, 1 ♂, Limbe , Mount Soche, 1300-1400 m, 7.viii.1974, H.R. Feijen ; 5 ♀, 5 ♂, Limbe , Mount Soche, 1300-1400 m, 7.i.1973, H.R. Feijen ; 3 ♂, Limbe , Mount Ndirande, 1400 m, 10.vii.1975, H.R. & J.J. Feijen. Including the type series, a total of 32 ♀ and 39 ♂ were collected from 1972-1975. This additional material was not included in Feijen (1983) because the author was working in Mozambique and later Zanzibar and did not transport the whole series to those countries.

Diagnosis.

Centrioncus jacobae can be recognised by the mesally slightly depressed pruinose frons with glossy areas (Fig. 128 ); glossy collar; thinly pruinose scutum with typical configuration of blackish brown and chestnut-brown (Figs 126 , 127 ), brown humeral calli and laterally large brown presutural and postsutural areas; scutellum brown, pale brown scutellar spines; pleura chestnut-brown, blackish area around anterior spiracle, blackish posterior third; scutellar spine/scutellum ratio: 0.78; apical seta/scutellar spine ratio: 1.11; pale, strongly incrassate fore femur (l/w ratio: 2.78) with ~ 33.3 tubercles, inner side with broad brown stripe on distal three-fifths (Fig. 130 ); large central wing spot (Fig. 7 ), covering more than basal third of cell r4+5, extending into cells br and bm+dm; tergites blackish brown, two striking, large rectangular pale spots in the posterolateral corners of tergite 2 (Fig. 135 ); sternite 4 rectangular, sternite 5 slightly broadening posteriorly, sternites 4 and 5 both with anterior pair of small heavily sclerotised spots (Fig. 132 ); sternite 6 trapezoidal, 1.5 × as broad as sternites 1-5; female 7th spiracle in tergite; anterior sclerite of female sternite 7 with w/l ratio: ~ 2.6; posterior sclerite of female sternite 7 smoothly curved, slender, semi-circular U-shaped (Fig. 133 ); female cercus rather elongate, l/w ratio: 3.2; subanal plate pentagonal, lateral and apical sides straight; spermathecae round, smooth, with dimple, some dispersed tiny tubercles; common base of outer and median arm of surstylus short, broad; outer arm rounded, elongate, basally strongly constricted, largest width 2.7 × basal width, apically with ~ 7.6 tubercles (Fig. 138 ); median arm longer than outer arm, club-shaped, rather broad, apically with ~ 4.0 spinous setae; outer and median arm almost fully clothed in microtrichia on outer side; inner arm much shorter than median arm, apically rounded, halfway with a rounded apophysis (Fig. 138 ); subepandrial clasper triangular, basal third constricted, medial apical corner pointed, extended lateral corner rounded (Fig. 138 ); male cercus with a long lateral, parallel-sided extension on distal quarter.

Supplementary description.

Biometrical data are given for the remeasured series. Additional morphological data and illustrations are also presented.

Measurements. Feijen (1983) measured 20 ♀and 26 ♂ and gave as results: body length ♀ 5.61 mm ± SE 0.07 (range 5.2-6.2) and ♂ 5.28 mm ± 0.04 (4.8-5.7), head width ♀ 1.19 mm ± 0.01 (1.08-1.28) and ♂ 1.15 mm ± 0.01 (1.00-1.21), wing length ♀5.02 mm ± 0.06 (4.6-5.5) and ♂ 4.70 mm ± 0.05 (4.4-5.1), scutellar spine length ♀ 0.289 mm ± 0.006 (0.25-0.33) and ♂ 0.273 mm ± 0.004 (0.23-0.31). Of the original type series, 10 ♀ and 10 ♂ were remeasured in detail. In Table 5 , the new measurements and other quantitative characters are presented. 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. Body length and various other measurements are slightly larger for the females.

The original measurements of the type series do not agree well with the measurements now recorded. The measurements now found for ♀ and ♂ combined are: body length 4.97 mm ± 0.06 (range 4.58-5.43, n = 20), head width 1.11 mm ± 0.01 (range 1.04-1.21, n = 20), wing length 4.28 mm ± 0.05 (range 3.78-4.64, n = 20), scutellar spine length 0.27 mm ± 0.00 (range 0.24-0.29, n = 20). This means that the present measurements for body length and wing length are ~ 10% less, while the measurements for head width and scutellar spine are ~ 5% less. The specimens of the type series were measured in Malawi while in fresh condition. This could only affect the body length measurements to a small extent but not the other measurements. The persistent differences are probably due to calibration errors. The new measurements now indicate C. jacobae as a species is clearly smaller than the other Centrioncus species for which large series could be measured. (Tables 6 , 7 ).

In connection with ecological research in Malawi from 1971 to 1975, the weight of fresh flies was regularly determined. The weight of some C. jacobae flies was also determined. In August (in the non-reproductive phase) seven females weighed on average 4.2 mg, while six males weighed on average 3.4 mg.

Colour. In optimal conditions, this species presents a colourful pattern of blackish brown and chestnut brown on the thorax as described by Feijen (1983) and now illustrated (Figs 126 , 127 ).

Head. Colour pattern of anterior and posterior sides of head shown in Figs 126 , 128 ; length of outer vertical seta 0.33 mm ± 0.01 (n = 19), length of fronto-orbital seta 0.22 mm ± 0.01 (n = 18).

Thorax. Basiliform prosternum brown, slender, triangular and anteriorly acuminate (Fig. 129 ); scutellar spine/scutellum ratio: 0.78 ± 0.01 (n = 19, Tables 5 , 7 ); scutellar spine/body length ratio: 0.054 ± 0.000 (n = 20); apical seta/scutellar spine ratio: 1.11 ± 0.02 (n = 17), Feijen (1983) described apical seta as being "as long as spine", but seta is now shown to be slightly longer than spine; scutellar length/scutellar width (at base) ratio: 0.68.

Wing. Pale brownish with distinct, large central wing spot, covering more than basal third of cell r4+5 (just past crossvein dm-m), slightly extending into apex of cell br and extending into anterior section of cell bm+dm between crossveins (Fig. 7 ); distinct infuscation along crossvein dm-m and along vein M4 between cell cua and crossvein dm-m; vein CuA+CuP from vein CuP onward extending under angle of 30° to wing margin in almost straight line (very sightly curving downward); vein M4 continuing distal of crossvein dm-m in almost straight line to wing margin; cell cua triangular (Fig. 7 ).

Legs. Femur 1 (Figs 126 , 130 ) strongly incrassate, l/w ratio: 2.78 ± 0.02 (n = 18, Tables 5 , 7 ); two rows of spinous setae on distal two-thirds of femur 1 with 8.9 ± 0.1 setae (n = 39; Tables 5 , 7 ), inner row with 4.9 ± 0.1 setae and outer row with 4.0 ± 0.1 setae; two rows of tubercles on distal three-quarters of femur 1 with 33.3 ± 0.3 tubercles (n = 36), inner row with 15.4 ± 0.2 tubercles and outer row with 17.8 ± 0.2 tubercles; femur 1 on inner side with broad brown stripe on distal three-fifths (Fig. 130 ); femur 3 (Fig. 131 ) distally with 6.0 ± 0.2 (n = 37), tubercles in single row but one specimen with one tubercle placed in second row. Results lead to setal formula: 4.0, 4.9, 17.8, 15.4, 6.0 which agrees well with formula of the type-series as given by Feijen (1983): 4.0, 4.7, 16.9, 15.4, 5.6.

Preabdomen. Tergites blackish brown (Figs 135 , 136 ), almost glossy, but with some pruinosity, especially at posterior margins of tergites 2 and 3 (Fig. 136 ); tergite 2 with two striking, large, pale brown rectangular areas in posterolateral corners (Fig. 135 ); smaller pale brown spots in posterolateral corners of tergites 3, 4, and 5; sternites 1 and 2 and anterior half of sternite 3 dark brown, posterior half of sternite 3 and sternites 4-6 yellowish brown (Fig. 134 ); sternite 1 glossy but laterally with some pruinosity; sternite 2 glossy with pruinose posterior margin; sternites 3-6 pruinose (Figs 132 , 134 ); membranous ventral areas with large dark lateral spots (Fig. 134 ); sternite 1 somewhat rectangular, with concave anterior and posterior sides (Fig. 132 ); intersternite 1-2 dark, laterally acuminate, with thin lateral connections to main sternite 2; sternite 3 rectangular; sternite 4 rectangular, sternite 5 slightly broadening posteriorly, both sternites with pair of tiny heavily sclerotised spots, and with slightly more sclerotised areas posterior to spots (Fig. 132 ); sternite 6 ~ 1.5 × as broad as sternites 1-5, with convex lateral sides and somewhat broadening posteriorly.

Female postabdomen. Tergite 7 brown anteriorly and yellowish brown posteriorly (Fig. 135 ); anterior sclerite of sternite 7 rectangular, w/l ratio: ~ 2.6 (Figs 133 , 134 , Table 8 ), dark brown and glossy on anterior half, more yellowish brown and pruinose on posterior half; posterior sclerite of sternite 7 slender, rounded, U-shaped (Fig. 133 ), clothed in microtrichia and with four setulae at posterior apices; cercus rather elongate, l/w ratio: 3.2 (Table 8 ); 7th spiracle in tergite (Fig. 133 ).

Male postabdomen. Lateral side of male postabdomen shown in Fig. 136 ; epandrium, surstylus and subepandrial clasper presented in Figs 137 , 138 ; common base of outer and median arm of surstylus short, broad; outer arm rounded, elongate, basally strongly constricted, largest width 2.7 × basal width, apically with 7.6 (range 7-9) tubercles (Figs 137 , 138 ); median arm long (longer than outer arm), club-shaped, rather broad, apically with 4.0 (range 3-5) stout spinous setae; outer and median arm almost fully clothed in microtrichia on outer side; inner arm much shorter than median arm, apically rounded, halfway with a rounded apophysis (Fig. 138 ); subepandrial clasper triangular, basal third constricted, medial-apical corner pointed, extended lateral corner rounded (Figs 137 , 138 ); cercus with broad lateral extension on distal third, length/greatest width ratio: 1.4 (Table 8 ); ejaculatory apodeme + sac very large, 11-14% of body length (Table 9 ).

Distribution and habitat.

This species occurs at altitudes between 1300 and 1400 m in rain forests on the mountains around Blantyre and Limbe in Malawi. The rain forest at Mount Ndirande is gone, but patches on Mount Soche remain. The largest patches of rain forest remain on Mount Chiradzulu. However, this latter remark is quite relative when Loveridge’s (1954) observations about the Chiradzulu forest are considered: "Unfortunately the forest was but a pitiful remnant of its former self, few of its trees exceeding thirty feet in height and even these patches of secondary growth were separated by bracken which had swept up from below" and "This deforestation has resulted in the drying up of many of the streams during much of the year". The strong discontinuity of the habitat of Afromontane Forest Flies will obviously be reinforced by the ongoing deforestation.

In the period 1971-1975, extensive collecting of Diopsidae was carried out in Malawi. Regular sampling took place on other mountains in Malawi, like the Nyika Plateau, Ntchisi Mountain, Dedza Mountain, Zomba Plateau and Mount Mulanje. However, Centrioncus were never encountered on these other mountains.

Remarks.

Feijen (1983) remarked that Centrioncus jacobae was every now and then collected together with other diopsids, especially Diopsis phlogodes Hendel. However, this was a misidentification of a species of the D. cruciata species-group. Diopsis phlogodes is a junior synonym of the rice stem-borer D. longicornis Macquart (see Feijen 1985).

Figures

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 126 - 131. Centrioncus jacobae, paratypes 126 Mt Ndirande 127 - 131 Mt Soche 126 ♂, habitus, lateral view 127 ♀, thorax, dorsal view 128 ♂, head, anterolateral view 129 ♀, basiliform prosternum, ventral view 130 ♀, fore femur, inner view 131 ♂, hind femur, inner view. Scale bars: 0.5 mm (126 - 128); 0.2 mm (129 - 131).

Figures 132 - 135. Centrioncus jacobae, ♀, paratype, Mt Soche 132 sternites 1 - 6, ventral view 133 sternite 7, ventral view 134 abdomen, ventral view 135 abdomen, dorsal view. Scale bars: 0.5 mm (132, 134, 135); 0.2 mm (133).

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).