Nilothauma hibaratertium Sasa, 1993

Niitsuma, Hiromi, 2016, Two species of Nilothauma Kieffer (Diptera, Chironomidae) from Japan, with description of a new species, Zootaxa 4079 (5), pp. 573-581 : 577-578

Nilothauma hibaratertium Sasa

( Figures 10–13 )

Nilothauma hibaratertia Sasa, 1993: 73 .

Tosayusurika simantofea Sasa, Suzuki & Sakai, 1998: 52 . Nilothauma sasai Adam & Saether, 1999: 61 . Syn. n.

Material examined. Holotype of Nilothauma hibaratertium : male (NSMT-I-Dip-4842), labelled, “ Nilothauma hibaratertia No. 223: 28”, light trap, JAPAN: Fukushima, Aizu, Bandai-Asahi National Park, Lake Hibara, 6.viii.1991. Paratypes of Nilothauma hibaratertium : 2 males (NSMT), labelled respectively, “No.223: 29, 30”, as holotype. Holotype of Tosayusurika simantofea : male (NSMT-I-Dip-5198), labelled, “No. 358: 45”, light trap, JAPAN: Kochi, Nakamura, Shimanto River, 26.iv.1998. Paratypes of Tosayusurika simantofea : 12 males (NSMT), labelled respectively, “No. 359: 51–54, 360: 43, 361: 1–7”, as holotype. Holotype of Nilothauma sasai : male with pupal and larval exuviae (SUM-IC-C0028), reared from larva, JAPAN: Fukushima, Iwaki, Obisa River, 15.viii.1988 (emerged 12.ix.1988). Non-types: male with pupal exuviae (SUM-IC-C0031), reared from pupa, JAPAN: Fukushima, Hirono, Asami River, 15.viii.1996 (emerged 29.viii.1996); male with pupal exuviae (SUM- IC-C0032), as previous except 15.viii.2001 (emerged 3.ix.2001); male (SUM-IC-C0033), as previous except 15.viii.2002 (emerged 24.viii.2002); 2 males with 1 pupal exuviae (SUM-IC-C0 0 34, C0035), as previous except 4.v.2005 (emerged 7 and 9.v.2005); male (SUM-IC-C0036), reared from pupa, JAPAN: Fukushima, Iwaki, Yaguki, 5.i.2013 (emerged 26.i.2013); male (MSU-IC-C0037), sweep net, JAPAN: Shizuoka, Shimizu, Yanbara River, 7.viii.2002.

Description. Male (n = 24). Total length 2.2–4.2, 2.9 (8) mm.

Coloration. Generally green. Wing without any marking. Foreleg pale yellow with base and sub-apex of femora, apices of tibia and tarsomere 1, and tarsomeres 2–5 dark brown.

Head. Temporals 8–14, 11. Frontal tubercles absent. AR 0.24–0.31, 0.26 (22). Palpomere 3 apically with 2 sensilla clavata, longest 23–28, 26 (18) µm long. Pm4/Pm3 1.3–1.6, 1.5 (21); Pm5/Pm4 1.2–1.4, 1.3 (21).

Thorax. Acrostichals 14–23, 17; dorsocentrals 8–16, 12 (23); prealars 3–5, 4. Scutellum with 2 setae.

Wing. Length 1.3–2.2, 1.9 (23) mm. VR 1.3–1.5, 1.4 (23). Brachiolum with 1 (8) seta; R with 9–20, 14 (8) setae; R1 with 7–16, 12 (8) setae; R4+5 with 2–19, 10 (8) setae.

Legs. Mid tarsomere 1 with 1–5, 3 (20) sensilla chaetica, distalmost located 0.14–0.31, 0.21 (20) from apex. LR1 1.37–1.54, 1.46 (16); LR2 0.54–0.62, 0.58 (23); LR3 0.52–0.58, 0.56 (23).

Hypopygium ( Figures 10, 11 ). Tergite IX with 2 dorsal projections and 9–17, 13 (10) posterior setae. Anterior projection ( Figures 12a–c ) 18–38, 28 (22) µm long, 0.75–1.2, 0.95 (22) times as long as broad, varying from simple lobe to two distinctly divided lobes, usually notched posteriorly, with about 20–50 plumose setae 40–59, 50 (22) µm long. Posterior projection 22–38, 30 (13) µm long, 0.73–1.2, 0.89 (11) times as long as basal width, basally microtrichiose, apically with 6–15, 9 (15) setae 12–20, 16 (17) µm long. Anal point 55–63, 59 (6) µm long, 1.8–1.9, 1.9 (6) times as long as broad, without microtrichia. Laterosternite IX with 2–7, 4 setae. Phallapodeme 50– 75, 64 (20) µm long. Sternapodeme bluntly triangular. Gonocoxite 88–125, 114 (22) µm long. Superior volsella ( Figure 13 ) pad-like, 37–50, 44 (22) µm long, microtrichiose with 1 long lateral and 5–8, 6 (21) short marginal setae on small tubercles; lateral seta 25–42, 32 (19) µm long. Median volsella 5–8, 7 (23) µm long, with 2–4, 3 (23) apical setae on small tubercles. Inferior volsella microtrichiose, with 7–10, 8 apically split setae. Gonostylus 105– 168, 149 (22) µm long, 5.3–5.9, 5.6 (6) times as long as broad at middle, parallel-sided for most of its length, with pointed apex; distal-median setae 6–10, 8 (22), uniserial, some split apically. HR 0.71–0.83, 0.77 (22).

Remarks. The male of Nilothauma sasai Adam & Saether, 1999 was separated from that of N. hibaratertium Sasa, 1993 by the simple anterior projection on tergite IX (see the key to male imagines, fig. 23F in Adam & Saether 1999). However, re-examination of the holotype male of N. sasai disclosed that the anterior projection is completely split into two lobes in conflict with the original description. I re-examined the following type series of N. hibaratertium and Tosayusurika simantofea Sasa, Suzuki & Sakai, 1998 , synonymized by Adam & Saether (1999): three male specimens of N. hibaratertium and 13 male specimens of Tosayusurika simantofea including each holotype. Consequently, it was revealed that the anterior projection in the paratype No. 359: 3 of T. simantofea is simple, not divided into two lobes. These show that the simple anterior projection is an individual variation in the species and N. sasai is a junior synonym of N. hibaratertium .

I examined 23 males of N. hibaratertium , including seven newly collected males. They showed great variation in the morphology of the anterior anal tergal projection: in four specimens (17%) the projection is completely divided into two lobes ( Figure 12a ), in 16 specimens (70%) the projection is notched to a varying degree ( Figure 12b ), and in three specimens (13%) the projection is simple ( Figure 12c ). The original description of N. sasai may be based on another loaned specimen, not returned to me.

Adam & Saether (1999: 71) regarded the Portuguese species illustrated under the name of N. brayi (Goetghebuer) by Cranston et al. (1989 fig. 10.41) as N. hibaratertium . However, the species may be different from N. hibaratertium because of the stout and triangular posterior projection on the male anal tergite. The posterior projection is relatively slender and club-shaped in N. hibaratertium .

Figures

FIGURES 10 – 13. Nilothauma hibaratertium Sasa, male. 10, hypopygium, ventral view (right) and dorsal view (left); 11, anal tergite with anal point, lateral view; 12 a – c, anterior projection on anal tergite, dorsal view, showing variation; 13, superior volsella, dorsal view.