Nilothauma niidaense, Niitsuma, 2016

Niitsuma, Hiromi, 2016, Two species of Nilothauma Kieffer (Diptera, Chironomidae) from Japan, with description of a new species, Zootaxa 4079 (5), pp. 573-581 : 574-577

Nilothauma niidaense n. sp.

( Figures 1–9 )

Type material. Holotype male with pupal exuviae (SUM-IC-C0006), reared from pupa, JAPAN: Fukushima, Iwaki, Yaguki, headstream of Niida River , 27.iii.2013 (emerged 5.iv.2013) . Paratypes: 2 males with 1 pupal exuviae (SUM-IC-C0001, C0002), as holotype except 10.viii.1997 (emerged 21 and 25.viii.1997); male (SUM-IC- C0004), 2 females with 1 pupal exuviae (SUM-IC-C0003, C0005), as holotype except 5.i.2013 (emerged 12– 16.i.2013); 3 males with 1 pupal exuviae (SUM-IC-C0007, C0 0 0 8, C0010), 3 females with 3 pupal exuviae (SUM- IC-C0009, C0011, C0012), as holotype except 27.iii.2013 (emerged 17–25.iii.2013); male (SUM-IC-C0013), as holotype except 5.v.2013 (emerged 23.v.2013); 11 males with 6 pupal exuviae (SUM-IC-C0016–C0018, C0020– C0027), 3 females with 3 pupal exuviae (SUM-IC-C0014, C0 0 15, C0019), as holotype except 10.v.2014 (emerged 17–23.v.2014).

Derivatio nominis. From the type locality, Niida River in Fukushima Prefecture, Japan.

Description. Male (n = 19). Total length 2.4–3.4, 2.9 mm.

Coloration. Generally green. Thorax with four yellowish vittae on scutum and horizontal blackish band on annepisternum. Wing without any marking. Foreleg pale yellow with both ends of femora, apex of tibia, apical third to half of tarsomere 1, and tarsomeres 2–5 dark brown. Mid and hind legs entirely pale yellow. Abdomen olive green with dark tergites VI–IX.

Head. Temporals 9–11, 10 (17), uniserial. Frontal tubercles minute, 3–5, 4 µm long. Antenna with terminal flagellomere 110–165, 139 µm long and shorter than preceding 3 segments together; AR 0.15–0.21, 0.18. Clypeus rounded with 10–21, 17 setae. Lengths of palpomeres 1–5 (µm): 30–40, 36 (18); 30–43, 36 (18); 60–88, 76 (18); 125–163, 144 (18); 153–203, 173 (18). Palpomere 3 apically with 2 sensilla clavata, longest 18–25, 21 µm long. Pm4/Pm3 1.7–2.1, 1.9 (18); Pm5/Pm4 1.1–1.3, 1.2 (18).

Thorax. Antepronotal lobe much reduced; antepronotals absent. Acrostichals 11–17, 14, biserial; dorsocentrals 7–11, 9, uniserial; prealars 2–3, 3. Scutellum with 2 setae.

Wing ( Figure 1 ). Length 1.5–2.2, 1.8 mm. VR 1.4–1.5, 1.5. Brachiolum with 1 seta; R with 10–16, 14 setae; R1 with 9–16, 13 setae; R4+5 with 1–17, 7 setae.

Legs. Spur of foretibia 55–70, 62 µm long including 20–32, 27 µm long scale. Spur of mid tibia 37–45, 40 µm long including 22–30, 26 µm long comb. Spurs of hind tibia 40–50, 45 µm and 35–43, 38 µm long, respectively, and each comb 25–33, 28 µm long. Mid tarsomere 1 with 1–3, 1 (18) sensilla chaetica, distalmost located 0.29– 0.41, 0.34 (18) from apex. Lengths and proportions of leg segments as in Table 1.

Hypopygium ( Figures 2, 3 ). Tergite IX with 13–20, 17 (18) posterior setae, sitting to each side of anal point and 2 dorsal projections. Anterior projection 30–38, 34 (18) µm long, 1.1–1.5, 1.3 (13) times as long as broad, with about 30–40 plumose setae 43–72, 62 (18) µm long and tending to be divided into 2 caudolateral groups; occasionally with small median notch in posterior border ( Figure 4 ). Posterior projection club-shaped, 25–38, 31 (10) µm long, 2.0–3.0, 2.6 (10) times as long as basal width, bare except swollen apex with brush of 6–12, 8 (18) setae 12–20, 16 (18) µm long. Anal point 42–65, 54 (16) µm long, 1.4–1.8, 1.6 (11) times as long as broad, without microtrichia. Laterosternite IX with 2–4, 3 setae. Phallapodeme 37–64, 47 (13) µm long. Sternapodeme medially thickened, with or without small median elongation. Gonocoxite 97–113, 105 (12) µm long. Superior volsella ( Figures 5a, b ) slender, parallel-sided, 37–50, 45 (11) µm long, 5–8, 6 (11) µm wide at middle, with subapical spur, 1–2 conspicuous subapical setae and apical brush of 4–6 (5) setae; subapical spur 8–15, 11 (18) µm long, subapical setae 23–33, 28 (9) µm long. Median volsella 8–10, 10 (15) µm long, 1.5–2.0 times as long as broad, with microtrichia and 2–3, 3 apical setae. Superior volsella 3.7–5.0, 4.5 (11) times as long as median volsella. Inferior volsella with microtrichia and 5–7, 5 (18) apically split setae. Gonostylus 1 30–150, 137 (11) µm long, 5.3–6.0, 5.8 (11) times as long as broad at middle, gently curved inwards, pointed apically, with row of 6–9, 7 (12) distalmedian setae, some split apically. HR 0.74–0.82, 0.77 (11).

Female (n = 8). Total length 2.4–2.5 (2) mm.

Coloration. Similar to male.

Head. Temporals 9–11, 10 (7). Frontal tubercles 3–5, 4 µm long. Lengths of antennal flagellomeres 1–6 (µm): 68–75, 70; 60–65, 63; 68–75, 72; 75–88, 78; 65–78, 71; 113–135, 119. AR 0.32–0.38, 0.34. Clypeus with 16–24, 20 setae. Lengths of palpomeres 1–5 (µm): 35–45, 39; 38–45, 40; 83–105, 89; 163–198, 174; 183–228, 202. Palpomere 3 apically with 2 sensilla clavata, longest 20–28, 24 µm long. Pm4/Pm3 1.9–2.1, 2.0; Pm5/Pm4 1.1–1.2, 1.2.

Thorax. Acrostichals 15–21, 18; dorsocentrals 10–14, 12; prealars 3–4, 3; scutellars 2.

Wing. Length 2.0–2.3, 2.1 mm. VR 1.4–1.5, 1.5. Brachiolum with 1–2, 1 seta; R with 11–18, 16 setae; R1 with 16–30, 23 setae; R4+5 with 27–45, 35 setae.

Legs. Spur of foretibia 60–70, 66 µm long including 25–35, 29 µm long scale. Spur of mid tibia 43–50, 45 µm long including 25–28, 26 µm long comb. Spurs of hind tibia 48–60, 51 µm and 40–45, 43 µm long, respectively; comb 28–33, 30 µm long. Mid tarsomere 1 with 4–9, 6 sensilla chaetica, distalmost located 0.12–0.18, 0.15 from apex. Lengths and proportions of leg segments as in Table 2.

Genitalia ( Figure 6 ). Sternite VIII with 46–56, 50 setae on each side. Gonocoxapodeme VIII straight. Gonapophysis VIII divided into broad dorsomesal lobe and vestigial ventrolateral lobe. Gonocoxite IX with 2–5, 4 setae. Apodeme lobe weak. Segment X without setae. Coxosternapodeme nearly straight. Notum128–155, 137 µm long, 2.1–2.6, 2.4 times as long as ramus. Labium without microtrichia. Seminal capsule oval, 55–63, 59 (3) µm long, 45–48, 47 (3) wide, with cylindrical neck. Postgenital plate triangular. Cercus 75–93, 83µm long, 1.3–1.6, 1.5 times as long as ramus.

Pupa (n = 16). Total length 3.3–4.6, 3.9 mm (15).

Coloratio n. Exuviae pale brown.

Cephalothorax. Frontal seta 33–50, 39 µm long. Frontal apotome smooth. Scutum pebbled and rugulose. Thoracic horn ( Figure 7 ) consisting of 4 slender filaments, 1 or 2 of them bifid. Diameter of basal ring 17–25, 22 µm (15).

Abdomen ( Figure 8 ). Tergite I without shagreen; tergites II–VII each with more or less extensive and uniform shagreen; tergite VIII with anterolateral and median shagreen; tergite IX with median shagreen in female, without any shagreen in male. Tergite II with row of 50–81, 71 (15) caudal hooklets. Conjunctives III/IV and IV/V each with 4–6, 5 (13) rows of spinules. Pedes spurii B weakly developed on segment II. Pedes spurii A absent. Anal comb ( Figures 9a, b ) on segment VIII consisting of single spur with or without marginal accessory spine. Segment I without L-setae; segments II–III each with 3 L-setae on each side; segment IV with 2 L-setae and 1 LS-seta on each side; segments V–VIII each with 4 LS-setae on each side. Anal lobe 200–240, 217 (12) µm long, 1.7–1.9, 1.8 (8) times as long as broad, with dorsal seta located 0.19–0.30, 0.24 (14) from apex, and fringe of 33–58, 47 (15) lateral setae; male genital sac 1.3–1.4, 1.4 (6) times as long as lobe.

Larva. Unknown.

Remarks. Nilothauma niidaense n. sp. belongs to the N. brayi species group as the wing lacks dark markings and the anal tergite has two dorsal projections (see Adam & Saether 1999: 38). The male of the species is similar to That of Oriental species N. acre Adam & Saether, 1999 in the anal tergite with about 30–40 plumose setae on the anterior projection, the broad anal point, and the superior volsella with a pointed spur and a laterally directed seta, but differs in the slender, club-shaped posterior projection on the anal tergite, and the superior volsella having an apical brush of 4–6 setae. In N. acre , the posterior projection is broad basally and triangular, and the superior volsella is armed with only 1 or 2 apical setae.

The pupa resembles that of N. sasai Adam & Saether, 1999 , treated here as a junior synonym of N. hibaratertium Sasa , in the following features: thoracic horn with 5 branches, pedes spurii B present, abdominal tergite II with 50 or more caudal hooklets, anal comb on abdominal segment VIII consisting of a single spur with or without a marginal accessory spine, and abdominal tergite VIII with distinct anterior shagreen. A re-examination of the holotype pupal exuviae of N. sasai deposited in SUM, however, revealed that both the pupae are separable by the feature of abdominal shagreen. Anterior shagreen patches on abdominal tergites III–VI are distinct because of larger spinules in N. sasai , but indistinct in N. niidaense sp. n.

Figures

FIGURES 1 – 9. Nilothauma niidaense n. sp., male (1 – 5), female (6) and pupa (7 – 9). 1, Wing; 2, hypopygium, ventral view (right) and dorsal view (left); 3, anal tergite with anal point, lateral view; 4, anterior projection on anal tergite, dorsal view; 5 a, b, superior volsella and median volsella, dorsal view, showing variation of superior volsella; 6, genitalia, ventral view; 7, thoracic horn; 8, abdomen, dorsal view, left lateral and dorsal setae omitted; 9 a, b, anal comb of abdominal segment VIII, showing variation of spur.