Nilothauma aristatum, Qi, Xin, Tang, Hongqu & Wang, Xinhua, 2016

Qi, Xin, Tang, Hongqu & Wang, Xinhua, 2016, Notes on Nilothauma Kieffer from Oriental China, with descriptions of three new species (Diptera, Chironomidae), ZooKeys 574, pp. 143-159 : 145-149

Taxon classification Animalia Diptera Chironomidae

Nilothauma aristatum sp. n. Figs 12-17, 18-24

Type material.

Holotype: male with pupal exuviae (EJNU), CHINA: Anhui Province, Huangshan Nature Conservation Reserve, stream in Huang Mountain, 30°04.317'N, 118°09.320'E, Alt. 520 m, 4.v.2014, Tang HQ, light trap. Paratypes: 1 male (LTZU), CHINA: Zhejiang Province, Lin-An City, Tianmu Mountain, 16.vii.2012, Lin XL, hand net; male with larval and pupal exuviae (LTZU), reared by Lin XL, as previous; 3 pupal exuviae (EJNU), CHINA: Guangdong Province, Dongguan City, Yinping Nature Conservation Reserve, 22°53.772'N, 114°14.086'E, 17.iv.2012, Tang HQ, hand net.

Diagnosis.

The adult male of Nilothauma aristatum sp. n. can be distinguished from other known Nilothauma species by the anterior T IX projection with plumose setae; the anal point broadly lanceolate with microtrichia along the median ridge; the superior volsella slender with a lateral spur, and one lateral and 2−3 apical setae, without microtrichia. The pupa is characterized by the relatively short frontal setae (1.5−2.0 times as long as the major axis of basal ring); and the anal comb of abdominal segment VIII consisting of a main spur and a single accessory spine. The larva cannot be reliably separated from those of other species.

Etymology.

From Latin aristatus (aristate), referring to the male hypopygium with a lateral spur on the superior volsella.

Description.

Male imago (n = 2).

Total length 3.0−3.5 mm. Wing length 1.4−2.1 mm. Total length/wing length 1.7−2.2. Wing length/length of profemur 1.9−2.6.

Coloration. Entirely pale yellow. Wing without any marking (Fig. 12).

Head. AR 0.16−0.21. Temporals 6. Clypeus with 10−13 setae. Tentorium 145−170 μm long, 21−23 μm wide. Stipes 85−90 μm long, 8−10 μm wide. Lengths of palpomeres 1−5 (μm): 30−32, 30−40, 70−80, 130−140, 155−160. Palpomere 3 with 2 sensilla clavata, longest 10 μm long. Pm5/Pm3 1.9−2.3.

Thorax. Dorsocentrals 5−7, acrostichals 10−15, prealars 2−3, scutellars 1−2.

Wing. VR 1.4. Brachiolum with 1 seta, R with 13−15 setae, R1 with 11 setae, R4+5 with 3−4 setae.

Legs. Spur of foretibia 68−75 μm long including 30−43 μm long scale (Fig. 13). Spur of mid tibia 30−38 μm long (Fig. 14) including 16−25 μm long comb. Spurs of hind tibia 30−38 μm and 37−40 μm long, respectively (Fig. 15); comb 15−28 μm long. Width at apex of foretibia 40−50 μm, of mid tibia 45−50 μm, of hind tibia 43−54 μm. Lengths and proportions of legs in Table 3.

Hypopygium (Fig. 16). Tergite IX with 2 dorsal projections. Anterior projection completely divided into 2 oval lobes; each 35−37 μm long, 12−13 μm wide at middle, with 8−10 plumose setae 50−63 μm long. Posterior projection 10−12 μm long, 10−13 μm wide at base, 5−6 μm wide at apex, apically rounded, with 5 setae 13−20 μm long. Anal point very broadly lanceolate, 50−60 μm long, 18−20 μm at base, 25−27 μm at middle, with microtrichia along median ridge. Posterior margin of tergite IX (Fig. 17) with 9−11 setae. Laterosternite IX with 3 setae. Phallapodeme 37−40 μm long. Transverse sternapodeme without median elongation. Gonocoxite 114−120 μm long. Superior volsella 45−50 μm long, with lateral spur, and one lateral and 2−3 apical setae, without microtrichia. Median volsella 10−13 μm long, bearing 2 apical setae and microtrichia. Inferior volsella 78−90 μm long, curved dorsally, pointed apically, with microtrichia and 5 apically branched setae. Gonostylus 110−130 μm long, with 8 split median setae in distal 1/3. HR 1.02−0.92, HV 2.69−2.73.

Pupa (n = 4).

Total length 3.5−4.4 mm. Exuviae pale brown with anal comb on abdominal segment VIII yellowish brown.

Cephalothorax. Frontal seta short, 30−50 μm long (n = 2). Basal ring small, stoma-like, with major axis 20−25 μm long, minor axis 5−8 μm high. Frontal setae 1.8−2.0 times as long as major axis of basal ring. Thorax pebbled and rugose dorsally.

Abdomen (Fig. 18). Tergite I without spinulation; T II−VI extensively spinulated; T VII with anterior and posterior bands of spines; T VIII with anterolateral and median bands of spines; tergite T IX with median spinulation in female (Fig. 21), but without any spinulation in male. S I−II without spinulation; S III−IV with anterior spinulation; sternite IV with weak anterolateral spinulation; S V with weak anterolateral and caudolateral spinulation; S VI−VIII with anterolateral and median spinulation, occasionally anterolateral spinulation merged to median in S VIII (Fig. 20). T II with row of 70−78 caudal hooklets with posterior groups of points behind each end. Conjunctives III/IV and IV/V with rows of spinules. Pedes spurii B weakly developed on segment II. Anal comb of segment VIII (Fig. 19) composed of main spur 20−30 μm long and single accessory spine 7.5−17.5 μm long. 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 μm long, 2.4−2.6 times as long as broad, with 35−48 lateral setae, dorsal seta located near distal 1/3.

Larva (n = 1).

Total length 5 mm. Head capsule about 300 μm long, about 260 μm wide.

Coloration. Red color in fresh specimens, head pale yellow. Mentum and postoccipital margin brown.

Antenna (Fig. 22). Lengths of antennal segments 1-6 (μm): 28, 10, 4, 13, 4, 4. AR 0.8. Basal segment with ring organ situated in distal 1/6; antennal blade 25 μm long, extending to apex of segment 4; segment 6 hair-like, almost as long as segment 5.

Mandible (Fig. 23). Total length 85 μm. Apical tooth 40 μm long; 4 inner teeth small, arising from common base. Seta subdentalis 30 μm long, reaching middle of apical tooth.

Mentum (Fig. 24). Width 55 μm. Two pale median teeth and 7 pairs of gradually decreasing lateral teeth present. Ventromental plate 65 μm wide.

Female imago. Unknown.

Remarks.

The male is similar to that of Oriental species Nilothauma acre Adam & Sæther, 1999 in having the wing unmarked, the anterior T IX projection with plumose setae, the anal point lanceolate, and the superior volsella slender with a lateral spur and one lateral and two three apical setae. It differs from it as the anal point bears microtrichia along the median ridge, the superior volsella is relatively long compared to the median volsella (length ratio, Svo/Mvo> 4.0) and the inferior volsella has simple setae only. In Nilothauma acre , the anal point is bare, length of Svo/Mvo is around 2.0 and the inferior volsella has apically split setae.

The pupa of Nilothauma aristatum sp. n. will key to " Nilothauma sp. Australia" in Adam and Sæther (1999), but may be separable by the relatively short frontal setae. The ratio of the length of the frontal seta to the length of the major axis of basal ring is 1.8−2.0 in Nilothauma aristatum sp. n., but 4.6−6.5 in the latter. The larva of Nilothauma aristatum sp. n. somewhat resembles that of Nilothauma japonicum Niitsuma, 1985, but it remains uncertain because of a paucity of data.

Distribution.

Oriental China (Anhui, Guangdong and Zhejiang Provinces).

Biological note.

The larva and pupa of Nilothauma aristatum sp. n. are found in first-, or second-order streams. The water is relatively clean and cold (water temperature 15°C−20°C, pH 7.80−7.88, DO% 90.6−93.4, DO 8.09−9.36 mg/l, and conductivity 25−34 μs /cm). The co-existing dominant species of chironomids are Eukiefferiella spp., Rheotanytarsus spp., Rheocricotopus spp., and Parametriocnemus spp. Some steno-thermic species, such as Heleniella sp. and Pagastia sp., are frequently observed in the pupal exuviae samples.