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Research Article
Taxonomic study on the genus Stenochironomus Kieffer from the Baishanzu Nature Reserve, China (Diptera, Chironomidae)
expand article infoChao Song‡, Bin-Qing Zhu§, Joel Moubayed-Breil|, Teng Lei‡, Xin Qi‡
‡ Taizhou University, Taizhou, China
§ Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment, Nanjing, China
| Freshwater & Marine biology, Montpellier, France

Corresponding author: Xin Qi ( qixin0612@163.com )

Academic editor: Fabio Laurindo da Silva
© 2022 Chao Song, Bin-Qing Zhu, Joel Moubayed-Breil, Teng Lei, Xin Qi.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Song C, Zhu B-Q, Moubayed-Breil J, Lei T, Qi X (2022) Taxonomic study on the genus Stenochironomus Kieffer from the Baishanzu Nature Reserve, China (Diptera, Chironomidae). ZooKeys 1104: 93-113. https://doi.org/10.3897/zookeys.1104.81403
ZooBank: urn:lsid:zoobank.org:pub:E19A9296-55A8-4640-8DC0-0F9E34357F1E
Open Access

Abstract

During the summer of July to September 2020, a biodiversity survey on Chironomidae of Baishanzu Nature Reserve, China was made. In total, five Stenochironomus taxa/species were discovered, of which two belong to undescribed species and one (S. okialbus Sasa, 1990) is reported for the first time from China. The male adults of two new species are described and illustrated. Stenochironomus annulus Song & Qi sp. nov. is distinguished in having a wing with two dark spots restricted to the fork area of FCu and RM, the mid- and hind-femur each with a brown annulus, and the inferior volsella with two setae and one strong terminal spine. Stenochironomus baishanzuensis Song & Qi sp. nov. is distinguished by a combination of characters: a single dark spot on the middle part of the wing, fore legs brown to dark brown except for the basal 3/4 of femur, and the inferior volsella with four long setae and one stout terminal spine. The neighbour-joining tree based on public COI barcodes formed distinct clades with clear support for the new species. An updated key to known male adults of Stenochironomus from China is also provided.

Keywords

Chironominae, DNA barcode, new species, non-biting midge, Stenochironomus, taxonomy

Introduction

The genus Stenochironomus Kieffer, 1919 has a cosmopolitan distribution in all zoogeographical regions except for Antarctica (Cranston et al. 1989). The larvae are known as miners and occur in different habitats such as dead wood, dead leaves, and floating leaves of lotuses, Nelumbo (Borkent, 1984). Male adults are characterized by a combination of characters as documented by Borkent (1984) and Townes (1945): different color patterns of the thorax and legs; short to elongate, variably sausage-shaped superior volsella with several bristles; and long narrow curved inferior volsella with few apical bristles and terminal spines. Stenochironomus is composed of two subgenera, Stenochironomus s. str. and Petalopholeus, which cannot be differentiated on imaginal morphology.

Data on the taxonomy, keys, and geographical distributions for Stenochironomus show that there are 110 known valid species recorded worldwide, of which 14 species are reported from China (Qi et al. 2008a, b, 2011, 2015; Dantas et al. 2016; Parise and Pinho 2016; Zhang et al. 2016; Amora et al. 2018; Lin et al. 2021).

DNA barcoding employs sequence diversity in short, standardized, gene regions and has become an important tool for species identification and cryptic species discovery (Hebert et al. 2003). Chironomid researchers also confirmed the effectiveness of a DNA barcode reference library in the discovery of new species using the 658-bp fragment of the mitochondrial gene cytochrome c oxidase I (COI) (Kodama et al. 2018; Lin et al. 2020, Qi et al. 2020; Song et al. 2020).

Baishanzu is a nature reserve, spanning the south Zhejiang and north Fujian provinces of eastern China. It belongs to the tropical to warm temperate transitional zone and is a biodiversity hot spot in Asia with the dominant types of vegetation being evergreen broad-leaved forests and mixed coniferous and broad-leaved forests (Peng et al. 2012). During seasonal surveys of the nature reserve, five Stenochironomus taxa/species were discovered, of which two belong to undescribed species and one, S. okialbus Sasa, 1990, is reported for the first time from China. In addition, DNA barcodes of the new species were analyzed and clearly supported them as new species. An updated key to male adults of known Stenochironomus from China is also provided.

Materials and methods

Morphological study

The examined material was collected using light traps; the specimens were preserved in 75% ethanol at 4 °C in a refrigerator before final slide mounting. Specimens were side-mounted in Euparal after genomic extraction following the procedure described by Sæther (1969). Morphological terminology follows that of Sæther (1980). The photographs of the habitus of each specimen were obtained with a DV500 5MP Digital Camera attached to a stereo microscope (Chongqing Optec SZ680). The photographs of the body parts were obtained using a Leica DMLS compound microscope. Photograph post-processing was done in Adobe Photoshop and Illustrator version 8 (Adobe Inc., California, USA).

The type material including holotype and paratypes of the two new described species are deposited in the collection of the College of Life Sciences, Taizhou University, Taizhou, China (TZU).

Abbreviations used are as follows

AR antennal ratio, length of the 13th / length of flagellomeres 1–12;

BV length of (femur + tibia + ta1) / length of (ta2 + ta3 + ta4 + ta5);

Cu cubitus;

Dc dorsocentrals;

Fe femur;

HR hypopygium ratio, length of gonocoxite / length of gonostylus;

HV hypopygium value, total length / 10* length of gonostylus;

IV inner verticals;

LR leg ratio; Length of ta1 / length of tibia;

M media;

MCu cross-vein between media and cubitus;

P1, P2, P3 Fore leg, mid leg, hind leg;

R radius;

RM cross-vein between radius and media;

Tatarsomere;

Ti tibia;

VR venarum ratio, length of Cu / length of M.

Molecular study

Tissues for total genomic DNA extraction were removed from the thorax and head of the adults. The genomic extraction procedure followed Frohlich et al. (1999). The standard barcode region of the 5’ portion of the mitochondrial gene cytochrome c oxidase I (COI-5P) was amplified using the universal primers LCO1490 and HCO2198 (Folmer et al. 1994); PCR amplifications followed Song et al. (2018). PCR products were electrophoresed in 1.0% agarose gel, purified, and sequenced using an ABI 3730XL capillary sequencer (Beijing Genomics Institute Co., Ltd., Hangzhou, China). Raw sequences were edited in BioEdit 7.2.5 (Hall 1999).

Public Stenochironomus sequences were searched in GenBank, and 32 sequences were returned, of which eleven sequence were mitochondrion complete genomes. We extracted COI-5P barcode segments from those genomes.

The pairwise distances were calculated using the Kimura 2-Parameter (K2P) substitution model in MEGA 7 (Kumar et al. 2016). The neighbour-joining tree was constructed using the K2P substitution model, and 1000 bootstrap replicates and the “complete deletion” option for missing data were utilized. Automatic Barcode Gap Discovery (ABGD) analysis was implemented on the website (wwwabi.snv.jussieu.fr/public/ abgd/abgdweb.html, Puillandre et al. 2012), with K2P model. Sequences, trace-files, and metadata of the new species were uploaded to the Barcode of Life Data Systems (BOLD) (Ratnasingham and Hebert 2013).

Results and discussion

Barcode analysis

All 44 public COI-5P DNA barcodes comprising GenBank accessions and sequences from this study (Table 1) representing 12 species within Stenochironomus were used to construct the neighbour-joining tree. The twelve species formed 16 distinct genetic clades; two clades separately presented for the new species Stenochironomus annulus sp. nov., and S. baishanzuensis sp. nov. (Fig. 1). Stenochironomus annulus sp. nov. can be distinguished from other species by more than 11.2%, and S. baishanzuensis sp. nov. by more than 14.0% (Table 2). In the barcoded Stenochironomus species, there is a gap between 4–6% (Fig. 2), which may be used for the delimitation of Stenochironomus species. The thresholds for different Chironomidae groups are not always the same; for example, Lin et al. (2015) found a gap of 4–5% for Tanytarsus and Song et al. (2016, 2018) found a gap of 5–8% for Polypedilum. However, the average genetic distance for S. gibbus is up to 9.1% (ranging from 0 to 13.0%), and for S. okiabbus is 3.95% (ranging from 0 to 14.4%) clearly larger than the defined threshold. Therefore, the vouchers of the species await to be checked to resolve the problem.

Table 1.
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GenBank accession data used in the analysis; * data from this study.

Species Sample ID GenBank Accession Species Sample ID GenBank Accession
Stenochironomus annulus ZJCH220, * ON002477 Stenochironomus linanensis ZJCH251, * ON002473
Stenochironomus annulus ZJCH222, * ON002475 Stenochironomus okiabbus ZJCH219, * ON002483
Stenochironomus annulus ZJCH223, * ON002480 Stenochironomus okiabbus ZJCH244, * ON002479
Stenochironomus baishanzuensis ZJCH246, * ON002482 Stenochironomus okiabbus ZJCH245, * ON002474
Stenochironomus baishanzuensis ZJCH247, * ON002476 Stenochironomus okiabbus NC_061972 NC_061972
Stenochironomus baishanzuensis ZJCH226, * ON002484 Stenochironomus okiabbus NIESH0017 LC462301
Stenochironomus fascipennis ZMUO.025362 MZ657887 Stenochironomus okiabbus NIESH0026 LC462365
Stenochironomus fascipennis ZMUO.025363 MZ658663 Stenochironomus okiabbus NIESH0307 LC462355
Stenochironomus gibbus JN016848 JN016848 Stenochironomus okiabbus NIESH0746 LC462364
Stenochironomus gibbus NC_061971 NC_061971 Stenochironomus okiabbus OL753645 OL753645
Stenochironomus gibbus OL742440 OL742440 Stenochironomus sp. 1CZ OL753646 OL753646
Stenochironomus gibbus PY-32A KP902798 Stenochironomus sp. 2CZ OL742441 OL742441
Stenochironomus gibbus PY-33A KP902799 Stenochironomus sp. 3CZ OL753647 OL753647
Stenochironomus gibbus PY-34A KP902800 Stenochironomus sp.1BD HQ551963 HQ551963
Stenochironomus gibbus STE-GIB-IM-LIM28VII-254 MT535051 Stenochironomus sp.1BD HQ928366 HQ928366
Stenochironomus gibbus STE-HIB-IM-VI29VII-304 MT535060 Stenochironomus sp.1BD MF718872 MF718872
Stenochironomus gibbus ZMUO.024239 MZ657365 Stenochironomus sp.1BD MF721507 MF721507
Stenochironomus gibbus ZMUO.024238 MZ656608 Stenochironomus sp.1BD MF723892 MF723892
Stenochironomus hibernicus ZMUO.025366 MZ660623 Stenochironomus tobaduodecimus NC_061973 NC_061973
Stenochironomus hibernicus ZMUO.025367 MZ656796 Stenochironomus tobaduodecimus OL753648 OL753648
Stenochironomus linanensis ZJCH224, * ON002473 Stenochironomus zhengi NC_061974 NC_061974
Stenochironomus linanensis ZJCH249, * ON002478 Stenochironomus zhengi OL753649 OL753649
Table 2.
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Kimura 2-parameter pairwise genetic distances based on COI barcodes of twelve known Stenochironomus species from GenBank.

Species Distance
1 2 3 4 5 6 7 8 9 10 11
1. S. annulus
2. S. baishanzuensis 15.13
3. S. fascipennis 13.74 14.00
4. S. gibbus 11.17 15.58 15.51
5. S. hibernicus 16.50 15.36 14.39 14.61
6. S. linanensis 17.74 18.69 18.29 17.04 18.22
7. S. okiabbus 15.25 15.03 16.20 15.49 15.66 17.69
8. Stenochironomus sp.1BD 14.92 14.28 13.91 15.26 15.35 15.92 14.27
9. Stenochironomus sp.1CZ 18.58 17.11 17.16 18.03 21.01 19.58 19.08 15.80
10. Stenochironomus sp.3CZ 12.87 14.98 14.20 14.83 17.19 17.69 14.89 14.46 17.39
11. S. tobaduodecimus 18.11 17.05 18.11 18.32 19.08 19.04 16.12 20.12 17.40 18.83
12. S. zhengi 17.96 16.59 18.15 19.14 19.32 19.65 18.16 18.43 20.55 17.70 20.09
Figure 1. 

Neighbour-joining tree for twelve species of Stenochironomus based on K2P distance in DNA barcodes. Clade in yellow represents S. annulus sp. nov., red represents S. baishanzuensis sp. nov. Numbers on branches represent bootstrap support (>75%) based on 1000 replicates; scale equals K2P genetic distance.

Figure 2. 

Histogram of pairwise K2P distances of public Stenochironomus sequences, generated by web site of ABGD.

Taxonomy

Stenochironomus annulus Song & Qi, sp. nov.

http://zoobank.org/793EEC94-E1E4-45F7-906E-13154716B102
Figs 3, 4, 5

Type material

Holotype (BOLD & TZU sample ID: ZJCH220; Field ID: BSZ87) 1 male, China, Zhejiang Province, Lishui City, Qingyuan County, Baishanzu National Nature Reserve, 27.76°N, 119.31°E, 11–12. VIII. 2020, light trap, Qi X & Song C. Paratypes: 2 males, same data as for holotype.

Diagnostic characters

The adult males of S. annulus sp. nov. can be separated from known Stenochironomus species from China by the following combination of characters: spots on the membrane of wing restricted to RM and FCu areas; posterior portion of median vittae with little pale pigmentation; lateral vittae with stripe markings; postnotum with markings reaching the posterior margin; femur of mid and hind legs with an annulus medially on each; superior volsella cylindrical, with four long setae; inferior volsella extending beyond apex of anal point, with two or three bristles and one well-developed terminal spine.

Etymology

The specific name refers to the circular ring markings of the femur of mid and hind legs of the male adult.

Description

Male imago (N = 3). Total length 3.59–4.17, 3.87 mm. Wing length 1.95–2.03, 2.00 mm. Total length / wing length 1.75–2.05, 1.94. Wing length / length of pro-femur 1.58–1.93, 1.73.

Coloration (Fig. 3). Mature adult mostly brownish. Head yellow. Thorax yellowish except for the lateral vittae, postnotum with dark pigmentation and medial lateral with light pigmentation (sometimes difficult to observe). Membrane with 2 dark spots restricted to RM and FCu areas. Legs. Apical 3/5 of femur of P1 dark brown; apical and annulus of femur, and Ta 5 P2–P3 dark brown; basal 1/2 of tibia of P3 dark brown. Abdomen. Tergites V–IX brown.

Figure 3. 

Male adult (holotype, in lateral view) of Stenochironomus annulus Song & Qi sp. nov.

Head. AR 1.62–1.88 (2), ultimate flagellomere 680–770 µm long; Temporals 10–13, 12 setae including 5–8 inner, and 2–3 outer, verticals, postorbitals 1–3. Clypeus with 15–22, 19 setae. Tentorium 170–205 μm long, 45–53 μm wide at the widest part. Palp 5-segmented, lengths (in μm) of segments: 60–70, 66; 50–70, 60; 193–220, 203; 140–160, 152; 208–288, 248. Palpomere ratio (5th / 3rd) 1.09–1.31, 1.22.

Thorax. Dorsocentrals 16–17, 18; acrostichals 12–15, 14; prealars 5–6, 6; Scutellum with 11–13 setae in 2 rows.

Wing (Fig. 4A). VR 1.08–1.08, 1.06. Brachiolum with 2–3 setae. Distribution of setae on veins: R, 31–39, 34; R1, 28–40, 34; R4+5, 33–62, 46. Squama with 8–12, 10 setae. Anal lobe normally developed.

Figure 4. 

Male adult of Stenochironomus annulus Song & Qi, sp. nov. A wing B hypopygium in dorsal view C hypopygium in ventral view D legs.

Legs (Fig. 4D). Fore leg: width at apex of tibia 43–50, 46 μm, tibia with blunt scale 35–40, 38 µm long. Mid leg: width at apex of tibia 53–65, 59 μm, tibia with 2 apical spurs 35–38, 37 and 40–45, 43 µm long. Hind leg: tibia 60–73 μm width at apex; tibial spurs 40–43, 42 and 40–43, 42 µm long, slightly fused medially. Lengths (in μm) and proportions of legs in Table 3.

Table 3.
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Male adult of Stenochironomus annulus sp. nov. Length (in µm) and proportions of legs (N = 3).

P1 P2 P3
Fe 1060–1280, 1156 920–1110, 993 1120–1250, 1170
Ti 1050–1150, 1116 850–930, 893 1070–1100, 1060
Ta 1 1500–1700, 1610 540–720, 656 860–910, 890
Ta 2 750–820, 796 370–380, 373 460–500, 483
Ta 3 630–660, 647 270–280, 273 360–380, 370
Ta 4 440–570, 507 150–160, 156 220–220, 220
Ta 5 210–240, 230 75–90, 82 80–100, 90
LR 1.42–1.48, 1.44 0.64–0.80, 0.73 0.82–0.85, 0.84
BV 1.75–1.80, 1.78 2.65–3.10, 2.87 2.64–2.78, 2.68
SV 1.35–1.45, 1.41 2.52–3.33, 2.91 2.42–2.61, 2.50

Hypopygium (Figs 4B, C, 5). Anal point straight and parallel-sided in dorsal view, 103–113, 100 μm long and 30–43, 35 µm wide at base, 8–10, 9 µm wide at apex. Tergite IX with 19–22, 20 long setae medially and posterior margin of tergite IX with 6 strong setae and 5 spines. Laterosternite IX with 4–4, 4 setae. Transverse sternapodeme 43–50, 47 μm long; phallapodeme 78–88, 85 μm long. Gonocoxite 173–185, 181 μm long, gonostylus 205–270, 238 μm long. Superior volsella cylindrical, 40–45, 43 μm long, 20–20, 20 μm wide, with 4–5 long setae (Fig. 4C). Inferior volsella elongate, 203–228 μm long, extending beyond the apex of anal point, with 2–3 long bristles and 1 strong terminal spine. HR 0.64–0.90, 0.77, HV 1.46–1.75, 1.64.

Figure 5. 

Male adult (holotype) of Stenochironomus annulus Song & Qi sp. nov. A hypopygium in dorsal view B hypopygium in ventral view C superior volsella.

Immature stages and female unknown.

Remarks

Morphologically, S. annulus sp. nov. shows high similarity to Stenochironomus xianjuensis Zhang, Gu, Qi & Wang, 2016, on the basis of the following similar common characters: membrane of wing with similar spot patterns; cylindrical superior and inferior volsella. However, the new described species could be distinguished in having a straight and parallel-sided anal point and different leg pigmentation patterns. According to the molecular data, S. annulus is sister to S. gibbus (Fig. 1), but could be separated by thorax vittate and leg coloration (Table 4).

Table 4.
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Main differences between S. annulus sp. nov., S. baishanzuensis sp. nov., S. gibbus, and S. xianjuensis.

Thorax vittae Anal point Legs pattern
S. annulus Median vittae not obvious; lateral vittae with stripe pigmentation Anal point straight and parallel-sided With dark annulus on femur of P2 and P3
S. baishanzuensis Median vittae with little pigmentation; lateral vittae with stripe pigmentation Anal point straight and parallel-sided Entire femur of P2 pale; femur of P3 brown
S. gibbus Thorax without pigmentation Apex parallel-sided to slightly bulbous Nearly 1/2 to entire femur of P2; basal 0.12–0.30 femur of P3 dark brown;
S. xianjuensis Thorax without median vittae; lateral vittae with stripe pigmentation Apex of anal point swollen and rounded Apical 1/4 of P2 and P3 brown

Distribution

The species is currently known only from Zhejiang Province in Oriental China.

Stenochironomus baishanzuensis Song & Qi, sp. nov.

http://zoobank.org/16D79540-7339-434A-9662-29D1BB5F360B
Figs 6, 7, 8

Type material

Holotype (BOLD & TZU sample ID: ZJCH226; Field ID: BSZ93) 1 male, China, Zhejiang Province, Lishui City, Qingyuan County, Baishanzu National Nature Reserve, 27.76°N, 119.31°E, 11–12. VIII. 2020, Qi X. & Song C., collected by light trap. Paratypes: 2 males, same data as for holotype.

Diagnostic characters

Adult males of S. baishanzuensis sp. nov. can be distinguished from other related species by the following combination of characters: membrane of wing with large dark spots on median and apical parts; median vitta, lateral vitta, and postnotum with pigmentation; superior volsella short and broad with four setae; inferior volsella with four long bristles and one stout terminal spine, not overreaching apex of anal point.

Etymology

The specific name refers to the Baishanzu National Nature Reserve, where the holotype was collected.

Description

Male imago (N = 3). Total length 3.98–4.22, 4.07 mm. Wing length 1.90–2.13, 2.05 mm. Total length / wing length 1.87–2.22, 1.99. Wing length / length of pro-femur 1.63–1.65, 1.64.

Coloration (Fig. 6). Head. Antennal hairs dark; palpomeres dark. Thorax almost pale yellow, with posterior portion of media vitta, posterior 3/4 portion of postnotum, and almost the lateral vitta dark brown. Membrane with 2 dark spots located around RM and FCu areas (median spot is darker). Legs. P1: knee, tibia and Ta 1 dark brown, basal 3/4 of femur and Ta 2–5 pale yellowish; P2: yellowish with brownish knee; P3: yellowish with brownish knees and tibia. Abdomen almost light brown with T VI–VII dark brown.

Figure 6. 

Male adult (holotype, in dorsal view) of Stenochironomus baishanzuensis Song & Qi sp. nov. male.

Head. AR 1.93, ultimate flagellomere 810 µm long (n = 1); Temporals 12–15, 13 setae, including 5–7, 6 inner and 4–6, 5 outer verticals and 2–3, 3, postorbitals. Clypeus with 14–20, 18 setae. Tentorium 155–193, 170 μm long, 35–53, 44 μm wide. Palp 5-segmented, lengths (in μm) of segments: 42–55, 47; 43–65, 53; 200–223, 214; 130–155, 146; 232–275, 253. Palpomere ratio (5th / 3rd) 1.13–1.26.

Thorax. Dorsocentrals 15–16, 15; acrostichals 12–15, 14; prealars 6–7, 7. Scutellum with 8–9, 9 setae in 2 rows.

Wing (Fig. 7A). VR 1.05–1.06, 1.06. Brachiolum with 2 setae. Distribution of setae on veins: R, 30–32, 31; R1, 22–26, 25; R4+5, 36–42, 39. Squama with 10–11, 11 setae. Anal lobe normally developed.

Figure 7. 

Male adult (holotype) of Stenochironomus baishanzuensis Song & Qi, sp. nov. A wing B hypopygium in dorsal C hypopygium in ventral view D legs.

Legs (Fig. 7D). Fore leg: apex of tibia 55–61, 58 μm width, tibia with pointed scale 35–38 µm long. Mid leg: apex of tibia 60–68, 65 μm width; tibial spurs 48–55, 51 and 45–55, 49 µm long, completely fused at midline part. Hind leg: apex of tibia 60–68, 64 μm width, tibia with 2 apical spurs 37–50, 47 and 35–47, 41 µm long. Lengths (in μm) and proportions of legs in Table 5.

Table 5.
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Male adult of Stenochironomus baishanzuensis sp. nov. Lengths (in µm) and proportions of legs (N = 3, except where otherwise stated).

P1 P2 P3
Fe 1150–1300, 1250 970–1110, 1053 1140–1310, 1243
Ti 1130–1280, 1230 870–930, 907 1050–1250, 1160
Ta 1 1250 (N = 1) 480–700, 606 820–950, 900
Ta 2 800 (N = 1) 370–400, 387 450–520, 477
Ta 3 680 (N = 1) 300–340, 317 380–410, 397
Ta 4 560 (N = 1) 180–210, 200 230–260, 240
Ta 5 270 (N = 1) 90–100, 95 90–110, 100
LR 0.98 (N = 1) 0.52–0.75, 0.67 0.76–0.78, 0.77
BV 2.35 (N = 1) 2.46–2.64, 2.57 2.59–2.94, 2.72
SV 2.06 (N = 1) 2.91–4.17, 3.31 2.66–2.67, 2.67

Hypopygium (Figs 7B, C, 8). Anal point 110–125, 120 μm long, 30–45, 35 µm wide at base, 10–13, 12 µm wide at apex. Tergite IX with 18–23, 20 long setae medially, and 3–4, 4 setae laterally. Posterior margin of tergite IX with 3–4, 4 spines and 5–7 long setae each side. Transverse sternapodeme 38–53, 44 μm long; phallapodeme 95–113, 105 μm long. Gonocoxite 183–188, 185 μm long. Gonostylus 218–25, 221 μm long. Superior volsella short and broad, 13–15, 14 μm long, 18–25, 21 μm wide, with 4 long setae (Fig. 7C). Inferior volsella elongate, 183–192, 187 μm long, extending at most, to apex of anal point, with 4 setae and 1 strong terminal spine. HR 0.83–0.84, .084, HV 1.77–1.93.

Figure 8. 

Male adult (holotype) of Stenochironomus baishanzuensis Song & Qi, sp. nov. A hypopygium in dorsal view B hypopygium in ventral view C superior volsella.

Immature stages and female unknown.

Remarks

The male adult of S. baishanzuensis sp. nov. resembles that of S. gibbus (Fabricius, 1794) in the structure of the hypopygium and the wing patterns, but can be separated by the following characters: straight and parallel-sided anal point, and legs bearing different patterns (Table 4).

Distribution

The species is currently known only from Zhejiang Province, Oriental China.

Stenochironomus okialbus Sasa, 1990

Figs 9, 10

Stenochironomus okialbus Sasa, 1990: 122, fig. 10.

Material examined

3 male adults, collected by light trap in Zhejiang Province, Lishui City, Qingyuan County, Baishanzu National Nature Reserve, 27.76°N, 119.31°E, 11–12.VIII.2020, leg. Song C.

Figure 9. 

Male adult of Stenochironomus okialbus (in lateral view): new record to China

Diagnostic characters

Stenochironomus okialbus differs from other related species by a combination of characters: wing with dark markings in the middle and apex; superior volsella short and small, spatulate, with four or five long setae; inferior volsella elongate, with 2–4 long setae and a slender terminal spine; posterior margin of tergite IX with 8–10 setae and eight spines.

Description

Male imago (N = 3). Total length 2.94–3.98, 3.62 mm. Wing length 1.80–1.85 mm. Total length / wing length 1.85–2.20, Wing length / length of pro-femur 178–1.88.

Coloration (Fig. 8). Body almost pale yellowish or white, except postnotum with spot area and tergite IV–VII brown; wing with dark pigmentation on median and apical parts; all legs pale yellow with dark knees and apex of tibia.

Head. AR 1.10–1.25, 1.12, ultimate flagellomere 430–660, 580 µm long. Temporal with 12–16, 14 setae, including 7–8, 7 inner verticals, 4–7, 6 outer verticals and 1–2, 2 postorbitals. Clypeus with 12–20, 17 setae. Tentorium 155–220, 190 μm long, 30–53, 44 μm wide. Palpomere lengths (μm): 33–48, 37; 40–65, 55; 123–195, 170; 85–125, 116; 130–218, 194. Palpomere ratio (5th /3rd) 1.05–1.21, 1.13.

Thorax. Dorsocentrals 14–21, 18; acrostichals 9–12, 11; prealars 5–6, 6; Scutellum with 7–12 setae in two rows.

Wings. VR 1.06–1.10, 1.08. Brachiolum with 1–2, 2 setae. Distribution of setae on veins: R, 20–29, 25; R1, 21–39, 31; R4+5, 49–53, 51. Squama with 10–18, 14 setae. Anal lobe normally developed.

Legs. Fore leg: width at apex of tibia 53–63, 58 μm, tibia with blunt scale 35–50, 44 µm long. Mid leg: width at apex of tibia 53–70, 61 μm, tibia with two apical spurs 43–53, 48 and 45–58, 52 µm long. Hind leg: width at apex of tibia 58–73, 64 μm, tibia with two apical spurs 45–55, 51 and 45–56, 52 µm long. Lengths (in μm) and proportions of legs as in Table 6.

Table 6.
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Male adult of Stenochironomus okialbus. Lengths (in µm) and proportions of legs (N = 3, except where otherwise stated).

P1 P2 P3
Fe 920–1310, 1150 790–1220, 1053 930–1350, 1183
Ti 930–1210, 1050 730–1030, 913 870–1230, 1083
Ta 1 1200–1640 (N = 2) 530–730, 653 710–990, 880
Ta 2 590–810 (N = 2) 290–410, 360 380–520, 470
Ta 3 500–680 (N = 2) 230–310, 277 290–410, 363
Ta 4 450–650 (N = 2) 140–210, 180 180–250, 230
Ta 5 210–300 (N = 2) 60–100, 87 80–110, 97
LR 1.45–1.48 (N = 2) 0.70–0.73, 0.72 0.80–0.82, 0.81
BV 1.63–1.69 (N = 2) 2.84–2.94, 2.90 2.69–2.75, 2.71
SV 1.42–1.46 (N = 2) 2.88–3.08, 3.00 2.53–2.61, 2.57

Hypopygium (Fig. 10). Anal point 110–125, 118 μm long, 43–60; wide, 52 µm width at base, 18–20, 18 µm at apex; slightly swollen and rounded apically. Tergite IX with 19–25, 22 long setae on median part; posterior margin of tergite IX with 6 strong setae and 3 spines. Laterosternite IX with 3–4, 4 setae. Transverse sternapodeme 35–48, 41 μm long; phallapodeme 85–95, 89 μm long. Gonocoxite 138–175, 159 μm long. Gonostylus 185–200, 196 μm long. Superior volsella short, 25–30, 28 μm long, 23–25, 24 μm wide, with 4–5 long setae. Inferior volsella linearly elongate, 183–220, 208 μm long, with 2–3 long setae and 1 stout terminal spine. HR 0.74–0.86, 0.81; HV 1.58–1.97, 1.84.

Figure 10. 

Male adult of Stenochironomus okialbus. A hypopygium in dorsal view B hypopygium in ventral view C superior volsella.

Remarks

The morphological characters of the Chinese specimens fit well with the original description and illustrations provided by Sasa (1990): wing with two spotted areas; narrow dark rings on knee points; anal point slightly swollen and rounded. However, some relevant differentiating characters were observed within the examined specimens: the inferior volsella have only two or three long setae, while it bears four in the Japanese specimens; average values of the AR 1.10–1.25 are lower than 1.37–1.41 in the Japanese species.

According to the molecular data, specimen (LC462365) of Stenochironomus okialbus, shows a large genetic distance to other specimens (up to 14%); as the specimen is not accessible it should be rechecked. The K2P distance between Japanese and Chinese specimens is 1.7%, which well supports them as the same species.

Distribution

Oriental China (Zhejiang) and Japan.

Stenochironomus linanensis Qi, Lin, Liu & Wang

Stenochironomus linanensis Qi et al. (2015): 114.

Material examined

3 male adults collected by light trap, leg. Qi X.; Zhejiang Province, Lishui City, Qingyuan County, Baishanzu National Nature Reserve, 27.76°N, 119.31°E, 11–12.VIII.2020.

Diagnostic characters

Stenochironomus linanensis differs from other related species in having: wing transparent; body yellow; superior volsella finger-like with nine long setae; inferior volsella elongate, with four long setae and one strong terminal spine; tergite IX with 10–15 long setae located medially.

Distribution

Oriental China (Zhejiang).

Stenochironomus satorui (Tokunaga & Kuroda, 1936)

Chironomus (Stenochironomus) satorui Tokunaga & Kuroda (1936): 2.

Stenochironomus satorui Qi et al. (2011): 226.

Material examined

2 male adults collected by light trap, leg. Song C., Zhejiang Province, Lishui City, Qingyuan County, Baishanzu National Nature Reserve, 27.76°N, 119.31°E, 11–12.VIII.2020.

Diagnostic characters

Wing with median band; posterior edge of tergite IX with 14–15 long setae; anal point slender parallel-sided, with pointed apex; superior volsella short and finger-like, with four or five setae; inferior volsella with one median seta and three apical setae.

Distribution

China (Zhejiang, Hainan, Guizhou, Xizang); Japan.

Updated key to known adult males of Stenochironomus from China

The following key updates Lin et al. (2021) and Qi et al. (2015)

1 Inferior volsella with a well-developed terminal spine 2
– Inferior volsella without a well-developed terminal spine 12
2 Wing membranes with dark pigmentation 3
– Wing membranes without any pigmentation 8
3 Legs almost entire brown; wing with dark pigment restricted to a part area 4
– Legs yellow; entire wing smoky gray S. maculatus Borkent, 1984
4 Wing with two dark spots restricted to RM and FCu areas 5
– Wing with dark median band 6
5 Anal point straight and parallel-sided S. annulus Song & Qi, sp. nov.
– Apex of anal point swollen and rounded S. xianjuensis Zhang et al., 2016
6 Anal point bullous, knees of fore femur dark brown 7
– Anal point almost parallel-sided, fore femur dark brown S. baishanzuensis Song & Qi, sp. nov.
7 Mid and hind legs without pigmentation except knees S. okialbus Sasa, 1990
– Apical 0.23 to entire hind-femur with dark pigmentation S. gibbus (Fabricius, 1805)
8 Apex of anal point swollen and rounded 9
– Apex of anal point not swollen and rounded 11
9 Superior volsella with 9–12 setae; posterior margin of tergite IX with 10–14 setae and 4–8 spines 10
– Superior volsella with four setae; posterior margin of tergite IX with 14–16 setae S. koreanus Borkent, 1984
10 Superior volsella much beyond posterior margin of tergite IX; anal lobe reduced S. zhengi Lin & Liu, 2021
– Superior volsella small, finger-like; anal lobe developed S. linanensis Qi, Lin, Liu & Wang, 2015
11 Posterior edge of tergite IX with eight long setae and six spines; anal point parallel-sided S. macateei (Malloch, 1915)
– Posterior edge of tergite IX with 14 long setae, without any spine; anal point roughly triangular, apically pointed S. mucronatus Qi, Shi & Wang, 2008
12 Wing membranes with dark pigmentation 13
– Wings without any pigmentation or with narrow pigment areas around RM and along veins M3+4 and Cu1 12 15
13 Abdominal tergites I–IV light yellow, tergites V–VIII light brown, hypopygium dark brown 14
– Abdomen and hypopygium light yellow S. inalemeus Sasa, 2001
14 Preepisternum with brown spots; anal point apically rounded S. nubilipennis Yamamoto, 1981
– Preepisternum without any pigmentation; anal point apically pointed S. satorui (Tokunaga & Kuroda, 1936)
15 Posterior margin of tergite IX without spines 16
– Posterior margin of tergite IX with spines S. brevissimus Qi, Lin, Liu & Wang, 2015
16 Entire body yellow, without dark pigmentation; inferior volsella with three long setae S. hainanus Qi, Shi & Wang, 2008
– Body yellow, with brown spots on thorax, abdomen, hypopygium and legs; inferior volsella with six long setae S. totifuscus Sublette, 1960

Acknowledgements

The authors are grateful to financial support from the National Natural Science Foundation of China (NSFC, Grant No. 32070481, 32100353), the Zhejiang Provincial Natural Science Foundation of China (Grant No. LY22C040003), the Science & Technology Project of Taizhou (Grant No. 21hb04, 21nya17, 1902gy23), and the Project of Biodiversity Survey in Lishui Municipality, Zhejiang Province of China.

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