Endochironomus pekanus ( Kieffer, 1916 )

Li, Zixuan & Tang, Hongqu, 2024, Description of immature stages of Endochironomus pekanus (Kieffer) (Diptera, Chironomidae), Zootaxa 5446 (4), pp. 581-587 : 581-585

Endochironomus pekanus ( Kieffer, 1916)

( Figs 1–3 )

Tendipes pekanus Kieffer, 1916: 105 .

Endochironomus pekanus ( Kieffer, 1916) : Ree & Kim 1981: 146, Sasa & Kawai 1987: 21, Chaudhuri & Chattopadhyay 1990: 158.

Endochironomus tendens [nec Fabricius, 1775: 752]: Qi et al. 2011: 220, partim.

Endotribelos redimiculum Qi, Shi, Lin & Wang, 2013: 286 . Syn. n.

Material examined. 15 males and 1 pharate male with retained pupal exuviae, CHINA: Hubei Province, Huanggang City, Baitan Lake , 21.x.2023, ZX Li, YR He & X Dong; 1 pupate larva, 1 pupal exuviae , 6 males, Jiangxi Province, Nanchang City, Lake Poyang , 18.vii.2014, HQ Tang ; 1 male, 1 pupal exuviae, Jiangxi Province, Jiujiang City, Zhushi Lake , 06.xi.2023, ZY Ni ; 1 male, Heilongjiang Province, Mudanjiang City, Jingpo Geopark , 14.viii.2014, HQ Tang ; 2 males, Liaoning Province, Benxi City, Xinbin County, Liaohe catchment, north branch of Taizi River , site T70 , 15.viii.2009, CB Duan ; 2 males, Shandong Province, Jijing City, Grand Canal , 15.x.2018, HQ Tang ; 1 male, Jiangsu Province, Nanjing City, Lake Pipa , 07.ix.2019, HQ Tang .

Other examined material. 2 males ( NK), labelled, “ Endochironomus tendens ”, CHINA: Guizhou Province, Lipo County, 3.viii.1995, W. Bu; 1 male ( NK), labelled, “ Endochironomus tendens ”, Inner Mongolia Autonomous Region, Bayanzhaer City, Lake Wuliangsu , 3.viii.1988, X. Wang; 2 larvae ( JNU), 2 pupal exuviae ( JNU), SOUTH KOREA: Sangju City, Nakdong River , 15.ix.2017, HQ Tang. Holotype of Endotribelos redimiculum : male ( NK), CHINA: Zhejiang Province, Sanmen County , 28.vii.2010, XL Lin.

Description. Adult male. Abdominal tergites I–VII ( Figs 1A, B ) each with dark stripes medially and laterally. Foreleg with one triangular tibial scale; mid and hind legs each with two narrowly separated tibial combs, occupying about half of tibial circumference; each comb ( Figs 1C–E ) with a short spur. Hypopygium as Fig. 1F .

Pupa (n = 6). Total length 6.0–8.5, 7.8 mm.

Coloration. Exuviae generally gray-brown. Apophyses and anterior and posterior spine patches on abdominal tergites dark brown to black. Apical brush of anal lobe dark.

Cephalothorax. Frontal apotome rugulose, with low mounds; frontal setae 50–70, 66 µm long, shorter than distance between these setae. Anterior 2 dorsocentrals and posterior 2 separately grouped; Dc 1 and Dc 4 40–50, 48 µm long, Dc 2 and Dc 3 70–80, 74 µm long. Basal ring oval, 100–125, 118 µm long, and 40–55, 48 µm wide. Row of small tubercles arranged along median suture of scutum.

Abdomen ( Fig. 2A ). T I without any spinulation. T II–VIII with more or less extensive spinulation; spinulation weak on T VII–VIII. T IX with anterior spinulation. T II–VI with anterior and posterior transverse spine bands; posterior bands medially interrupted narrowly; spines of anterior bands stronger than those of posterior bands. T II with row of 35–45, 39 posterior hooks, occupying 0.46–0.50, 0.48 width of segment. All conjunctives bare and pedes spurii A absent. Pedes spurii B present only on segment II, well developed. Anal comb ( Fig. 2B ) with 3–7, 5 teeth; usually one dominant tooth 48–50, 49 µm long, flanked by 2–3 small side teeth. Spinulation on S I–VIII weak; spinules sporadic, faint. S II ( Fig. 2C ) posteromedially with a brown marking. Segment I with 1 L-seta; II–VI each with 3 L-setae; VII with 4 taeniate setae, occasionally L 1 and L 2 weak; VIII with 4–5, 5 taeniate setae, 3 posterior setae grouped. Anal lobe 520–600, 558 µm long, 1.54–1.7, 1.64 times as long as broad, with more than 150 lateral setae of equal length, arranged in bi- or triserial rows; one dorsal seta present. Male genital sac nearly as long as anal lobe.

Larva (n = 3). Total length 8.0–10.5, 8.9 mm. Postmentum 345–352, 350 µm long.

Coloration. Head capsule generally yellow, with dark brown mental teeth and mandible teeth. Ventral occipital margin dark brown.

Head (n = 2). Length 700–850 μm, cephalic index 0.65–0.72. Lengths of antennal segments (µm): 105–110, 35–37, 20–23, 15–17, 5–7. AR 1.2–1.3. Basal segment 4.2–4.4 times as long as width, with ring organ located 1/5 from base; blade 60–70 μm long, reaching apex of 4th segment. Second segment with style, somewhat shorter than its segment. Premandible 142–150 μm long, with 2 apical and one inner teeth. Pecten epipharyngis consisting of 3 plates, each stacked with 10–12 small round teeth on surface. Mandible 240–265 µm long, with one short apical tooth and 3 inner teeth; inner margin with one spine; seta subdentalis 147–150 µm long, reaching apex of most proximal inner tooth. Mentum ( Fig. 3A ) 175–180 μm wide, with 3 median and 6 pairs of lateral teeth, 1st and 4th lateral teeth distinctly shorter than neighboring teeth. Ventromental plate 170–175 µm wide, 2.18–2.30 times as long as height; inter-plate distance 90–100 µm. Maxilla ( Fig. 3B ) with 6–8 teeth on anterior margin of cardo. Distance between setae submenti 190–200 µm long.

Body ( Fig. 3C ). Procercus with 8 anal setae, 850–900, 880 µm long. Supraanal setae 460–550, 500 µm long. Anal tubules 250–300, 280 µm long, distinctly shorter than posterior parapods.

Ecology and distribution. Endochironomus pekanus is a rare species that is difficult to obtain abundantly by routine sweeping during summer seasons in North China. However, the second author observed a slight emergence peak in the middle of autumn when the temperature dropped. Since the larvae are usually found in ponds or lakes with water thymes ( Hydrilla spp. ), they are likely closely associated with this submersed perennial macrophyte. Currently, Endochironomus pekanus has been recorded in nine provinces in China, including Heilongjiang, Liaoning, Shandong, Jiangsu, Hubei, Jiangxi, Taiwan and Guizhou ( Qi et al. 2011, 2013).

Figures

FIGURE 1. Endochironomus pekanus (Kieffer), male.A–B) Habitus; C–E) tibial apices of foreleg (C), middle leg (D) and hind leg (E); F) hypopygium.

FIGURE 2. Endochironomus pekanus (Kieffer), pupa. A) Abdomen, dorsal view; B) lateral taeniate setae and anal comb on segment VIII; C) sternites II–III, red arrow indicating posterior dark marking.

FIGURE 3. Endochironomus pekanus (Kieffer), larva.A–B) Mentum, ventromental plates and maxillae; C) anal segments with developing pupal anal comb, red arrow indicating emergent anal comb.