Species 5i Chironomus laetus Belyanina & Filinkova 1996.
(This is technically a junior homonym of laetus Meigen 1818 which is now in Polypedilum)

Adult:

Male: Color dark blackish-brown, halteres pale; abdomen with a thin pale stripe at the posterior margin of segments II-VII (not recorded in type material); legs apparently paler, knees slightly darkened.
Body length 8.5-9.5 mm; wing length 4-5.5 mm; width about 1.1 mm, VR about 1.0; 2-4 SCf on brachiolum; anterior veins slightly darkened.

Adult male of C. laetus from Greenland (BOLD Database as 8TE)

AR 4.2-5.4.  Palps pale, segment lengths (micron) 71 : 80 : 307 : 288 : 371; P5/P4 1.29, P5/P3 1.21.  Frontal tubercles 49 (43.8-52.5) µm long, 12.5 µm wide (4.1 times longer than wide).
Thoracic setae: 6-12 acrostichal; 36-64 dorsocentral; 6-14 prealar; 2 supra-alar; 44-50 scutellar.
Legs with a weak beard, BR 1-1.5; LR1.3-1.4.  Approximate proportions (micron):

	Fe	Ti	Ta1	Ta2	Ta3	Ta4	Ta5	LR	F/T	BR
PI	1665	1765	2600	1170	750	645	265	1.48	1.07	low
PII	1715	1590	950	570	540	490	280	0.65-0.70	1.05
PIII	2140	2460	1715	945	600	490	245	0.65-0.70	abt 0.8

Setae of TIX not specified but shown as in a small patch.  Superior volsella of c-type of Strenzke (1959); Inferior volsella slightly longer than anal point, to about a third of gonostylus, which is relatively narrow and narrows evenly along its length.  Anal point short and broad (about twice as long as wide, narrowing slightly along its length.

Male (left) and female (right) hypopygia

Female: Coloration as in male but both scutellum and postnotum brown; sternite VIII the same color as sternite VII.
Body length 7-10 mm; wing length 5.5-6.0 mm; FT 27.1 (18.8-31.3) long and 12.5 µm wide.  LR 1.45; BR 0.85-1.
Wing length 5.5-6 mm; 2-4 SCf on brachiolum.
Thoracic setae: 8-14 acrostichal; 55-61 dorsocentral (incl. humeral); 7-12 prealar; 2 supra-alar; 63-76 scutellar.
GcIX with 6-10 setae; TX with dark anterior margin and 12-14 setae, about 3 times longer than greatest width.  Cerci described as lobe-like (as in ear?) with a large swelling at base of ventral margin.

Pupa: Exuvia with grey pattern.  Cephalothorax, lateral margins of tergites V-VIII, scala pattern on tergites I-VII, and anal lobe brown.  Tergites, except first one, covered with small spinelets to varied extent.  Spur of segment VIII broad with about 8 open spines.

Pupa (left) and larval head (right)

Fourth instar larva:  The larva is a thummi-type larva, with LP noted as longer or equal to length of posterior parapods.  Length 15-18 mm.  Head capsule width 754.2 µm; with very dark posterior 2/3 gula, wider than the mentum, which is 216.3 (212.5-225) µm wide.  Mentum of type I and central tooth possibly type IIA.  Ventromentum with smooth anterior margin, about 225.5 µm wide; about 1-1.06 times the mentum width; with 44-56 striae.  Pecten epipharyngis with 13-15 teeth.  Premandible with usual two teeth, but no other details.
Antenna with basal segment 37.5-43.6 µm wide at base, RO about a third up from base, AR 1.7-1.8.

Larva of C. laetus from Manitoba, Canada (BOLD database)

Anal tubules appear to be relatively long and possibly with a constriction in the middle.

Cytology: (based on Russian, i.e. type, material) 4 polytene chromosomes.  The original photograph of the polytene chromosomes in Belyanina and Filinkova (1996) was not clear (see below) and the arm combination was misidentified as pseudothummi-complex.  Subsequent analysis by Bolshakov et al. (2022) clarified the new laetus arm combination AE, BC, DF, G.  This combination is derived from the pseudothummi-complex by translocation CD, BF to BC, DF probably from a member of the C. riihimakiensis-related species.  This is indicated by the banding sequences and by the 'amphora-shaped' arm G typical of that group.
laeA1  1a - 2c, 10a - 12c, 3i - 2d, 9e - 4a, 13a - 19f                                                                                                                as spAl1; spLe1A1
laeB1  1a - 2d, 22d - 21a, 7a-8a, 3c - 2e, 20g - 18a, 6f-a, 4a - 5e, 13g - 8a, 17d - 14a, 23 - 28a                                              as spAl1B2
laeC1  1a - 6b, 11c - 8a, 15e - 11d, 6gh, 17a - 16a, 7d-a6f-c, 17b - 22g                                                                           as spAl1C1, sorC2, abeC1
laeD1  1a - 3g, 11a - 18f, 7g - 4a, 10e - 8e, 18g - 24g                                                                                                              as spLe1D1
laeE1  1a - 3e, 5a - 10b, 4h - 3f, 10c - 13g                                                                                                                       as spLe1D1, plumosus, etc.
laeF1  1a -8c, 12a - 17d, 10d - 8d, 11i-a, 18a - 23f                                                                                                                   as spLe1F1
laeG1  subterminal nucleolus, narrow neck, then broadens with a BR, narrowing again before broadening with another BR - giving the typical 'amphora' appearance of the C. riihimakiensis-gp.

Polytene chromosomes of C. laetus, modified to show the correct arm combination

Molecular sequence:
mtCOI:  There is sequence in GenBank (e.g. MN676646) and in the BOLD Database as either sp. 8TE or C. laetus.

Found: Manitoba - nr. Churchill (58.738°N, -93.819°W) (BOLD).
            Nunavut - Kitikmeot, Cambridge Bay (69.2194°N, -104.92°W); Greiner Lake, Victoria Island (69.19°N, -104.93°W)(GenBank).
            Yukon Territory - (BOLD).
            Greenland - Lake Tasersuaq, Kitaa, Kujalleq (60.2643°N 44.5389°W); Narsarsuaq, Kujalleq (61.1556°N, -45.3785°W) (both BOLD).
            Russia - 38 Km. nw. Labytnangii(abt 69.41°N, 66.23°E), Polar Urals (Type locality); Yamal Peninsular (Bolshakov et al. 2022).