Holarctic Chironomus: C. riparius

Chironomus riparius Meigen, 1804

Possible synonym: Chironomus ginzanbeceus & Chironomus ginzanbeus Sasa & Suzuki 2001 (Yamamoto & Yamamoto 2018))
Incorrect synonym - Chironomus lugubris Tokunaga 1938 (Sasa & Yamamoto 1977)

In BOLD Bin: BOLD:AAA7263.

C. riparius is a member of a species group and currently can only be accurately identified from the BOLD barcode sequence or the larval polytene chromosome banding patterns.

Adult (based on U.S. material):

Male:

Wing length about 3.7-4.3 mm., width abt. 1.05 mm. AR 3.2-3.6. LR about 1.6-2.95.
Ground color pale to dark brown, thoracic markings red-brown to blackish brown; legs pale green to light brown towards their bases, tarsal segments darker; abdomen brown to blackish, apical 0.25 of each tergite pruinose and pale.
Specimens from colder habitats are darker.
Head: Frontal tubercles small 10-30 x 15 µm (l/w 1.5-2), clypeus rather small (0.66-0.72 of diameter of antennal pedicel) with 34-39 setae. Palpal proportions (micron): 69 : 69 : 129 : 130 : 191 (P5/P4 - 1.47; P5/P3 - 1.48).
Some thoracic setae: Dorsocentral - 27-33; Prealar - 6-7; Supraalar - 1-2; Scutellar - about 24 setae; 9 in 2 rough anterior rows and 15 larger setae in posterior row. Leg lengths (micron) and proportions (1 specimen):

Male	Fe	Ti	Ta1	Ta2	Ta3	Ta4	Ta5	LR	F/T	BR
PI	1530	1465	2005	1745	825	760	345	2.95	1.04	2.23
PII	1595	1595	925	530	385	260	185	0.58	1.0
PIII	1870	1975	1330	810	610	365	220	0.67	0.95

BR 2.05-2.95 (i.e. no beard); M.Sens.chaetae 13-14.

Terminalia of adult male

About 3-10 setae in individual pale spots (which may be closely packed) on tergite IX.
The Superior Volsella is Strenzke's S(b) type; Inferior volsella long, reaching to about middle of gonostyle, with simple setae. Gonostyle only moderately swollen and narrows gently from about midpoint or more rapidly over posterior 2/3. Anal point narrow at base and widening at distal end.

Female: According to Townes (1945), similar to male except for usual sexual differences. About 13 setae on the crescent shaped segment X, which is about 3.3 times longer than the greatest width. Morisch & Wülker (1987) Fig. 1 shows the cercus to have a relatively pointed posterior end, with a significant ventral bulge.

From Morisch & Wülker 1987

Fourth instar larva (from Chavan et al. 2013): A thummi-type larva, length up to 5.4 mm. Most of description just generic for Chironomus. Frontoclypeus and gula darkened, gula over posterior half and widest at posterior margin. Ventromentum about same width as the mentum, VMR about 0.25. Central tooth of mentum type 1B. Premandible of type B2. PE with 13 teeth.

C. riparius (N.A.) mouthparts

Found: INDIA - unconfirmed record from Kasar Lake, Dharur (18.92°N, 76.20°E), Bindusara River, Beed (18.90°N, 75.73°E),
both Maharashtra (Chavan et al. 2013).
JAPAN - Ginzan, Yoichi, Kamikawa (Sasa & Suzuki (2001); Lake Akan, Kushiro, Akan National Park, Shizunai River,
Hidaka Gun, Tokachi, Obihiro; all Hokkaido.
RUSSIA - Novosibirsk Province and other localities in Eastern Russia (Kiknadze et al. 2016).

Many of these records are unconfirmed and may actually refer to related species. As well, the cytology and COI sequence has not been reported to help confirm identity. Only the Kiknadze et al. 2016 identification can be considered reliable. If it does occur, it seems to be relatively rare.

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