Northern Chironomus: C. islandicus

Species 5s. C. islandicus (Kieffer, 1913)

In Bold Bin: BOLD:AAI4308
Some specimens identified as C. islandicus from Iceland and also from North America. This is the first indication that this species may occur in the Nearctic, but unfortunately no morphological data are given.
The nearest neighbor is C. sp. h in BOLD Bin: BOLD:AAP3010

Adult similar to C. hyperboreus. The species was redescribed by Pedersen (1978) along with the cytology. Wülker and Butler (1983) also described the polytene chromosome sequences and some larval characters and Stur and Ekrem (2020) gave further information on the adults and some photographs of some larval characters.

Male:
Wing length 4.9 (3.7-5.5) mm. AR 5.0 (4.5-5.5); LR1 1.12 (1.06-1.17); LR2 0.58 (0.53-0.60); LR3 0.67 (0.62-0.72). BR 5.7 (5.1-6.3).
Head black. Thorax with black ground color, with pruinose areas on antero-lateral and posterior-median parts of scutum and some pruiescense on the pleural sclerites.
Scutellum and postnotum black, halteres dirty white.
Thoracic setae: acrostichal 21 (13-34), dorsolaterals 58 (34-84), prelars 12 (8-16).
Legs black-brown with tarsal segments a little paler.

Male hypopygium of C. islandicus (BOLD Fi36+1346868292)

Abdomen black, posterior margins of segments paler. TIX with about 9 setae in individual pale spots.
Anal point relatively broad; Superior volsella long E(i) type of Strenzke (1950); Inferior volsella long, beyond the end of the anal point and about to midpoint of gonostylus, slightly turned out at tip; gonostylus relatively narrow and narrowing markedly over terminal quarter to fifth.

Female: Not described.

Pupa: (From Langton & Visser 2003): Exuvial length 9.0-12.0 mm.
Exuviae golden brown to dark brown, without marked contrast in color between thorax and abdomen; outer margin of the anallobes colored except at base.
Cephalic tubercles conical, 80x105-160x120 µm; frontal setae 45-72 µm long. Basal ring of thoracic horn 145x80-175-90 µm, HR 1.81-1.94. Thorax less distinctly granulate, anteriorl granules small and distinct, medially most are somewhat flattened, producing an irregular reticulate pattern, or evanescant.
Hook row of segment II entire, 0.47-0.57 times the tergite width, with 97-137 hooks.
Armament of tergites II-VI not so strongly waisted and with the posterior transverse band not successively increasing in extent to tergite VI; usually reduced on VI. Shagreen of sternite II continuous from postero-lateral corner to seta V5, the region between containing points of similar size to those on each side. Both sternites III and IV with lateral longitudinal bands of shagreen. Sternite IV postero-laterally bare, without a patch of enlarged points. Pleura of segment IV spinulate.Caudolateral spur of segment VIII with 2-7 stout teeth. Fringe of anal lobe with 102-137 taeniae.

Fourth instar larva: (From Wülker & Butler 1983) a salinarius-type, although small humps may be present at rear of segment XI.
Posterior of gula darkened, a small dark stripe at rear of frontoclypeus and lobed dark spot near front, but high individual variability.
Antenna - A1 201; A2 30; A1 about 4.2 times longer than wide.
In Svalbard specimens the proportions are about 78 : 27 : 7.5 : 14 : 6; AR abt 1.6. RO about a third up from base of segment; A1 about 3 times longer than wide.

BOLDBJ149-556
Mentum width about 140 µm, with central tooth type IIA; 4th lateral not reduced (type I). Pecten epipharyngis with about 8 teeth; mandible with third inner tooth separated and partly colored (type IIIB); MTR about 0.27

Cytology: Four polytene chromosomes with the thummi arm combination AB, CD, EF, G.
Centromeres relatively heterochromatic. Arm G small, with a virtuallly terminal nucleolus but it is not the major nucleolus and is not always developed; with at least three other BRs - the major one proximal in arm B and two other minor ones in arm E, at least one of which may not always be developed. Arm G is usually unpaired and sometimes attached to the centromere of chromosome CD.

isl A1: 1a - 2c, 10a - 12c, 3i - 2d, 9e - 4a, 13a - 19f i.e. as holomelas, cucini, magnus, etc.
isl B1: Nucleolus proximal in arm B, banding unclear.
isl C1: 1 - 6b, 15c-e, 8 - 11c, 15b - 11d, 6gh, 17a - 16, 7d-a, 6f-c, 17b - 22 i.e. as cucini, sp. 3b.
isl D1: distal bands identical to those of tardus, cucini, cucini, mangnus, but unspecified changes nearer the centromere.
isl E1: possibly 1 - 3e, 5 - 10b, 4 - 3f, 10c - 13 but difficult to be certain due to the 2 nucleoli i.e. possibly as aberratus, tardus, cucini, hyperboreus, sp. h, etc.
isl F1: possibly 1-10, 17-11, 18-23 i.e. as cucini, tenuistylus, tardus, etc.

Found: Nunavut - Kitikmeot (69.2187°N, 104.926°W) (BOLD)
Iceland (Type locality); Stoedurvatned, Kvisker (68.9838°N, -16.4371°W) (BOLD); Thingvallavatn; Myvaten (Wülker
& Butler 1983).
Norway - Svalbard, Bear Island (74.4814°N, 19.0048°E); Jan Mayen Island (abt. 72°N; -7.5°W) (Stur & Ekrem 2020); Lebesby, Finnmark (70.441°N, 26.805°E); Melhus, Sor-Trondelag
(63.2171°N, 10.3076°E), (all BOLD)

The cytology indicates that this species is clearly closely related to a group of northern species, such as C. hyperboreus, C. cucini, C. magnus (Wülker & Butler 1983) and C. species h, as all have heterochromatic centromeres and a small arm G and most with multiple nucleoli in the long chromosomes, some of which appear to correspond. As well, the males of both species have a similar Superior volsella. The adult is very similar in coloration to C. hyperboreus, but can be differentiated by the lower LR.
Langton & Visser (2003) distinguish the pupa by the lack of setae on postero-lateral of sternite IV (the couplet seems to imply that this means there is no pedes spurii A).