Procladius frigidus ( Holmgren, 1869 )

Procladius frigidus ( Holmgren, 1869) View in CoL

Tanypus frigidus Holmgren, 1869 View in CoL — Holmgren (1869), Norway, adult male, adult female, description.

Procladius crassinervis ( Zetterstedt, 1838) View in CoL — Goetghebuer & Lenz (1936a), Goetghebuer & Lenz (1936b), Norway, adult male in part, key, description.

Procladius crassinervis ( Zetterstedt, 1838) View in CoL — Roback (1966b), Greenland, adult male, description, illustrations.

Procladius gretis Roback, 1971 View in CoL — Roback (1971), Canada, adult male, key, description, illustrations.

Procladius sp. A — Roback (1971), Canada, adult male, key, description, illustrations.

Procladius frigidus ( Holmgren, 1869) View in CoL — Stur & Ekrem (2020), Norway, adult males, adult females, larva, descriptions, illustrations.

Procladius crassinervis ( Zetterstedt, 1838) View in CoL — Ratnasingham et al. (2024), Canada and Greenland, adult males, adult females, photos.

Procladius frigidus ( Holmgren, 1869) View in CoL — Ratnasingham et al. (2024), Norway, adult males, adult females, pupa, larvae, photos.

Procladius pectinatus ( Kieffer, 1909) View in CoL — Ratnasingham et al. (2024), Finland, adult males, adult females, photos.

Procladius sp. — Ratnasingham et al. (2024), Finland and Canada, adult males, adult females, larvae, photos.

Material examined (n = 17). CANADA, 1 adult male (Holotype of P. gretis, CNCC ), Baffin Island , Lake Nettilling, 66.25°N 70.05°W, 30 m a.s.l., ‒9 °C m.a.t., 8.viii.1956, leg. J.G. Chillcott GoogleMaps ; 1 adult male (as Procladius sp.A , CNCC), Ellesmere Island , Lake Hazen, Hazen Camp, 81.5°N 71.2°W, 158 m a.s.l., ‒14 °C m.a.t., 17.vii.1961, leg. D. R GoogleMaps . Oliver .— FINLAND, 1 adult male (as P. pectinatus, ZMUO ), Lake Kankareenjärvi , 60.44°N 22.96°E, 80 m a.s.l., +5 °C m.a.t., 20.iv.2015, leg. L. Paasivirta [Barcode LEFIJ3520-16 ] GoogleMaps ; 2 adult males (as Procladius sp. , ZMUO), Lake Nummijärvi , 60.59°N 23.25°E, 97 m a.s.l., +4 °C m.a.t., 4.v.2015, leg. L. Paasivirta [Barcode LEFIJ3905-16 and LEFIJ3906-16 ] GoogleMaps ; 2 adult males (as Procladius sp. , ZMUO), Lake Iso-Ruostejärvi , 60.69°N 23.80°E, 117 m a.s.l., +4 °C m.a.t., 5.v.2015, leg. L. Paasivirta [Barcode LEFIJ3670-16 and LEFIJ3671-16 ] GoogleMaps .— GREENLAND, 3 adult males (as P. choreus, ZMUC ), Cape Oswald Peninsula , Franz Josef Fjord district, 72.5°N 25.0°W, 10 m a.s.l., ‒7 °C m.a.t., vii‒viii.1934, leg. F.S. Andersen. GoogleMaps — NORWAY, 1 adult male (Holotype of Tanypus frigidus, NHRS ), Bear Island , Mount Misery, 74.42°N 19.20°E, 300 m a.s.l., ‒3 °C m.a.t., 25.viii.1868, leg. A.E. Holmgren GoogleMaps ; 1 adult male (as P. choreus, MTSN ), Svalbard , Progetto, Londonelva 3, 78.58°N 12.04°E, 355 m a.s.l., ‒6 °C m.a.t., 13.viii.1997, leg. L. Marziali GoogleMaps ; 1 adult male ( NTNU), Svalbard , Adventdalen, Todalen below mine cave 5, 78.16°N 15.83°E, 100 m a.s.l., ‒5 °C m.a.t., 26.vii.2005, leg. O. Frengen [Barcode MIDGE069-06 ] GoogleMaps ; 1 adult male ( NTNU), Svalbard , Kapp Linné, Lake Søndre Borgdam, 78.07°N 13.79°E, 35 m a.s.l., ‒5 °C m.a.t., 8.viii.2008, leg. T GoogleMaps . Ekrem and K. Hårsaker [Barcode CHRSV120-08 ] ; 1 adult male ( NTNU), Kautokeino , Lahpoluoppal, lake, 69.21°N 23.76°E, 321 m a.s.l., ‒2 °C m.a.t., 12.vi.2010, leg. T GoogleMaps . Ekrem and E. Stur [Barcode CHRFI033-10 ] ; 1 adult male ( NTNU), Porsanger , Lake Øvrevatn, Skoganvarre, 69.84°N 26.08°E, 76 m a.s.l., 0 °C m.a.t., 16.vi.2010, leg. T GoogleMaps . Ekrem and E. Stur [Barcode CHRFI426-11 ] .— RUSSIA, 1 adult male (as Tanypus signatus, ZISP ), Kotelny Island , River Wosnessenje, 75.16°N 145.15°E, 300 m a.s.l., ‒18 °C m.a.t., 23.vii.1903, leg. M.I. Brussnew. GoogleMaps

Diagnostic characters. Figs. 32 View FIGURES 32‒35 , 83‒85 View FIGURES 83‒85 , key couplet 14. P. frigidus has a medium long gonostylus process with a GspR that overlaps that of eight other species of Procladius in Europe. Of these, P. culiciformis , P. tenebricosus , P. ferrugineus , P. floralis and P. crassinervis are easily separated from P. frigidus by the absence of setae on the median anepisternum and one or more other characters in the key and helpdesk.

It is neither a problem to distinguish P. frigidus from P. lugubris by characters such as gonostylus process divergence (10‒25° versus 25‒45°), front leg tarsi BR (3‒4.5 versus 5.5‒8) and the number of spines of the hind leg tibial comb (10‒14 versus 6‒9).

The GspR of P. frigidus strongly overlaps that of P. pruinosus (0.25‒0.33 versus 0.23‒0.30) and completely that of P. longistilus (0.25‒0.33 versus 0.25‒0.34). P. frigidus can be separated from the other species by a combination of other characters, particularly the number of median anepisternal setae (5‒26 versus 0‒6), antenna AR (2.2‒2.8 versus 1.7‒2.3) and the length of palpomere five divided with its width (8.0‒9.3 versus 9.1‒12.2). P. frigidus is mainly an Arctic, cold-adapted species (mean annual temperature +5 to ‒15 °C), while P. pruinosus mostly lives in warmer temperature conditions (mean annual temperature +18 to ‒1 °C).

P. frigidus has been regarded as a synonym of P. crassinervis for a hundred years ( Edwards 1924) until recently when Stur & Ekrem (2020) reestablished P. frigidus as a valid species name. The adult female and larva have been described. The pupa has not been described. Barcodes of adult males, adult females, a pupa and larvae are available.

Geographical distribution and ecology. As its Latin name implies, P. frigidus is a cold-adapted species. It is in fact the most northerly distributed of all Procladius species in the northern hemisphere, with findings up to latitude 79°N in Svalbard Island of Norway and 82°N in Ellesmere Island of Canada. The southernmost records are from southern Finland at 60°N. Altitude of the 33 sites with quality assured records ranges from about 2 m to about 360 m above sea level. Mean annual temperature extends from + 5 in Finland to ‒18 °C on an Arctic island near the Arctic Ocean coast of Siberian Russia. This is the coldest condition in terms of mean annual temperature known for a species of Procladius and other species of Chironomidae , in fact among the coldest known for any insect species. Noteworthy is that there are at least fifty species of Chironomidae known from sites with mean annual temperature ranging from ‒14 to ‒18 °C.

The northernmost ponds and lakes where the larvae of P. frigidus live can have a complete ice cover lasting for eight to more than ten months a year. Larvae have been found from 0 to 9 m water depth and are able to hibernate in a frozen state in bottom sediments for at least five months. Bottoms of these lakes can be devoid of oxygen and contain poisonous hydrogen sulfide.

The larvae of P. frigidus have been reported to be fast swimmers, even swimming backwards, and to feed on smaller chironomids and crustaceans. The ponds and lakes with larvae are ultraoligotrophic to oligotrophic and mostly free of fish, but some contain Arctic char ( Salvelinus alpinus ).

The development of P. frigidus from the first instar larvae to adult may take three years or more in the coldest lakes with water temperature that rarely exceed +4 °C. They may overwinter as inactive prepupae. As for other Chironomidae of Arctic lakes and ponds, emergence of P. frigidus can take place as soon as cracks in the ice appear in mid-June or as late as early July. Emergence can continue for about three weeks, which is substantially longer than that for most other insect species in these lakes.

Summer weather even at the coldest sites can reach more than +20 °C, so conditions for activity of the adults such as mating and egg-laying can be favourable. Adults have been caught from mid-April to early June in southern Finland and from mid-June to mid-August in colder climate conditions.

Adults of P. frigidus have been found to be common in the diet of snow buntings ( Plectrophenax nivalis ) in Svalbard, Norway, and in southern Greenland. Adults are also known to be food items of other birds such as dunlins and sanderlings ( Calidris alpina and C. alba ).

Countries with records of P. frigidus in Europe are Finland and Norway. It is also present in Canada, Greenland and Russia (Asia).

References. Andersen 1937; Andersen 1946; Edwards 1924; Edwards 1931; Goetghebuer & Lenz 1936a; Henriksen 1939; Hirvenoja 1967; Holmgren 1869; Lindegaard 2015; Lods-Crozet et al. 2007; Lundström 1915; Oliver 1963; Oliver 1968; Paasivirta 2012; Ratnasingham et al. 2024; Roback 1966b; Roback 1971; Saether 2004; Stolz et al. 2023; Stur & Ekrem 2020; Thienemann 1941; Wirta et al. 2015.