Chironomus (Chironomus) bifurcatus Wülker, Martin, Kiknadze, Sublette et Michiels

Saether, Ole A., 2012, The Chironomus group (Diptera: Chironomidae) in Lake Winnipeg, Canada, Zootaxa 3275, pp. 1-19 : 5-8

Chironomus (Chironomus) bifurcatus Wülker, Martin, Kiknadze, Sublette et Michiels

( Figs 3 D–F, 4 A–D, 5, 9)

Chironomus (Chironomus) bifurcatus Wülker, Martin, Kiknadze, Sublette et Michiels, 2009: 36 .

Material examined. Lake Winnipeg light traps: 4 km off Grand Rapids, 7 males, 8.vi. 1969; 0.5 km off George Island, 8 males, 12.vii. 1969; 3 km off Grand Rapids, 14 males, 13.vii. 1969; 10 km off (Sturgeonskin point) Long Point, 16 males, 14.vii. 1969; 3 km off McCreary Island, 15 males, 15.vii. 1969; Gull Harbour, 3 males, 16.vii. 1969; Gimli Government Wharf, 2 males, 24.vii. 1969; Victoria Beach, 2 males, 25.vii. 1969; 3 km off George Island, 51 males, 27.vii. 1969; Grand Rapids Government Wharf, 42 males, 28.vii. 1969; 5 km off Selkirk (Horse) Island, 2 males, 29.vii. 1969; Pine Dock, 34 males, 31.vii. & 2.ix. 1969; 3 km off Grand Rapids, 28 males, 4.ix. 12969; 15 km E off Long Point, 2 males, 6.ix. 1969; McBeth Harbour, 2 males, 7.ix. 1969; Beaver Point, 475 males, 9.vi. – 27.viii. 1971; 20 Mile Creek, 14 males, 28.vii. –1.ix. 1971; Old Fishing Dock, 11563 males, 16.vi.

–18.viii. 1971; Calder's Dock, 8266 males, 9.vi. –8.ix. 1971; Hecla Island, 1580 males, 27.vii. –25.viii. 1971. Emergence traps: Beaver Creek, 10 males, 3.vi. –26.vii. 1971. Rearing specimens: 16 km East Long Point, 1 male, 10.vi. 1969; 24 km SSE Long Point, 2 males, 10.vi. 1969; Saskatchewan River Buoy, 1 male, 13.vii. 1969; NNE of Reindeer Island, 1 male, 15.vii. 1969; NNE of Reindeer Island, 1 male, 27.x. 1969; Centre South basin, 1 male, 31.x. 1969; Outer buoy of Red River, 1 male, 17.iii. 1970; N outer buoy Red River, 17.iii. 1970. South Basin: 281 larvae, 4.vi. –31.x. 1969; Narrows: 8 larvae, 2.ix. –12.x. 1969; North Basin, 121 larvae, 1 pupa, 4.vi. –31.x. 1969.

Normal adult males from Lake Winnipeg have an AR of 3.43–4.05, 3.88 (14); 7–19, 13 (10) sensilla chaetica on p2; and 7–18, 13 (10) sensilla chaetica on p3. The adult females have 88–114, 104 (6) sensilla chaetica on p2; 94–122, 107 (7) sensilla chaetica on p3. 21 % of the males caught in light traps are male intersexes with completely female antenna ( Saether & Galloway 1980 table 3). Some samples, however, have up to 95% intersexes.

The female genitalia of C. bifurcatus from Lake Winnipeg are illustrated by Saether (1977 fig. 81 F–G).

The immatures of C. bifurcatus are illustrated ( Figs 3 D–F, 4 A–D). The pupa drawn, with 6–7 filamentous Lsetae on segment VIII, is the only one which has more than 5 filamentous L-setae. The head capsule lengths of different instars is shown in Fig. 9 . The species, together with C. entis , completely dominate other Chironomus species in the lake.

Remarks. Although the species morphologically appear inseparable from C. decorus Johannsen, Johannsen (1905) notes that “this species is common in ... ponds and ditches …”. C. decorus does not occur in lakes, but some of the described members of the C. decorus -group do. Butler et al. (1995) note that C. decorus -group sp. 1, now C. bifurcatus ( Wülker et al. 2009) , is common in the profundal of North Dakota lakes. Their C. decorus -group sp. 2, while common in lakes from Lake Waskesui to Mississippi, tends to be in shallower areas. Other described members of the C. decorus -group are C. blaylocki Wülker, Martin, Kiknadze, Sublette et Michiels , and the two marine species described by Martin et al. (2010). Comparison of the present material to the description of C. bifurcatus supports show that the present species can be identified as C. bifurcatus .

Distribution and ecology. The C. decorus group to which C. bifurcatus belongs is known from all over North America ( Townes 1945: 122, Oliver et al. 1990: 42). However, according to Sublette & Sublette (1974) and Martin (2012) several unnnamed species, are included in the records. C. bifurcatus appears in North America to have taken the ecological niche occupied by C. anthracinus in Europe, i.e. it is a character form of the profundal zone of moderately eutrophic lakes ( Saether 1975: 3127, 3131). It is found in Quebec, Ontario, Manitoba, Massachusetts, Wisconsin, Michigan, Minnesota and Kansas ( Martin 2012).

In Lake Winnipeg the species is the dominant Chironomus species in the benthos of the South Basin ( Figs 1 , 5 ). Most imagines were caught in the light traps from 1971 ( Fig. 5 ), but these were all set in the Narrows. There apparently are two generations a year.

Figures

FIGURE 1. Distribution of Chironomus spp. in the benthic samples of Lake Winnipeg.

FIGURE 3. Chironomus (Chironomus) spp, pupa. A, D: frontal apotome. B, E, G: tergites. C, F, H: anal spur. A – C: Chironomus (Chironomus) entis Shobanov. D – F: Chironomus (C.) bifurcatus Wülker, Martin, Kiknadze, Sublette et Michiels. G, H: Chironomus sp.

FIGURE 5. Chironomus (Chironomus) bifurcatus Wülker, Martin, Kiknadze, Sublette et Michiels. Numbers of adults caught in light traps and emergence traps in 1969 and 1971, and numbers of immatures in benthic samples from June to November 1969 and in March 1970. (LT = light traps, ET = emergence traps, short vertical lines = 1 – 25 specimens, second shortest lines = 26 – 50 specimens, medium long lines = 50 – 200 specimens; second longest vertical lines = 201 – 400 specimens, longest vertical lines = more than 400 specimens, 1 = first instar larvae, 2 = second instar larvae, 3 = third instar larvae, 4 = fourth instar larvae, P = pupae.)

FIGURE 9. Head capsule lengths of different instars of Chironomus (Chironomus) entis Shobanov and Chironomus bifurcatus Wülker, Martin, Kiknadze, Sublette et Michiels in Lake Winnipeg.