Chironomus dilutus Shobanov, Kiknadze et Butler

Saether, Ole A., 2012, The Chironomus group (Diptera: Chironomidae) in Lake Winnipeg, Canada, Zootaxa 3275, pp. 1-19 : 8-9

Chironomus dilutus Shobanov, Kiknadze et Butler

( Fig. 2 A)

Chironomus (Camptochironomus) dilutus Shobanov, Kiknadze et Butler, 1999: 315 . Chironomus (Camptochironomus) tentans auct. nec Fabricius, 1805: 38.

? Chironomus (Camptochironomus) tentans var. pallidivittatus Malloch, 1915: 445 , not sensu Edwards 1929, see remarks under next species.

Material examined. CANADA, Manitoba, Winnipeg, Freshwater Institute Laboratory Culture, 2 females, 15.i. 1973, J.F. Flannagan; Saskatchewan, LeRoy, 2 females, 7.vi. 1967, A.L. Hamilton. Lake Winnipeg light traps: 3 km off Grand Rapids, 3 males, 13.vi. 1969; 10 km off (Sturgeonskin point) Long Point, 1 male, 14.vi. 1969; 3 km off McCreary Island, 1 male, 15.vi. 1969; Victoria Beach, 1 male, 25.vi. 1969; Grand Rapids Government Wharf, 10 males, 28.vi. 1969; 5 km off Selkirk (Horse) Island, 2 males, 29.vi. 1969; McBeth Harbour, 19 males, 30.vi. 1969.

Normal non-parasitized males from Lake Winnipeg have a wing length of 4.07–5.16, 4.61 mm (10); an AR of 3.00–3.86, 3.55 (14); 20–38, 29 (10) sensilla chaetica on ta1 of p2; and 20–43, 25 (10) sensilla chaetica on ta1 of p3. The females have 170–220 (3) sensilla chaetica on p2, 160–250 (3) sensilla chaetica on p3. The male hypopygium and antenna are illustrated in Saether & Galloway gynandromorph, the others caused by mermithid infection ( Saether & Galloway 1980 fig. 7A, D, as C. tentans ) while the female genitalia are illustrated by Saether (1977 fig.

82A–C). Eight of 25 males were intersexes, one a probable gynandromorph, the others caused by mermithid infections ( Saether & Galloway 1980).

Remarks. It is now realized that Townes (1945) was correct in not recognizing Camptochironomus Malloch as a separate subgenus. Martin (2012) use the name camptochironomus-cytocomplex for species previously placed in the subgenus.

According to Shobanov et al. (1999) Nearctic records of C. tentans Fabricius belong to C. dilutus Shobanov, Kiknadze & Butler , but see Spies & Saether (2004) and remarks under C. pallidivittatus sensu Edwards. According to Martin (2012) there are an eastern race and a western race to which the Lake Winnipeg population belong. C. pallidivittatus is a senior synonym of C. dilutus if reexamination of the type not can show that there is no possibility for it to belong to another species such as the Nearctic C. tentans presently found only in Alaska. If such a possibility exists C. pallidivittatus could be declared a nomen dubium.

Shobanov et al. (1999: 317) gives the number of sensilla chaeticae as near 80. If they mean ta1 of mid and hind leg combined the number is in accordance with the present specimens.

Hein & Schmulbach (1971) found hybridization between C. dilutus (as tentans ) and C. pallidivittatus sensu Edwards. Hybridization appears also to be present in the Lake Winnipeg material ( Fig. 2 C, D). However, mermithid infections are common in Lake Winnipeg and although most specimens are more severely affected ( Saether & Galloway 1980) the illustrated hypopygia could also be caused by more slight changes. caused by parasitazion.

Distribution and ecology. C. dilutus is known from lakes, ponds, puddles and brackish waters across the northern U.S. and Canada ( Townes 1945: 135 as C. tentans, Shobanov et al. 1999: 315 , Martin 2012). C. dilutus appears to occupy the same habitats as C. tentans preferring shallow stagnant waters where the bottom is covered by abundant organic detritus. The larvae are euryoxybiontic and thrive where organic pollution is high ( Townes 1945: 126, 136).

Figures

FIGURE 2. Chironomus spp., hypopygium A: C. dilutus Shobanov, Kiknadze et Butler. B: C. pallidivittatus Malloch sensu Edwards. C – D: Probable hybrids.