Cryptochironomus ramus Mason

Saether, Ole A., 2009, Cryptochironomus Kieffer from Lake Winnipeg, Canada, with a review of Nearctic species (Diptera: Chironomidae), Zootaxa 2208, pp. 1-24 : 10-14

Cryptochironomus ramus Mason

( Fig. 4 A, 5)

Cryptochironomus sp. n. B Chang et al. 1993. Cryptochironomus sp. n. A Chang et al. 1994.

Material examined. CANADA: Manitoba, Lake Winnipeg records: Victoria Beach, 53 males, 9. & 25.vii. 1969; Pine Dock, 38 males, 10.vii.–2.ix.1969; 0.5 km off George Island, 3 males, 11.vii. 1969; 3 km off Grand Rapids, 1 male, 13.vii. 1969; 10 km off (Sturgeonskin) Long Point, 67 males, 14.vii. 1969; 3 km off McCreary Island, 462 males, 15.vii. 1969; Gull Harbour, 16 males, 16.vii. 1969; 3 km off George Island, 11 males, 27.vii.1969; Grand Rapids Government Wharf, 34 males, 28.vii. 1969; 5 km of Selkirk (Horse) Island, 6 males, 29.vii. 1969; McBeth Harbour, 7 males, 7.ix. 1969; Beaver Point, 9 males, 30.vi.–19.viii. 1971; 20 Mile Creek, 5 males, 22.vii.–1.ix. 1971; Old Fishing Dock, 226 males, 29.vi.–18.viii. 1971; Calder’s Dock, 33 males, 28.vii.–31.viii. 1971; Hecla Island, 21 males, 27.vii.–25.viii. 1971; Beaver Creek, 5 males, 1 pupal exuviae, 15.vi.–29.vii 1971; 16 km east Long Point, 3 males, 10.vi. & 15.vii. 1969; South Basin, 43 larvae, 4.vi.–31.x. 1969; Narrows, 36 larvae, 4. vi.–31.x. 1969; North Basin, 152 larvae, 1 pupa, 4.vi.–31.x. 1969.

The male imagines of C. ramus from Lake Winnipeg are characterized by a wing length of 3.01–3.50 mm, an AR of 2.93–3.40, LR1 of 1.40–1.55, absence of frontal tubercles, and hypopygium of C. fulvus type. The pupa has extremely long cephalic tubercles (about 1.37 mm) with a very long (about 0.97 mm) main branch, is about 7.0 mm long, and has about 65 filaments in fringe of anal lobe. The presumed fourth instar larvae have head capsule length of 0.52–0.72 mm, postmentum length of 220–248 µm, ventromental plates 2.96–3.24 times as long as wide, AR of 1.4–1.7, and apical tooth of mandible 0.21–0.26 times as long as mandible.

Male imago (n = 9–11, except when otherwise stated)

Total length 6.08–7.35, 6.80 mm. Wing length 3.01–3.50, 3.24 mm. Total length/wing length 1.96–2.19, 2.09. Wing length/length of profemur 2.52–2.64, 2.56.

Head. AR 2.93–3.40, 3.20 (46). Temporals 28–45, 35. Clypeus with 19–29, 23 setae. Tentorium 183–233, 204 long. Stipes 183–230, 210 long. Frontal tubercles completely absent. Palp lengths (microns): 48–67, 57; 72–100, 88; 183–216, 198; 186–213, 192; 266–310, 282.

Thorax. Antepronotum with 9–15, 11 setae. Dorsocentrals 17–27, 21; acrostichals 18–25, 21; prealars 6– 9, 7; parascutellar 1. Scutellum with 26–53, 34 (57) setae.

Wing. VR 1.07–1.11, 1.09. Brachiolum with 2–5, 4 setae; R with 22–31, 26; R1 with 13–21, 16; R4+5 with 15–34, 19 setae. Squama with 16–30, 22 (48) setae.

Legs. Sensilla chaeticae 1–5, 3 (49) on mid leg; 0–5, 2 (48) on hind leg. Lengths and proportions of legs as in Table 1.

TABLE 1. Lengths (in μm) and proportions of legs of Cryptochironomus ramus Mason , Male. fe ti ta1 ta2

p1 1177–1378, 1266 992–1126, 1063 1471–1698, 1598 672–756, 724

p2 1143–1311, 1252 1076–1244, 1173 664–756, 716 313–384, 347

p3 1126–1462, 1354 1446–1673, 1560 992–1168, 1063 462–555, 507 ta3 ta4 ta5 LR

p1 578–664, 622 435–510, 480 184–221, 202 1.40–1.55, 1.51(49)

p2 238–292, 277 153–186, 173 113–150, 134 0.60–0.62, 0.62

p3 381–469, 435 200–272, 240 130–63, 151 0.66–0.71, 0.68

BV SV BR

p1 1.88–1.98, 1.94 1.43–1.51,1.46 2.88–4.93, 3.21

p2 3.24–3.63, 3.36 3.28–3.47,3.37 3.31–5.00, 3.65

p3 2.91–3.20, 2.99 2.51–2.84,2.74 3.57–5.21, 4.25

Hypopygium ( Fig. 4 A). T IX with 28–41, 34 setae; laterosternites IX each with 4–7, 5 setae. Phallapodeme 193–236, 208 µm long. Transverse sternapodeme 92–120, 110 µm long. Gonocoxite 223–260, 24 µm; gonostylus 210–250, 233 µm. HR 0.96–1.11, 1.04; HV 2.75–3.08, 2.91. Pupa (n = 1)

Total length 7.00 mm.

Cephalothorax. Cephalic tubercles ( Fig. 5 B) fused at base, 1368 µm long, 400 µm wide at base; main branch 969 µm long, 215 µm wide for the first 172 µm, 98 µm wide below first lateral branch, 20 µm wide below apical branch; lateral branch 150 µm long, 46 µm wide at base; apical branch 22 µm long, 14 µm wide; frontal seta 84 µm long.

Abdomen ( Fig. 5 A). Tergites and sternites not reticulated. Shagreen and chaetotaxy as illustrated. Caudal margin of T II with 44 hooklets to each side of 156 µm wide mesa] interruption. Pedes spurii A present on S IV–VII, longest spinules 22 µm on IV, 10–11 µm on V–VII. Caudal margins of T II–VIII respectively with the following numbers of spines (lengths in parentheses): indication (7 µm), 53 (12 µm), 54 (14 µm), 57 (14 µm), 42 (22 µm), 31 (24 µm), 24 (12 µm). Caudal margins of S II–VIII respectively with the following numbers of spines (lengths in parentheses): 22 (8 µm), 26 (8 µm), 23 (10 µm), 29 (14 µm), 27 (21 µm), 26 (30 µm), 33 (23 µm). Caudomedian projection of anal lobe 206 µm long, 130 µm wide, with 68 µm long, 14 µm wide branches. Genital sac of male with 20 µm long, 20 µm wide apical point. Fringe of anal lobe with 65 filaments.

Fourth instar larva (n = 8–10, except when otherwise stated, tentatively associated)

Total length 6.48–10.63, 8.39 mm. Head capsule length 0.52–0.66, 0.60 mm (217).

Head. Antenna as in Fig. 5 C. Lengths of antennal segments (in µm): 78–90, 82; 24–28, 26; 20–22, 21; 3– 4, 4; 3–4, 4. AR 1.42–1.67, 1.54. Basal antennal segment 31–36, 33 µm wide; 3.00–3.52,3.25 times as long as second segment; ring organ 48–64, 56 µm from base. Preapical blade of second segment 30–37, 32 µm (5) long; apical style 10–11, 11 µm (5) long. Labrum ( Fig. 5 D) with 30–38, 34 µm (7) long labral sensilla; SI 30– 40, 34 µm (6); SII 50–60, 56 µm (6) long. Premandible ( Fig. 5 E) 136–146, 141 µm long. Mandible ( Fig. 5 F) 180–218, 197 µm long; with 42–52, 46 µm long apical tooth which is 0.21–0.26, 0.241, times as long as mandible. Basal segment of maxillary palp 60–78, 70 µm long; 20–27, 25 µm wide. Median tooth of mentum ( Fig. 5 G), including darker lateral accessory teeth 58–63, 61 µm wide. Ventromental plate 160–194, 1$9 µm wide; 54–64, 58 µm long; 2.96–3.24, 3.10 times as wide as long. Postmentum 220–248, 234 µm long. Gula and postoccipital margin pale.

Abdomen. Procercus 36–50, 42 µm high; 36–60, 46 µm wide; with 564–785, 692 µm long anal setae. Supraanal seta 405–527, 446 µm (6); Supraanal seta/anal setae 0.52–0.72, 0.62(6). Anal tubules triangular 130–180, 160 µm long; 68–106, 79 µm wide at base. Posterior parapods 393–466, 424 µm long.

Third instar larva

Head capsule length 0.32–0.40, 0.36 mm (162) (See Fig. 9 ).

Second instar larva

Head capsule length 0.19–0.24 mm (3) (See Fig. 9 ).

Remarks. The specimens from Lake Winnipeg are considerably smaller than those described by Mason (wing length 3.01–3.50 as opposed to 4.05–4.75 mm, pupa 7.0 mm as opposed to 8.0– 9.2 mm). The variety described below is even smaller. However, the very characteristic cephalic tubercles assure the conspecificity. Perhaps the difference is caused by more generations in Lake Winnipeg and just one in Lake Tobin. The antennal ratios also differ with AR 2.93–3.40 in Lake Winnipeg versus 2.64–2.91 in Lake Tobin. Another explanation is that the presence of several species of the genus Cryptochironomus with similar ecology cause the different larvae to segregate in size in order to share the resources. Thus the larval size of C. ramus is depressed by the larger C. stylifera (Fig. 00). A similar size segregation takes place also among the larvae of Procladius Skuse where seven species are found in Lake Winnipeg, five of them common.

Distribution and ecology. Mason (1983: 412) collected larvae of C. ramus from pebble, sand and clay substrates in water 0.5–2.0 m deep in Lake Tobin, Saskatchewan.

Figures

FIGURE 4. Cryptochironomus ramus Mason (A) and Cryptochironomus imitans sp. n. (B – D), imagines. A, C — male hypopygium; B — frontal tubercles; D — female genitalia.

FIGURE 5. Cryptochironomus ramus Mason, pupa (A, B) and larva (C – G). A — tergites; B — cephalic tubercles; C - antenna; D — labrum and epipharynx; E — premandible; F — mandible; G — mentum.

FIGURE 9. Head capsule lengths of the four most common species of Cryptochironomus Kieffer in Lake Winnipeg.