Saetheria tylus (Townes)

Kobayashi, Tadashi, 2007, Kloosia Kruseman, Chernovskiia Saether, Robackia Saether, and Saetheria Jackson (Chironomidae: Chironominae) in Japan, Zootaxa 1527, pp. 1-15 : 10-13

Saetheria tylus (Townes)

( Figs. 6–7 )

Saetheria tylus ( Townes, 1945: 150–151).

Paracladopelma nagaraelongata Sasa, 1989: 65 ; Sasa and Okazawa (1992: 43); Inoue et al. (2004: 31); Kondo et al. (2005: 52). Syn. n.

Paracladopelma kisopediformis Sasa et Kondo, 1993: 98 . Syn. n.

Parachironomus taishoabeus Sasa et Tanaka, 2001: 46 . Syn. n.

Material examined. JAPAN: Gifu Prefecture, Gifu City, Minato-machi, Nagara River, holotype male of Paracladopelma nagaraelongata Sasa , 25.x. 1988, M. Sasa (Type No. 170: 42); Gifu Prefecture, middle reaches of Kiso River, holotype male of Paracladopelma kisopediformis Sasa et Kondo , 15.xi. 1988, M. Sasa (Type No. 220: 70); Gunma Prefecture, Tone River, Taisho Bridge, holotype male of Parachironomus taishoabeus Sasa et Tanaka , 13.ix. 1999, N. Tanaka (Type No. 392: 81); Aichi Prefecture, Yahagi River, Toyoda Bridge, 1 male, x. 2003, S. Kondo ( CHI 19: 56); Gifu Prefecture, Kiso River, Oki, 1 male, 28.v. 2001, T. Kobayashi ( CHI 27: 24); Gifu Prefecture, Nagara River, Nagaraohashi Bridge, 1 male, 29.v. 2001, T. Kobayashi ( CHI 29: 77); Gifu Prefecture, Nagara River, Horitsu, 2 males, 2.x. 2001, T. Kobayashi ( CHI 29: 79, CHI 29: 80); Nagasaki Prefecture, Todoroki Valley, 2 males, 25.x. 2000, H. Suzuki; Niigata Prefecture, Shibumi River, 3 larvae, 3.viii. 2005, N. Shimura ( CHI 43: 45–47); Shiga Prefecture, Lake Biwa, 2 larvae, vi. 1997, N. Kitagawa (as S. sp. SA, Kitagawa’s code B021– 1, B021– 2); Hokkaido, Kushiro River, 1 larva, 1993, N. Kitagawa (as S. sp. SB, Kitagawa’s code 8721); Gifu Prefecture, Nakatsu River, tributary to Kiso River, 1 larva, xi. 2000, N. Kitagawa (as S. sp. SD, Kitagawa’s code 8547); Okayama Prefecture, Takahari River, 1 larva, 2003, N. Kitagawa (as S. sp. SE, Kitagawa’s code 9113); Nagano Prefecture, Nakatsu River, tributary to Shinano River, 1 larva, 2004, N. Kitagawa (as S. sp. SF, Kitagawa’s code 9306); Nagano Prefecture, Nakabusa River, tributary to Sai River, 1 larva, 2004, N. Kitagawa (as S. sp. SG, Kitagawa’s code 9332); Gifu prefecture, Itadori River, tributary to Nagara River, 1 larva, 17.viii. 2004, N. Kitagawa (as S. sp. SH, Kitagawa’s code 9603).

Male (n = 4–8)

Total length 2.3–2.8, 2.6 mm.

Head ( Fig. 6 A). Frontal tubercles clearly present, but small, c. 8 μm long, 7 μm wide. Antenna with 11 flagellomeres; AR 1.71 –2.00, 1.84. Temporals 10 –14, 12. Clypeus with 10 –17, 12 setae. Tentorium c. 120 μm long, 30 μm wide. Length (in μm) of palpomeres 2–5: 25 –40, 31; 95–110, 101; 100–115, 106, 155 – 180, 167. Thorax. Antepronotals 2 –3, 3; acrostichals 7 –11, 9; dorsocentrals 8 –9, 9; prealars 2 –3, 3. Scutellum with 5 – 10, 8.

Wing ( Fig. 6 B). Length 1.34–1.60, 1.48 mm. Brachiolum with 0–1 seta. Squama with 2 –3, 3 setae.

Legs. Fore tibial scale and mid- and hind tibial combs as in Figures 6 C –E. Pulvilli well developed. Lengths (in μm) and proportions of legs as in Table 3.

Hypopygium ( Fig. 6 F). Anal tergite bands partially fused, Y-shaped. Anal point bare, with rounded apex. Superior volsella bilobed, each lobe with single strong seta. Inferior volsella low, extending along inner margin of gonocoxite, with microtrichia, without setae. Gonostylus gently curved.

Larva (Kitagawa’s code B021, S. sp. SA).

Head. Antenna ( Fig. 7 A) 5 segmented, ring organ in proximal 1 / 4 of basal segment, blade apically on 2 nd segment, extending to near apex. SI seta-like; SII long, broadly blade-like ( Fig. 7 B). Premandible with 4 teeth distally, brush lacking ( Fig. 7 C). Mandible ( Fig. 7 D) with apical tooth and 3 inner teeth; seta subdentalis moderately long, blade-like; seta interna consisting of 4 long serrated lamellae; pecten mandibularis consisting of 3 long lamellae. Mentum ( Fig. 7 E) with narrow median tooth and 6 pairs of lateral teeth; ventromental plates widely separated medially, distinctly striated, about as wide as mentum.

Remarks. The adults of Saetheria tylus differ from S. reissi by the presence of frontal tubercles and in the shape of the superior volsella, which is bilobed in S. tylu s, while it is roughly triangular in S. reissi . The Japanese specimens have small, but distinct frontal tubercles and a bilobed superior volsella, and are thus allotted to S. tylus .

The Japanese Saetheria larvae described by Kitagawa can be split into three groups, mainly based on the morphology of mentum and the ventromental plate. Group A ( Figs. 7 A –E): S. sp. SA (Kitagawa 1977 b: 37, Fig. 12), S. sp. SB ( Kitagawa 1998: 187, Fig. 11), S. sp. SD ( Kitagawa 2002: 34, Fig. 18), and S. sp. SF ( Kitagawa 2004: 24, Fig. 9). Group B ( Figs. 7 F –I): S. sp. SE ( Kitagawa 2003: 29, Fig. 11) and S. sp. SH ( Kitagawa 2005: 36, Fig. 15). Group C ( Figs. 7 J –M): S. sp. SG ( Kitagawa 2004: 25, Fig. 10). The three larvae from Shibumi River ( CHI 43: 45–47) collected by N. Shimura apparently belong to Group B.

Group A resembles the larva of S. tylus (see Jackson 1977: 1354, Fig. 31), having a dome-shaped median tooth. According to Jackson (1977: 1353) the larval antenna of S. tylus is 6 segmented. However, according to Kitagawa (1997 b: 37, 2002: 34, 2004: 24) the antennae of S. sp. SA, S. sp. SD, and S. sp. SF appear to be 5 segmented, while the antenna of S. sp. SB ( Kitagawa 1998: 187) is 6 segmented. Group B resembles S. hirta described by Saether (1983). Group C has a broad ventromental plate and shows similarities to Jackson’s (1977) S. sp. 1 and Wang et al. ’s (1991) S. sp. However, the identity of the various larvae can not be decided with certainty as none of the larvae have associated males.

Figures

FIGURE 6. Saetheria tylus (Townes, 1945), male. A – C: Specimen CHI 36: 56. A, head. B, wing. C, tibial scale of foreleg. D – F: Specimen CHI 43: 48. D, tibial combs of midleg. E, tibial combs of hind leg. F, hypopygium.

FIGURE 7. Saetheria spp., larvae. A – E: Saetheria tylus (Townes, 1945), larva. A, antenna. B, SI and SII. C, premandible. D, mandible. E, mentum and ventromental plate. F – I: Saetheria sp. SE, (redrawn from Kitagawa 2003, Fig. 11). F, antenna. G, labrum and premandible. H, mandible. I, mentum and ventromental plate. J – M: Saetheria sp. SG, (redrawn from Kitagawa 2004, Fig. 10). J, antenna. K, labrum and premandible. L, mandible. M, mentum and ventromental plate.

Tables

TABLE 3. Lengths (in μm) and proportions of legs of Saetheria tylus (Townes, 1945), male, from Japan.

p1
p2
p3