Robackia pilicauda Saether

Kobayashi, Tadashi, 2007, Kloosia Kruseman, Chernovskiia Saether, Robackia Saether, and Saetheria Jackson (Chironomidae: Chironominae) in Japan, Zootaxa 1527, pp. 1-15 : 6-9

Robackia pilicauda Saether

( Figs. 4–5 )

Robackia pilicauda Saether, 1977: 129 .

Material examined. JAPAN: Gifu Prefecture, Nagara River, 2.7–3.5 km from mouth, 29 males, 20.v.2004, S. Kondo ( CHI 36: 21–36, CHI 36: 38–55); Yamaguchi Prefecture, Iwakuni City, Nishiki River, 5 males, 28.v.1993, T. Kobayashi ( CHI 36: 51–55); Gifu Prefecture, Kiso River, 1 larva, 1997, N. Kitagawa (Kitagawa’s code 8211); Hiroshima Prefecture, Kose River, 2 larvae, 24.vi.2002, N. Shimura ( CHI 36:56, 57); Fukushima Prefecture, Surigami River, 2 larvae, 1.vii.1996, T. Kishimoto ( CHI 43:48, 49); Mie Prefecture, Kumano River, 1 larva, 2005, N. Kitagawa (Kitagawa’s code 9539).

Male [Characteristics of R. claviger and R. pilicauda according to Saether (1977: 125, 129) in brackets].

Total length 2.70–3.80, 3.04 (34) mm; [3.15–4.07, 3.60 mm in R. claviger ; 2.50–3.03, 2.74 mm in R. pilicauda ]. Coloration light brown, vittae darker.

Head. AR = 2.10–2.69, 2.33 (21); [2.04–2.40, 2.19 in R. claviger ; 1.80–2.10, 1.92 in R. pilicauda ]. Temporal setae 10–12, 11 (9); [13–17, 14 in R. claviger ; 12–16, 13 in R. pilicauda ]. Clypeus with 10–12, 11 (5) setae; [8–14, 12 in R. claviger ; 9–14, 12 in R. pilicauda ]. Tentorium ( Fig. 4 A) rather thick, 100 μm long, 35 μm wide. Length (in μm) of palpomeres 2–5: 20 (1); 125–150 (2); 110–125, 120 (4); 150–160, 153 (4).

Thorax. Antepronotals absent. Acrostichals 6–13, 10 (9); [8–10, 9 in R. claviger ; 5–10, 7 in R. pilicauda ], biserial. Dorsocentrals 7–12, 10 (6); [6–8, 7 in R. claviger ; 5–8, 6 in R. pilicauda ], uniserial. Prealars 4–5, 5 (9); [4–5, 4 in R. claviger ; 3–5, 4 in R. pilicauda ], uniserial. Scutellum with 7–10, 8 (9); [8–12, 9 in R. claviger ; 5–8, 7 in R. pilicauda ], transversely uniserial.

Wing ( Fig. 4 B). Length 1.70–2.15, 1.86 (31) mm; [1.57–1.10, 1.82 mm [sic.] in R. claviger ; 1.20–1.46, 1.34 mm in R. pilicauda ]. VR 0.61. Costal extension absent. R2+3 running close to R1. Squama with 9–14, 11 (7) setae; [9–12, 11 in R. claviger ; 4–8, 6 in R. pilicauda ].

Legs. Fore tibial scale and mid- and hind tibial combs as in Figures 4 C–E. Lengths and proportions of legs as in Table 2 .

Hypopygium ( Fig. 4 F). With 0–8, 3 (8) setae adjacent to anal point. Anal point more or less parallel-sided, apex rounded, with 3–12, 8 (8) weak setae [10–12 weak setae in R. claviger and R. pilicauda ]. Anal point 0.67–0.88, 0.77 (7) times as long as phallapodeme [0.65–0.87 in R. claviger , 1.03–1.14 in R. pilicauda ]. Superior volsella variable ( Fig. 4 G), generally elongate, without microtrichia, with 2 setae apically. Inferior volsella pad-like, covered with microtrichia, without setae. Gonostylus clavate, widest near apex.

Larva. Head. Antenna ( Figs. 5 C, F) with 7 segments. Mandible ( Figs. 5 B, E) with inner teeth and seta interna. Mentum ( Figs. 5 A, D) with 14 teeth; ventromental plates about as wide as long, with strong striation.

Remarks. Saether (1977) diagnosed R. demeijerei on the completely bare anal point and an AR of about 1.5. The other two species have some minute spine-like setae on the anal point and the AR of R. claviger is c. 2.19, of R. pilicauda c. 1.92. The anal point of the present specimens apparently has some spine-like setae, and the AR is 2.33. Therefore R. demeijerei should be left out of consideration. However, according to Martin Spies (pers. comm. to Ole A. Saether) the description of the male of R. demeijerei by Lehmann (1970: 140– 142) is inaccurate. There are at least some weak distal setae on the anal point, but apparently fewer than in R. claviger and R. pilicauda . In some characters, like the wing length, the antennal ratio, and the ratio length of anal point / length of phallapodeme, the present specimens are closer to R. claviger than to R. pilicauda . However, according to Saether (pers. comm.), the shape of the anal point is the most important character separating the two species. Based on Saether (1977) R. claviger has a spatulate anal point, while the anal point in R. pilicauda is more parallel-sided. Thus, the Japanese specimens should be assigned to R. pilicauda .

All the Japanese larvae studied have a mentum with 14 equal teeth, consistent with the description of R. claviger by Saether (1977: 128). The median teeth of mentum are not slightly wider than the lateral teeth as mentioned by Saether (1977: 124), and the teeth row is almost straight ( Figs. 5 A, D). In two of the Japanese specimens (CHI 36:56, CHI 36:57), the proximal teeth of the mandible ( Fig. 5 B) are conspicuous enlarged, in agreement with the description of R. claviger ; in the remaining four specimens (Kitagawa’s code 8211, 9539; CHI 43:48, CHI 43:49), the proximal teeth are less conspicuous ( Fig. 5 E). However, on the whole all the Japanese larvae are similar, and the former (CHI 36:56, CHI 36:57) are considered to be in a later larval stage than the latter.

In most characters, the larvae from Japan confirm to the description of R. claviger by Saether (1977). However, they differ in having the median teeth of mentum subequal, and not wider and shorter than the lateral teeth as in R. claviger . Further, the second-most outer tooth is distinctly smaller than the remaining teeth. The larva of R. pilicauda is not described, and Epler (2001) regards R. pilicauda as a possible junior synonym of R. claviger . Although the male of R. pilicauda can not be separated from that of R. claviger with certainty, the present larvae apparently refute this possibility.

Figures

FIGURE 4. Robackia pilicauda (Saether, 1977), male. A, tentorium. B, wing. C, tibial scale of foreleg. D, tibial combs of midleg. E, tibial combs of hind leg. F, hypopygium. G, variation in superior volsella.

FIGURE 5. Robackia pilicauda (Saether, 1977), larvae, A & D, mentum and ventromental plate. B & E, mandibles. C & F, antennae.

Tables

TABLE 2. Lengths (in μm) and proportions of legs of Robackia pilicauda Saether, 1977, male, from Japan.

	fe	ti	ta1	ta2
p1	640–690 (3)	490–550, 518 (6)	730–850, 780 (4)	440–500 (3)
p2	610–770, 688 (4)	600–740, 650 (4)	310–360, 335 (4)	190–225, 206 (4)
p3	650–860 (2)	760–950, 854 (5)	500–650, 566 (5)	300–350, 314 (5)