Rheotanytarsus lamellatus Reiss

Tejerina, Eva Gabriela & Paggi, Analía Constancia, 2009, A redescription of Rheotanytarsus lamellatus Reiss in all stages (Diptera: Chironomidae) and new records from Argentina, Zootaxa 2315, pp. 31-38 : 32-36

Rheotanytarsus lamellatus Reiss

Rheotanytarsus lamellatus Reiss, 1972: 67

Material examined. Associated pharate adults and pupae with larval exuviae attached in their tubes. ARGENTINA: 4 male and 2 adult females, Tucuman, El Siambón stream, 26° 45' 12.9'' S, 65° 27' 14'' W, 1040 m a.s.l., 3.III.2009; 4 males, 4 males Jujuy, P.N. Calilegua, Yuto stream, 23º 38' 40'' S, 64º 32' 21'' W, 505 m a.s.l., 7.XI.2006; 5 pupae and 6 larvae, La Hoyada, San Miguel stream, 26º 41' 07.7'' S, 65º 31' 09.9'' W, 1300 m a.s.l., 12.IX.2006; 39 larvae, Rio Grande stream, 26° 46' 10'' S, 65° 28' 20.4'' W, 925 m a.s.l., 21.III.2007; 10 pupae, idem except date, 13.IX.2006; 27 pupae and 4524 larvae, San Javier stream, 26º 46' S, 65º 23' W, 860 m a.s.l, 21.III.2007; 23 larvae, idem except date, 13.IX.2006; 284 larvae, Potrero de las Tablas stream, 26º 51' 18.8'' S, 65º 25' 55.5'' W, 680 m a.s.l., 13.IX.2006; 61 larvae, idem except date, 21.III.2007. E. Tejerina coll. Deposited in IML.

Description. Adult male (n = 4 except when otherwise stated)

Coloration: head light brown; thorax with light brown patches anteriorly and laterally on scutum, postnotum and scutellum; abdomen and legs light brown.

Total length 1780–2070 (1925), abdomen length 1220–1370 (1290), thorax length 560–700 (645), wing length 1220–1475 (1314). Total length/wing length 1.40–1.46 (1.42). Wing length/length of profemur 1.96– 2.14 (2.05).

Head. Antenna 552–764 (657) long with 13 flagellomeres; AR 0.45–0.87 (0.63) ( Fig. 1 ). Temporal setae 5–6. Clypeus with 16 setae. Length of palpomeres: 30–32 (31); 28–40 (34); 76–30 (53); 88–90 (89); 172 (n = 2).

Thorax chaetotaxy (n = 1). Dc 11, Ac 16, Scts 10.

Wing ( Fig. 2 ). Length/width 2.92. VR 1.4–1.6 (1.5). Wing setae: brachiolum with 1 seta; Sc bare; R with 18; R1 with 22; R4+5 with 53; M bare; RM bare; M1+2 with 42; M3+4 with 28; Cu with 28; Cu1 with 35; PCu with 56; An with 26 setae (n = 1).

Legs. Fore tibia with spur 35 µm long; 2 spurs of mid tibial combs unequal in size: 30 and 25 long; 2 spurs of hind tibial combs subequal in size: c. 25 long. Length and ratios of leg segments in Table 1.

Hypopygium ( Fig. 3 ). Anal tergite with separated V-shaped bands and 8–10 (9) median setae. Anal point 35–40 (37) long. Crest well developed, open and V-shaped with 4–5 setae arranged in a row between anal tergite bands and anal point.

Gonocoxite 124–148 (136) long; gonostylus 84–104 (94) long.

Inferior volsella cylindrical, 56–64 (60) long, with microtrichia and 10 setae apically. Superior volsella 32 (32) long; 18–22 (20) wide, oval, with 6 dorsal setae in addition to 2 marginal. Median volsella ( Fig. 4 ), stem 28 long (n = 2), with lamelliform setae fused into plate.

Transverse sternapodeme 22 long; lateral sternapodeme 78 long; phallapodeme 50 long (n = 1) ( Fig. 5 ). HR 0.67–0.70 (0.68); HV= 1.99–2.12 (2.05) (n = 2).

Adult female (n = 2 except when otherwise stated)

General color as in male. Total length 1606–1672 (1639), abdomen length 968, thorax length 645–704 (675); wing length 1348–1652 (1500).

Head. Antenna with 6 flagellomeres, 276 long; AR 0.64 (n =1) ( Fig. 6 ). Temporal setae 4. Clypeus with 18 setae. Palpomeres length: 35–32 (34); 30–48 (39); 75–80 (78); 85–104 (95); 165–176 (171).

Thorax chaetotaxy. Scts 6, Ac 15, Dc 12 (n = 1).

fe ti ta1 ta2 ta3 ta4 ta5 LR BV SV

p1 576–750 290–390 630–880 320–420 190–320 160–260 70–104 1.79–2.44 1.69–2 1.26–1.47 p 2 460–630 400–490 312–332 100–150 50–110 42–90 45–70 0.54–0.70 3.3–4.68 3.57–4.32 p 3 700–760 460–600 384–412 216–220 204–170 85–130 63–85 0.50–0.76 2.48–2.8 3.31–5.13 fe ti ta1 ta2 ta3 ta4 ta5 LR BV SV

p 1 340–680 304–692 392–860 240–436 232–364 224–236 80–118 1.24–1.28 1.63–1.77 1.2–2.51 p 2 704–716 536–684 312–332 160–168 120–128 88 72–76 0.48–0.58 3.52–3.76 3.97–4.21 p 3 768–772 600–640 384–412 232–254 192–216 138–208 92–96 0.64–0.66 2.41–2.61 3.42–3.56 fe ti ta1 ta2 ta3 ta4 ta5 LR BV SV

p 1 375–775 170–350 1035 450 340 250 120 2.96 0.99 1.09

p 2 560–765 525–615 27–35 135–235 100–215 60–140 45–80 0.51–0.57 2.58–3.98 3.94–4.02 p 3 705–750 555–590 285–350 145–240 105–210 60–145 50–75 0.51–0.59 2.52–4.29 3.82–4.42 Wing. Length/width 2.86. VR 1.54–1.57 (1.56). Wing setae: brachiolum with 1 seta; Sc bare; R with 18; R1 with 22; R4+5 with 53; M bare; M1+2 with 42; M3+4 with 28; Cu with 28; Cu1 with 35; PCu with 56; An with 26 setae (n = 1).

Legs. Fore tibia with spur 24 µm long; 2 spurs of mid tibial combs unequal in size: 32 and 24 long; 2 spurs of hind tibial combs subequal in size: c. 20 long. Lengths and ratios of leg segments in Table 2.

Genitalia ( Figs 7–10 ). Tergite IX with 16 setae. Cercus 62 long. Seminal capsule 50–66 (58) long. Notum 152 (152) long.

Pupa (n = 9 except when otherwise stated)

Color brown yellowish. Total length 2320–2728 (2515).

Cephalothorax. Length 712–760 (734). Frontal apotome with frontal setae 22–32 (27) long (n = 2) ( Fig 11 ). Antepronotals taeniate 88 long (n = 1). Precorneals elongate and taeniate, anterior 164 long; median 168 long; posterior 104 long (n = 1).

Two pairs of narrowly taeniate dorsocentrals, Dc1 and Dc2 30 long; Dc3 28 long; Dc4 24 long (n = 1) ( Fig 12 ).

Thoracic horn 344–476 (395) µm long, with bare basal half, with small spinules on apical half ( Fig. 13 ).

Wing sheath with nose 14–16 (15) long (n = 4), as in Fig. 14 .

Abdomen ( Fig. 15 ). Length 1768–2752 (2202). Tergite I bare. Tergites II–VI each with paired patches of spines. Tergite II with posterior transverse row of hooks medially, about 40–70 (53) long (n = 5), weak shagreen present medially. Weak shagreen present anterolaterally on tergites II, III, VIII and IX and caudolaterally on tergites IV, V and VI. Lateral setae: segment II with 3 narrow taeniate setae, III with 1 narrow taeniate seta and 1 broad taeniate seta; IV–VIII with 4 taeniate setae 85–133 (115).Dorsal setae all simple ( Fig. 16 ). Ventral setae all bifid: II with 4, III–VII with 12 and VIII only 4 setae ( Fig. 17 ).

Segment VIII with darkened margins and two caudolateral spurs, smallest spur 16–20 (18) long; largest spur 28–36 (31) long (n = 3). Anal lobe fringe with 20–25 taeniate setae.

Larva (n = 8 except when otherwise stated)

Fourth instar larva. Color yellowish brown. Total length 2664–2792 (2715). Head capsule 276–308 (291) long, 200–212 (206) wide.

Head. Antenna with 5 segments placed on tall pedestal, as in Fig. 18 . Basal antennal segment 84–90 (87) long, 15 (15) wide, distance from base to ring organ 5–8 (7) and to basal mark of seta 48–53 (50); segment II 24–26 (25) long; segment III 6–8 (7) long; segment IV 3–5 (4) long; and segment V 2–4 (3) long. AR 2.05– 2.57 (2.31). Blade 20 (n = 1) long, accessory blade 16 long (n = 1), both truncate. Peg sensillum of second segment 4 long, and two subequal Lauterborn organs 4 long, pedicel 8 long (n = 1).

Labrum with fine and simple clypeal seta SIII.

Mandible ( Fig 19 ) 96–100 (98) long, seta subdentalis 46–48 (47) long (n = 2). Premandible and frontoclypeal apotome as in Figs 20 and 21 respectively. Mentum 67–70 (68) wide, 36–42 (39) high (n = 4). Mentum with 11 teeth, with median tooth with notches which may be more or less worn down ( Fig. 22 ). Ventromental plate 68 wide, 20 long, width/length 3.4 (n = 4), number of ventromental plate striations about 88.

Thoracic segments. With simple setae ( Fig. 23 ), anterior parapods with single claws.

Abdominal segments. With a pair of bifid multibranched setae ( Fig. 24 ). Procercus 8–12 (10), anal setae148–164 (159). Anal tubuli 40–60 (48).

Diagnosis and discussion. Male adults of Rheotanytarsus lamellatus can be separated from all other Neotropical species by: 1) short and strongly curved median volsella, 2) median volsella not extending beyond apex of superior volsella [except R. exiguus (Johannsen) and R. kusii Kyerematen & Andersen ], 3) with lamelliform setae fused into a plate [except R. meridionalis (Johannsen) ] and 4) 4–5 setae arranged in a line between anal tergite bands and anal point. Differing from R. exiguus on the presence of spurs on mid and hind tibiae, from R. kusii in having an oval superior volsella and from R. meridionalis in having a parallelsided anal point and gonostyli which are gradually tapered.

R. lamellatus specimens from Argentina are in general smaller than those reported by Reiss for Chilean specimens.

The pupa of R. lamellatus and R. exiguus share tergites II–VI with paired anterior patches of spinules, differing on that R. exiguus has a weak caudolaterally shagreen only on tergites IV and V and R. lamellatus posses anterolaterally shagreen on tergites II, III, VIII and IX and caudolaterally on tergites IV, V and VI.

Wiedenbrug & Ospina-Torres (2005) in their key to pupae of Tanytarsini from Neotropical region illustrated four morphotypes of Rheotanytarsus from Brazil, differing all of them from the species we described in this paper. Roback & Coffman (1983) described a pupa as Rheotanytarsus spp from Peru and Bolivia which may be conspecific to R. lamellatus , in having tergites II–VI with paired anterior patches of spinules, similar shagreen distribution and bifid ventral setae.

At present, the unique Rheotanytarsus pupa from Argentina is R. globosus Reiss (1972) and can be distinguished from R. lamellatus by having the former anterior paired point-patches on TII–V and segment VIII with 5 taeniate lateral setae.

Only two species are known from larvae in the Neotropical region. The larvae of Rheotanytarsus lamellatus differ from those of R. exiguus in being smaller; having bifid multibranched setae on abdominal segments, shorter antennae, lower AR, longer distance from base to ring organ as well as from base to basal mark of seta, shorter and more truncate antennal blades, higher ventromental width/length ratio, having a procercus that is shorter than 1/3 length of the anal setae. Cranston (1997) reported all Rheotanytarsus larvae from Australia present bifid multibranched setae on abdominal segments, similar to those of R. lamellatus .

Ecology and distribution. We collected our specimens from mountain streams in subtropical cloud forests. During low water periods, R. lamellatus larval density reached 16755 ind/m2, while this was reduced to 85 ind/m2 during high water periods. The difference in larval density denotes an important seasonal variation in this population of Rheotanytarsus lamellatus .

Figures

FIGURES 1 – 10. Adults of Rheotanytarsus lamellatus Reiss. Male: 1 — antenna, 2 — wing, 3 — hypopygium in dorsal view, 4 — median volsella, 5 — internal view of segment IX (sternapodeme and median tergite bands). Female: 6 — antenna, 7 — genitalia (ventral view), 8 — coxosternapodeme, 9 — ventrolateral lobe, 10 — dorsomesal lobe. Scale bar = 0.5 mm.

FIGURES 11 – 24. Immatures of Rheotanytarsus lamellatus Reiss. Pupa: 11 — frontal apotome, 12 — thorax, 13 — thoracic horn, 14 — wing nose, 15 — abdomen dorsal (spurs of VIII segment in detail), 16 — tergite III, 17 — sternite III (ventral lateral seta in detail). Larva: 18 — antenna, 19 — mandible, 20 — premandible, 21 — frontoclypeal apotome, 22 — mentum, 23 — simple seta, 24 — seta of abdominal segment.