Stempellinella truncata (Freeman) Ekrem, 2007

Ekrem, Torbjørn, 2007, A taxonomic revision of the genus Stempellinella (Diptera: Chironomidae), Journal of Natural History 41 (21 - 24), pp. 1367-1465 : 1447-1452

Stempellinella truncata (Freeman) comb. n.

Stempellina truncata Freeman 1958, p 354 . Holotype: „ (BMNH) South Africa, Western Cape Province, Berg River, Driefontein, December 1954, K. M. F. Scott. Paratypes: 1 „, 1♀ (BMNH) as holotype; 1 „, 2♀♀ (BMNH) South Africa, Kwazulu Natal, Tugela River, Drakensburg , 5000 ft, 14–30 September 1953, A. D. Harrison [all examined].

Additional material examined

South Africa: 1 „ (VM), Western Cape Province, Cederberg, Sandrif, Driehoek River, Maalgat, 32 ° 25.5269S, 19 ° 07.8949E, 820 m a.s.l., 28 December 2004, T. Ekrem and E. Stur; 1 Pex ( PSC) as previous except 12–14 January 2004, P. S. Cranston; 3 L, 1 Lex, 2 Pex, 1 LP („) (VM), Western Cape Province, Cederberg, Grootkloof, Rondegatsrivier at Jamaka Organic Farm, 32 ° 20.5799S, 19 ° 01.4909E, 30 December 2004, T. Ekrem and E. Stur; 1 P(♀) ( PSC) as previous except 8–9 January 2005, P. S. Cranston; 2 Pex ( PSC), Western Cape Province, Jonkerhoek nr. Stellenbosch, 29 January 1998, P. S. Cranston; 1 LP, 1 Lex, 1 Pex ( AMGS), Western Cape Province, Franschoek, tributary to Berg River, 33 ° 58.0389S, 19 ° 04.8629E, 299 m a.s.l., 5 January 2005, T. Ekrem and E. Stur; 1♀, 1 „ ( AMGS: GEN 639 C, GEN 649 B), E Transvaal, Lone Creak near Sabie, reared in lab., 8 April 1961, 8 May 1961; 1 L ( AMGS) Kwazulu Natal, Tugela River, Pumphouse stables nr. Rugged Glen, 28 ° 419020S, 29 ° 009340E, stones in current, 4 October 1999; 1 L as previous except Royal Natal National Park , Mahoi River at visitors centre, 28 ° 419180S, 28 ° 569380E, stones in large pool, 3 October 1999; 4 L ( AMGS), Eastern Cape Province, Antelope Park Spruit, 30 ° 499020S, 28 ° 129300E, 4 October 1990, F. C. de Moor and H. M. Barber .

Diagnostic characters

Stempellinella truncata can be separated from other Stempellinella species by the following combination of characters: adult male with wing length ca 0.9 mm; AR about 0.6–0.9; anal point long, narrow, with 3–10 small spinulae between well-developed anal crests; strong median and lateral setae on anal tergite; superior volsella medially curved, basomedian seta on obvious tubercle; median volsella barely reaching apex of superior volsella, with microtrichose, palmate stem. Adult female with AR 0.29–0.30; few or no setae on vaginal floor; vaginal floor small, covering about one-quarter of vaginal opening ventrally; seminal capsules small, diameter less than length of notum; spermathecal ducts longer than notum and rami combined, but shorter than 200 Mm; notum longer than rami; coxosternapodeme with obvious anterolateral lobe. Pupa with well-developed, narrow, conical cephalic tubercles; thorax with anterodorsal sculpturing; anterior and posterior dorsocentrals fine, of equal length; thoracic horn long, thin with small, scattered chaetae on distal half; tergites II – VI with large point patches; pleurae IV – VII with shagreen. Larva with large (ca 40 Mm long), digitiform spur on antennal pedestal; AR ca 0.9; proximal Lauterborn organ placed on 5 Mm long pedicel, distal organ on 15–20 Mm long pedicel; antennal blade just reaching apex of distal Lauterborn organ; S3 split in three branches; premandible with three teeth.

Redescription

Adult male (n 5 5, unless otherwise stated). Total length 1.3–1.5, 1.4 (n 54) mm; wing length 0.81–0.99, 0.93 mm.

Colour: cleared specimens pale brown with somewhat darker scutal stripes, postnotum and antennal pedicels, eyes red with darker ventral margin.

Head ( Figure 29A–C ): eyes without dorsomedian elongation; frontal tubercle large, tubular, 12–20, 15 Mm long; antenna with 12 or 13 flagellomeres of which only 10 are easily discernible (see variation in Figure 29B, C ); AR (on 10 flagellomeres) 0.51–0.91, 0.64 (n 54); lengths of palpomeres (in Mm): 15–25, 20; 15–25, 20; 42–65, 55; 54–76, 70; 81– 119, 103. Clypeus about 40 Mm long with 9–12 setae; tentorium ca 90 Mm long, 16 Mm wide; two inner verticals, two or three outer verticals, two to four postorbitals.

Thorax: scutal tubercle absent; acrostichals 8–13, 11; dorsocentrals 5–8, 7; humerals 2; prealars 1; scutellars 6–8; halterals 5.

Wing ( Figure 29D, E ): cuneiform, 2.8–3.4, 3.1 times longer than broad; VR 1.62–1.64, 1.63; wing setation as in Figure 29D, E .

Legs ( Figure 29F ): fore tibia with 5–20, 13 Mm long spur; mid and hind tibiae with wellseparated, 9–15, 11 Mm long tibial combs, one comb on each tibia with 22–30, 28 Mm long spur; tarsi without sensilla chaetica; pulvilli absent. Lengths and ratios of leg segments in Table III.

Hypopygium ( Figure 29G, H ): anal tergite 72–94, 83 Mm long with transverse anal tergite band, four to seven, five strong median setae far from anal point base, one lateral seta, 16–25, 19 apical setae; anal point 33–45, 37 Mm long, basally 5–10, 7Mm broad with well-developed crests, distally thin and pointed; 3–10, 7 small spinulae between anal crests; microtrichia present around base of anal point. Gonocoxite 60–76, 68 Mm long; gonostylus 36–48, 42 Mm long; HR 1.37–1.90, 1.63. Superior volsella medially curved with three dorsal and three median setae on setiger, basomedian seta on obvious tubercle, superior volsella otherwise bare; digitus absent; median volsella ca 30 Mm long, posteriorly directed, palmate stem with long microtrichia and 5–12, 7 Mm long simple lamellae; inferior volsella ca 50 Mm long, slightly club-shaped, with several distal setae, dorsal surface without microtrichia.

Adult female (n 5 4, unless otherwise stated). Total length 1.0–1.2, 1.1; wing length 0.82– 1.03, 0.94.

Colour: as male except antennal pedicels pale.

Head: as male, except cephalic tubercles 5–13, 8 Mm long; antenna ( Figure 29I ) with five flagellomeres, ultimate flagellomere 50 Mm long, AR 0.29–0.32, 0.31; lengths of palpomeres (in Mm, n 53): 25; 20; 45–50, 48; 65–70, 68; 115–120 (n 52). Clypeus with 7–10, 9 setae.

Thorax: scutal tubercle weak hump; acrostichals 12–15, 14; dorsocentrals 5–7, 6; humerals 2–3; prealars 1; scutellars 5–6; halterals 5.

Wing: as male, except 2.7–3.1, 2.9 times longer than wide; VR 1.51–1.73, 1.61.

Legs: as male except up to two sensilla chaetica on mid tarsus 1.

Genitalia ( Figure 29J ): tergite IX slightly triangular, about 38 Mm long; sternite VIII with 18–28, 22 setae, of which none to two are placed on vaginal floor; gonapophysis VIII single lobe with long medially directed microtrichia; gonocoxapodeme slightly curved; coxosternapodeme well developed with obvious anterior and posterior lobes. Notum including rami 90–111, 100 Mm long, notum alone ca 60–82, 72 Mm long. Seminal capsules ovoid, diameter 35–52, 43 Mm with 100–195, 146 Mm long spermathecal ducts. Postgenital plate subtriangular. Cercus 30–40, 36 Mm long.

Pupa (n 5 5, unless otherwise stated). Total length 1.6–2.2, 1.9 mm; abdomen 1.2–1.6, 1.4 mm long. Colour of pupal exuviae pale brown with darker lateral margins on abdomen, in particular on segment VIII.

Cephalothorax ( Figure 30A, B ): cephalic tubercle well developed, narrow, conical, 27– 33, 30 Mm long; frontal setae taeniate, 120–192, 150 Mm long; pedicel sheath tubercle absent. Thoracic horn 270–360, 303 Mm long with some minute chaetae scattered on distal half; precorneals taeniate, arranged in slight triangular pattern, the two anteriormost setae situated closer to each other than to the third, anterior precorneal ca 210 Mm, longer than other two (130–150 Mm long); one taeniate median antepronotal ca 270 Mm long, two lateral antepronotals (one sensillum basiconicum); two pairs of fine dorsocentrals, setae of each pair equally strong. Fine sculpturing present on thorax, a few stronger granules present along median suture line. Prealar tubercle well developed, wide; nose of wing sheath strong.

Abdomen ( Figure 30C ): TII with comparatively large, oval to subtriangular point patches; hook row 60–90, 79 Mm wide with 28–39, 35 hooks. TIII – VI with p -shaped point patches, patches on TIII somewhat smaller; TVII –IX with small anterior patches of shagreen. Segment II with well-developed pedes spurii B; segment IV with pedes spurii A. Segment II with 2 D, 2 V, 3 L setae; segment III with 3 D, 3 V, 2 L, 1 taeniate L setae; segment IV with 3 D, 3 V, 2 L, 1 taeniate L setae; segment V with 3 D, 3 V, 3 taeniate L setae; segment VI – VII with 3 D, 3 V, 4 taeniate L setae, segment VIII with 1 D, 1 semi-taeniate V, 3 taeniate L setae; segment IX with 1 D seta on anal lobe, 13–16, 15 taeniate setae in anal fringe. One pair of O-setae present anteriorly on tergites II – VII. Pleurae IV – VII with anterior shagreen. Posterolateral spur on segment VIII well developed.

Larva (n 5 4, unless otherwise stated). Total length ca 1.8 mm, larval case ca 2 mm. Head capsule brown, dark brown postoccipital rim and teeth on mandible and mentum. Live individuals with light yellow body.

Head ( Figure 30D–I ): AR 0.82–0.95, 0.89; antennal pedestal 54–60, 57 Mm long with strong, 36–42, 40 Mm digitiform spur; antenna ( Figure 30D ) with all segments well sclerotized, segment lengths (in Mm): 51–63, 51; 33–36, 34; 12–18, 15; 8–11, 10; 4–6, 5; segment 3 inserted subapically on segment 2; AAR 0.90–1.11, 1.00. Antennal seta placed at base just above ring organ; antennal blade ca 70 Mm long, pale, reaching slightly beyond tip of antenna; peg of antennal segment 2 placed at two-thirds length of segment. Lauterborn organs large, bulbous, 21–24, 23 Mm long; proximal organ placed at one-third length of segment 2 on 5 Mm long pedicel, apical organ on 15–20 Mm long pedicel; SII and chaetae plumose; chaetulae simple; S3 long and split in three branches ( Figure 30E ); pecten epipharyngis consists of three well-developed chaetae; labral lamella with ca 20 teeth. Mentum ( Figure 30F ) with 13 teeth, median tooth without lateral notches, somewhat paler; ventromental plates medially reaching second lateral tooth of mentum, MVR ca 1.2; premandible ( Figure 30G ) with three teeth, well-developed brush; mandible ( Figure 30H ) with pecten mandibularis slightly convex, seta subdentalis 36 Mm long; postoccipital plate ( Figure 30I ) well developed.

Body: anterior parapods with long, simple spines; hind parapods with 12–16 simple hooks; L2 apparently simple; anal segment without anal tubules; supraanal seta strong, ca 200 Mm long; procercus with two short (ca 110 Mm long) and four long (ca 500 Mm long) anal setae, the short setae situated individually, and not on the common base of the long setae.

Remarks

The species fits the diagnostic characters for the genus Stempellinella , and is hereby transferred to this genus. The male specimens from Natal and eastern Transvaal differ from specimens from the Western Cape Province by having a broader wing, lower AR, narrower antennal plume and somewhat higher crests of the male anal point (on equal-sized specimens). These differences are here regarded as intraspecific, but future molecular data or immature stages from the northern populations (which were unavailable for this study) might recognize the two populations as separate species.

Stempllinella truncata is a common species in clear, fast-flowing streams and smaller rivers in mountainous areas of South Africa. The water is neutral or slightly alkaline (pH 7–8), and the stream beds typically consist of boulders, cobbles, and some bedrock. The larvae and pupae of S. truncata live in sand and silt in quiet backwater sections where they build their small cases of sand grains and organic particles.

Figures

Figure 29. Stempellinella truncata (Freeman), imagines. (A–H) Male: (A) head; (B) antennal flagellum; (C) variation in antennal flagellum; (D) wing; (E) variation in wing; (F) fore, mid, and hind tibiae; (G) hypopygium; (H) superior and median volsellae. (I, J) Female: (I) antenna; (J) genitalia.

Figure 30. Stempellinella truncata (Freeman), immatures. (A–C) Pupa: (A) frontal apotome; (B) thorax; (C) abdomen, dorsal view. (D–I) Larva: (D) antenna; (E) clypal seta S3; (F) mentum and ventromental plates; (G) premandible; (H) mandible; (I) postoccipital plate.