Stempellinella flavidula (Edwards)

Ekrem, Torbjørn, 2007, A taxonomic revision of the genus Stempellinella (Diptera: Chironomidae), Journal of Natural History 41 (21 - 24), pp. 1367-1465 : 1417-1423

Stempellinella flavidula (Edwards)

Tanytarsus (Stempellina) flavidulus Edwards 1929, p 420 . Lectotype „ ( BMNH 235921 , here designated) England, Bedfordshire , Barton Hills, 8 June 1929, F. W. Edwards. Paralectotypes: 1 „ ( BMNH 236468 ) as lectotype [examined]; 1 „ ( BMNH 236369 ) as lectotype except Barton, 8–9 July 1928 [examined]; 1 „, 1♀ (BMNH) [not examined].

Stempellina flavidula (Edwards) . Goetghebuer (1937 –54) key.

Additional material examined

Austria: 1 Pex ( SM), 1 LP „, 1 LP ♀ (To161, To162, VM) Salzkammergut, Schwarzensee, 716 m a.s.l., 8 August 1997, 15 August 2004, S. Michiels; 2 Pex (VM) as previous except Eibensee, Wildmoos, 14 August 1999; 2 Pex ( SM) Oberösterreich, Attersee, Alexenauer Bach, 3 August 1998, S. Michiels. England: 1 „, 1♀, 7 Pex, 1 L ( ZSM); 2 „„, 2♀♀, 3 Pex, 1 LP, 2 L ( PHL) Cranham Woods, chalk spring stream, 25 August 1986, P. H. Langton. Germany: 2 Pex (1 SM, 1 VM) Bavaria, Burghausen, Salzach, 8 September 1996, 12 April 1997, S. Michiels; 1 Pex ( SM) Bavaria, Heroldsberg, Simmelberger Grundlach, 4 September 2000, C. Orendt; 7 Pex, 1 „ ( ZSM) Bavaria, Murnauer Moos, Ramsach, drift, 19 September 1978, R. Kühbandner; 6 Pex, 3 „„ as previous except 20 August 1978, 21 June 1978, F. Reiss; 1 Pex ( ZSM) Bavaria, Osterseen, Stechsee, 16 May 1980, F. Reiss; 1 „ ( ZSM) Baden-Württemberg, Bodensee, Überlingen, 1 May 1964, F. Reiss; 1 „, 1 LP (♀) ( ZSM) Bavaria, Berchtesgaden National Park, Herrenroint spring # 312, 6 June 2001, 14 June 2001, E. Stur and S. Wiedenbrug; 2 Pex ( SM) Rheinland-Pfalz, Hunsrück, Ehrbach, 31 August 1996, S. Michiels; 1 LP „, 1 LP ♀, 2 L, 8 L cases (VM) Hessen, Marburg-Biedenkopf, Mardorf, Spring and Marbach, 10 May 2000, 1 June 2000, 5 June 2000, A. Sundermann; 1 LP, 1 „ (To193, To194, VM) as previous except 10 May 2000, 21 June 2000; 1 „ ( ZSM) Ost-Holstein, Redensburg-Eckernförde, Fuhlenau, 4 September 1981, K. Mikowski. Luxembourg: 1 „ (To110,VM) Gutland, SW Kopstal, Rheocrene spring E7, emergence trap, 1 June 1999, I. Schrankel; 5 „„ ( MGDL) as previous except 4 May 1999, 18 May 1999, 29 June 1999; 11 „„ ( MGDL) Gutland, SE Dellen, Waldrand, Rheohelocrene spring E5, emergence trap, 4 May 1999, 18 May 1999, 1 June 1999, 15 June 1999, I. Schrankel; 1 Pex as previous except 1 May 2002, P. Martin.

Diagnostic characters

Stempellinella flavidula can be separated from other species in Stempellinella by the following combination of characters. Adult male with medially pointed superior volsella apex; anal point long and slightly triangular with long crests which end far distal on the anal point, several short spinulae between crests; lamellae of median volsella reaching two-thirds length of inferior volsella; obvious microtrichose wart basally on inferior volsella. Adult female with large seminal capsules, diameter as large as or larger than length of notum excluding rami and considerably larger than length of cercus; spermathecal duct considerably longer than notum including rami; vaginal floor large, covering one-third to one-half of vaginal opening ventrally; gonocoxapodeme almost straight. Pupa with large, broad conical cephalic tubercles; strong chaetae dorsally on thoracic horn mid section; shagreen on pleurae III – VII; point patches on tergite VI transversely divided; anterolateral patches of shagreen on tergite VII. Larva with moderate (ca 18 Mm long), digitiform spur on antennal pedestal; antennal blade reaching apex of distal Lauterborn organ; AR ca 0.8–1.0; S3 split in three or four branches; distal Lauterborn organ pedicel about twice as long as proximal Lauterborn organ pedicel; premandible with two teeth.

Redescription

Adult male (n 5 5, unless otherwise stated). Total length 1.6–1.9, 1.75 mm; wing length 1.08– 1.30, 1.20 mm.

Colour: pale brown thorax with dark brown scutal stripes, postnotum, preepisternum, median anepisternum, and antennal pedicels; abdomen yellow-green; eyes uniformly dark brown.

Head ( Figure 17A, B ): eyes without dorsomedian elongation; frontal tubercle large, conical, 11–21, 16 Mm long; antenna ( Figure 17B ) with 13 flagellomeres of which only 10 are easily discernible; AR (on 10 flagellomeres) 0.82–1.05, 0.95 (n 56); lengths of palpomeres (in Mm): 22–32, 25; 24–34, 27; 66–79, 72; 75–97, 86; 114–138, 130. Clypeus about 65 Mm long with 8–11, 10 setae; tentorium ca 95 Mm long, 16 Mm wide; two or three inner verticals, one to three outer verticals, two or three postorbitals.

Thorax: scutal tubercle absent; acrostichals 10–16, 13; dorsocentrals 5–8, 7; humerals absent; prealars 1; scutellars 4–7, 5; halterals 5.

Wing ( Figure 17C ): cuneiform, 3.1 times longer than broad; VR 1.41–1.52, 1.44; wing setation as in Figure 17C .

Legs ( Figure 17D ): fore tibia with 12–18, 15 Mm long spur; mid and hind tibiae with well separated, 11 Mm long tibial combs, one mid tibial comb with 30–32 Mm long spur, one hind tibial comb with 28–32, 30 Mm long spur; mid tarsus 1 without sensilla chaetica; pulvilli absent. Lengths and ratios of leg segments in Table III.

Hypopygium ( Figure 17E, F ): anal tergite 92–104, 98 Mm long with transverse anal tergite band; three to seven, four strong median setae at some distance from anal point base, none or one lateral seta, 20–24, 21 apical setae; anal point 39–49, 43 Mm long, basally 10–12 Mm broad with long, well-developed crests which end close to anal point apex; 7–15, 9 small spinulae between anal crests; microtrichia-free area on either side of anal point base. Gonocoxite 85– 97, 92 Mm long; gonostylus 60–76, 65 Mm long; HR 1.28–1.50, 1.42. Superior volsella with strongly tapered, medially directed apex, with four to six, five dorsal and two median setae on setiger, superior volsella otherwise bare; digitus absent; median volsella 24–30, 27 Mm long, straight, posteromedially directed, stem simple with numerous simple 25 Mm long lamellae which at most reach two-thirds length of inferior volsella; inferior volsella 54–76, 61 Mm long, slightly club-shaped, with several distal setae, dorsal surface without microtrichia, obvious microtrichose wart basally on inferior volsella.

Adult female (n 5 5, unless otherwise stated). Total length 1.3–1.6, 1.4 (n 54) mm; wing length 0.96–1.16, 1.09 (n 54) Mm long.

Colour: pale green with light brown eyes and pedicels.

Head: as male, except cephalic tubercles ca 12 Mm long; antenna ( Figure 17G ) with five flagellomeres, ultimate flagellomere 52–75, 63 Mm long, AR 0.26–0.35, 0.29; lengths of palpomeres (in Mm): 21–27, 22; 21–27, 23; 60–72, 65; 69–75, 65; 97–123, 109 (n 54). Clypeus with 8–11, 10 (n 54) setae.

Thorax: acrostichals 14–17, 15; dorsocentrals 5–7, 6; humerals 1–2; prealars 1; scutellars 4–7, 6; halterals 5.

Wing: as male, except 2.8–3.0, 2.9 times longer than broad, VR 1.41–1.64, 1.51.

Legs: as male, except one or two sensilla chaetica distally on mid tarsomere 1.

Genitalia ( Figure 17H ): tergite IX slightly triangular, about 45 Mm long; sternite VIII with 24–30, 26 setae, of which one or two are placed on vaginal floor; vaginal floor large, covering one-half of vaginal opening ventrally; gonapophysis VIII single lobe with long posteromedially directed microtrichia; gonocoxapodeme only slightly curved; coxosternapodeme well developed with obvious anterior and posterior lobes. Notum including rami 123–141, 133 Mm long, notum alone ca 70 Mm long. Seminal capsules ovoid, large, diameter 63–72, 69 Mm with 186–255, 230 (n 54) Mm long spermathecal ducts. Postgenital plate triangular. Cercus 33–42, 38 Mm long.

Pupa (n 5 5, unless otherwise stated). Total length 1.9–2.2, 2.1 mm; abdomen 1.4–1.6, 1.5 mm long. Colour of pupal exuviae pale brown with darker lateral margins on abdominal segments VII – VIII.

Cephalothorax ( Figure 18A, B ): cephalic tubercle well developed, broad conical, 21–36, 28 Mm long; frontal setae taeniate, 111–195, 134 Mm long; pedicel sheath tubercle absent. Thoracic horn 255–315, 285 Mm long, 21–24, 22 Mm wide with well-developed 7–12, 9 Mm long, strong chaetae dorsally on mid section of horn; precorneals taeniate, ca 120–200 Mm long, arranged in row on obvious mound; median antepronotal taeniate, two lateral antepronotals: one taeniate, one sensillum basiconicum; two pairs of fine dorsocentrals, all about 30 Mm long. Area of fine sculpturing anteriorly on thorax, a few strong granules present along median suture line. Prealar tubercle well developed, wide; nose of wing sheath strong.

Abdomen ( Figure 18C ): TII with triangular or trapezoidal posteriomedian point patch posteriorly to seta D1; hook row 75–100, 92 Mm wide with 26–41, 35 hooks. TIII – V with p - shaped point patches; TVI with two pairs of point patches, anterior pair in middle of tergite; TVI –IX with anterolateral patches of shagreen. Segment II with pedes spurii B; segment IV with pedes spurii A. Segment II with 2 D, 2 V, 3 L setae; segment III with 3 D, 2 V, 2–3 L, 0–1 semi-taeniate L setae; segment IV with 3 D, 2 V, 2–3 L, 0–1 semi-taeniate L setae; segment V with 4 D, 3 V, 3 taeniate L setae; segment VI – VII with 3 D, 2 V, 4 taeniate L setae, segment VIII with 1 semi-taeniate D, 1 semi-taeniate V, 3 taeniate L setae; segment IX with 1 D seta on anal lobe, 14–20, 16 taeniate setae in anal fringe. One pair of O-setae present anteriorly on tergites II – VII and anterolaterally on sternites II – VIII. Pleurae III – VII with shagreen. Posterolateral spur on segment VIII well developed.

Larva (n 5 5, unless otherwise stated). Total length ca 2.5 mm, case ca 3 mm. Head capsule brown, somewhat darker postoccipital rim and teeth on mandible and mentum. Live individuals not examined.

Head ( Figure 18D–I ): AR 0.83–1.01, 0.90; antennal pedestal 51–75, 67 Mm long with developed, 15–21, 18 Mm digitiform spur; antenna ( Figure 18D ) with all segments well sclerotized, segment lengths (in Mm): 60–69, 64; 45–59, 48; 9; 9; 5; segment 3 inserted subapically on segment 2; AAR 0.81–1.19, 1.03. Antennal seta placed at base just above ring organ; antennal blade ca 90–99 Mm long, pale, reaching slightly beyond tip of distal Lauterborn organ; peg of antennal segment 2 placed subapically on segment. Lauterborn organs large, bulbous, 15 Mm long; proximal organ placed close to base of segment 2 on 9 Mm long pedicel, apical organ on 15–24, 20 Mm long pedicel; SII slightly plumose, chaetae pectinate, chaetulae simple; S3 split in three or four branches ( Figure 18E ); pecten epipharyngis consists of three well-developed chaetae, labral lamella with ca 30 teeth. Mentum ( Figure 18F ) with 13 teeth, median tooth with weak lateral notches, somewhat paler, all lateral teeth set in equal distance to each other; ventromental plates medially barely reaching second lateral tooth of mentum, MVR ca 1.1; premandible ( Figure 18G ) with two teeth, well-developed brush; mandible ( Figure 18H ) with pecten mandibularis slightly convex, seta subdentalis 42 Mm long; postoccipital plate ( Figure 18I ) narrow, split in middle.

Body: anterior parapods with long, simple spines; hind parapods with 14–16, 15 simple hooks; L2 simple; anal segment with four narrow anal tubules, 58 Mm long; supraanal seta strong, ca 230 Mm long; procercus ca 30 Mm long with two short (ca 130 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

A lectotype is here designated to promote future nomenclatural stability.

Stempellinella flavidula has been recorded from Austria, the British Isles, Corsica, Germany, Ireland, Luxembourg, Poland, Slovakia, and Switzerland ( Saether and Spies 2004; above), but previous records of the species might have been of S. ciliaris as this species is quite similar in the adult and immature stages. The larvae of S. flavidula build small, straight transportable cases of sand and detritus, and are typically found in calcareous springs, spring brooks, and small streams. The species has been found to be host to several water mite species in springs in Luxembourg ( Stur et al. 2005).

Figures

Figure 17. Stempellinella flavidula (Edwards), imagines. (A–F) Male: (A) head; (B) antennal flagellum; (C) wing; (D) fore, mid, and hind tibiae; (E) hypopygium; (F) superior, median, and inferior volsellae. (G, H) Female: (G) antenna; (H) genitalia.

Figure 18. Stempellinella flavidula (Edwards), 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.