Stempellinella leptocelloides (Webb)

Ekrem, Torbjørn, 2007, A taxonomic revision of the genus Stempellinella (Diptera: Chironomidae), Journal of Natural History 41 (21 - 24), pp. 1367-1465 : 1426-1432

Stempellinella leptocelloides (Webb)

Stempellina leptocelloides Webb 1969, p 94 . Holotype: „ (INHS no. 10.606) Canada, Ontario, Haliburton County, Algonquin Park, Costello Lake , 1 August 1965, D. W. Webb. Allotype: ♀. Paratypes: 35 „„, 108♀♀ as holotype [all examined].

Stempellinella leptocelloides (Webb) ( Poole and Gentili 1997). Giłka (2005) taxonomic placement.

Stempellinella cf. leptocelloides . Epler (2001) identification key to larva.

Additional material examined

Canada: 1 P(♀), 1 Pex, 1 „ ( ZMBN) British Columbia, Marion Lake , 11 June 1963, 5 July 1964, A. L. Hamilton; 2 „„ ( CNC) as previous except 30 June 1965, 18 July 1965; 1 P „ ( ZMBN) Manitoba, Southern Indian Lake, Long Bay, 13–15 June 1977, M. Collins; 1 „ ( ZMBN) Ontario, Kenora , Experimental Lake Area , 31 September 1975; 2 „„ ( JES) Quebeck , Terrobonne Co., St. Hippolyte , Lac Croche, 29 May 1972, P. P. Harper . USA: FL: 1 „ ( JHE) Camp Beach, 27 June 1997. NC: 1 „ ( JHE) Swain Co., confluence of Ocanluftee River and Ravens Fork, 3 October 2001, D. R. Jones and R. C. Harrington. MN: 1 Pex ( ZSM) St. Louis Co. , Lake Superior , French River outlet, 10 mi NE Duluth, 29 May 1999, R. E. Jacobsen; 5 Pex ( UMSP) Anoka Co. , Cedar Crk., upstream CR24, 45.4031 ° N, 93.2094 ° W, 19 May 2004, R. W. Brouchard Jr. OH: 1 LP in case, one larval case (VM) Wayne Co. , Apple Cr., RM 6.6 , ust, Ely Rd, 10 September 2002, J. T. Freda and K. E. McKnight; 1 L (VM) Champaign Co. , Little Darby Ck., RM41.2 Allison Rd. , 15 September 1997, L. E. McKnight; 1 P(„), 1 P, 1 LP („), 4 L ( MJB) Clark Co. , Medway Ck. at Spangler Rd. , 20 September 1991, M. J. Bolton. SC: „ ( JES) Aiken Co., Savannah River Plant, Tinker Ck., Malaise trap, 28–29 May 1980, P. L. Hudson; 1 „ as previous except Upper Three Runs Ck. , 12–13 May 1980 .

Diagnostic characters

Stempellinella leptocelloides can be separated from other Stempellinella species by the following combination of characters: adult male with AR 0.8–1.0; anal point widely triangular with numerous strong orally directed spinulae between well-developed anal crests; small median tergite setae at anal point base; lateral anal tergite setae present; anal tergite band weakly Tshaped; setiger of superior volsella oval with medially pointed apex; median volsella thin, 30 Mm long, stem simple, bare, lamellae simple. Adult female with AR 0.29; none to two setae on well-developed vaginal floor; spermathecal ducts longer than notum and rami combined; rami slightly shorter than notum; diameter of seminal capsules shorter than notum. Pupa with long, almost tubular cephalic tubercles and moderately wrinkled frontal apotome; thorax completely brown pigmented and extensively granulated, median antepronotal on well-developed tubercle; one lateral seta on abdominal segment III and IV taeniate; point patches on tergites IV – V usually separated both longitudinally and horizontally, giving the impression of four point patches; anterolateral patches of shagreen on tergites VII –IX. Larva with 18–25 Mm long, triangular spur on antennal pedestal, AR 0.7–0.9, antennal segment 2 long with proximal Lauterborn organ pedicel at one-sixth length; premandible with three teeth; S3 long, simple.

Redescription

Adult male (n 5 5, unless otherwise stated). Total length 1.5–1.8, 1.6 mm; wing length 0.91– 1.13, 1.02 (n 58) mm.

Colour: body and legs pale yellow; thorax with brown short scutal stripes, brown postnotum, preepisternum, and median anepisternum; eyes brown, darker ventrally.

Head ( Figure 21A, B ): eyes without dorsomedian elongation; frontal tubercle well developed, conical, 12–20, 16 Mm long; antenna ( Figure 21B ) with 13 flagellomeres of which only 10 are easily discernible; AR (on 10 flagellomeres) 0.85–1.01, 0.94; lengths of palpomeres (in Mm): 20–25, 25; 25; 55–65, 61; 65–80, 74; 90–110, 100. Clypeus about 50 Mm long with 6–12, 8 setae; tentorium ca 85 Mm long, 10 Mm wide; one or two inner verticals, two outer verticals, two postorbitals.

Thorax: scutal tubercle absent; acrostichals 10–12, 11; dorsocentrals 5–8, 6; humerals 0; prealars 1; scutellars 4–6; halterals 5.

Wing ( Figure 21C ): cuneiform, 3.0–3.3, 3.2 times longer than broad; VR 1.49–1.57, 1.53; costa proximal to M 3+4 (often more so than wing in Figure 21C ); wing setation as in Figure 21C .

Legs ( Figure 21D ): fore tibia with 20 Mm long spur; mid and hind tibiae with wellseparated, 10 Mm long tibial combs, both combs on each tibia with 15–20, 17 Mm long spur; tarsi without sensilla chaetica; pulvilli minute, reaching base of claws. Lengths and ratios of leg segments in Table III.

Hypopygium ( Figure 21E–G ): anal tergite 87–93, 89 Mm long with weakly T-shaped anal tergite band, four short median tergite setae at anal point base; lateral anal tergite seta present; anal point ( Figure 21F ) 40–47, 43 Mm long, broadly triangular, basally 15– 20, 16 Mm broad, with well-developed crests which end close to apex; 15–20, 17 strong, orally directed spinulae between anal crests; small microtrichia-free areas on each side of anal point base. Gonocoxite 80–85, 83 Mm long; gonostylus 50–58, 52 Mm long; HR 1.47–1.70, 1.60. Superior volsella ( Figure 21G ) comparatively small, setiger oval with medially directed apex, four dorsal and two median setae, superior volsella otherwise bare; digitus absent; median volsella thin, 27–30, 29 Mm long, posteriorly curved, stem simple with up to 25 Mm long, simple lamellae, without microtrichia; inferior volsella 63– 67, 66 Mm long, slightly club-shaped, with six distal setae, dorsal surface without microtrichia.

Adult female (n 5 5, unless otherwise stated). Total length 1.4–1.5 (n 53) mm; wing length 0.84–0.95, 0.90.

Colour: as male.

Head: as male, except cephalic tubercles 5–12, 10 Mm long; antenna ( Figure 21H ) with five flagellomeres, ultimate flagellomere 40–60, 50 Mm long, AR 0.27–0.30, 0.29; length of palpomeres (in Mm): 20–25, 22; 20–25, 24; 40–50, 44; 50–65, 60; 75–100, 92. Clypeus with 7–11, 9 setae.

Thorax: acrostichals 8–11, 9; dorsocentrals 5–6; humerals 0–2, 1; prealars 1; scutellars 4–6, 4; halterals 5.

Wing: as male, VR 1.48–1.51, 1.50.

Legs: as male.

Genitalia ( Figure 21I ): tergite IX slightly triangular, about 45 Mm long; sternite VIII with 15–20, 17 setae, of which 0–2, 0 are placed on vaginal floor; vaginal floor large, covering up to one-half of vaginal opening ventrally; gonapophysis VIII single lobe with long posteromedially directed microtrichia; gonocoxite IX with one or two setae; gonocoxapodeme strongly curved posteriorly; coxosternapodeme well developed with obvious anterior and posterior lobes. Notum including rami 110–120, 117 Mm long, notum alone ca 70 Mm long. Seminal capsules ovoid, diameter 37–50, 42 Mm with 120– 175, 155 Mm long spermathecal ducts. Postgenital plate broadly triangular. Cercus 35–50, 40 Mm long.

Pupa (n 5 5, unless otherwise stated). Total length 2.0–2.3, 2.2 mm; abdomen 1.6–1.7 mm long. Colour of pupal exuviae: thorax completely brown, abdomen clear with darker lateral margins on all segments, particularly segment VII –IX, tergites VII and VIII with dark pigmentation posteriorly.

Cephalothorax ( Figure 22A, B ): cephalic tubercle well developed, tubular, 40–50, 48 Mm long; frontal setae taeniate, 150–200 (n 52) Mm long; pedicel sheath tubercle weakly developed mound. Thoracic horn 330–400, 356Mm long with some 5–15, 8 Mm long chaetae distributed on distal three-quarters; precorneals taeniate, arranged in slight triangular pattern, the two anteriormost setae situated closer to each other than to the third, anterior and posterior precorneals ca 250 Mm long, median precorneal ca 225 Mm long; one taeniate median antepronotal ca 300 Mm long on well-developed tubercle, two lateral antepronotals (one sensillum basiconicum); two pairs of fine dorsocentrals, setae of anterior pair 30–50, 40 Mm long, slightly longer than setae of posterior pair, 25–35, 30 Mm long. Extensive fields of granulation and fine sculpturing present on thorax, a few stronger granules present along median suture line. Prealar tubercle weakly developed, wide; nose of wing sheath strong.

Abdomen ( Figure 22C ): TII with small, oval point patches starting posteriorly to seta D5; hook row 75–105, 91 Mm wide with 31–46, 36 hooks. TIII with more or less rectangular point patches; TIV with p -shaped point patch that often is divided in longitudinal and transverse sections, giving the appearance of four point patches; TV – VI with four point patches; TVII –IX (sometimes also TVI) 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, 2–3 V, 2 L, 1 taeniate L setae; segment IV with 3 D, 3 V, 2 L, 1 taeniate L setae; segment V with 2–3 D, 3 V, 3 taeniate L setae; segment VI – VII with 2–3 D, 3–4 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, 17–23, 20 taeniate setae in anal fringe. One pair of O-setae present anteriorly on tergites II – VII. Pleura IV with shagreen. Posterolateral spur on segment VIII well developed.

Larva (n 5 5, unless otherwise stated). Total length ca 2.6 mm, larval case ca 2.7 mm. Head capsule yellow, brown postoccipital rim and teeth on mandible and mentum. Live individuals not examined.

Head ( Figure 22D–I ): AR 0.74–0.91, 0.85; antennal pedestal 65–80, 71 Mm long with triangular, blunt, 18–25, 22 Mm long spur; antenna ( Figure 22D ) with all segments well sclerotized, segment lengths (in Mm): 43–60, 54; 31–47, 41; 9–10, 10; 7–9, 8; 4–6, 5; segment 3 inserted subapically on segment 2; AAR 1.24–1.55, 1.34. Antennal seta placed at base just above ring organ at base of antennal segment 1; antennal blade 60–88, 78 Mm long, pale, reaching well beyond tip of antenna; peg of antennal segment 2 placed at approximately four-fifths length of segment. Lauterborn organs large, bulbous, 13–18, 16 Mm long; proximal organ placed at one-sixth length of segment 2 on 5–8 Mm long pedicel, apical organ on 9–11 Mm long pedicel; SII and some chaetae pectinate, some chaetae and all chaetulae simple; S3 long and simple ( Figure 22E ); pecten epipharyngis consist of three well-developed, thin chaetae; labral lamella with ca 21 teeth. Mentum ( Figure 22F ) with 13 teeth, median tooth without lateral notches, first lateral teeth partly fused with median tooth, all teeth equally dark; ventromental plates medially reaching third lateral tooth of mentum, MVR ca 1.1; premandible ( Figure 22G ) with three teeth, welldeveloped brush; mandible ( Figure 22H ) with pecten mandibularis slightly convex, seta subdentalis 35–40, 38 Mm long, reaching beyond apex of mandible, mola without spines; postoccipital plate ( Figure 22I ) developed, not split.

Body: anterior parapods with long, simple spines; hind parapods with 14–16 simple hooks; L2 apparently simple; anal segment with anal tubules 50 Mm long; supraanal seta strong, 225 Mm long; procercus 25 Mm long with two short (ca 130 Mm long) and four long

(ca 550 Mm long) anal setae, the short setae situated individually, and not on the common base of the long setae.

Remarks

The holotype, allotype, and seven paratypes (3 „„, 4♀♀) have been mounted on microscope slides. Unfortunately, the type material was partly destroyed in the mail upon return to INHS. The holotype, one female paratype, and one male paratype were missing from the damaged package when it arrived in Illinois (C. Favret, personal communication). However, since there is no doubt of the species identity and all paratypes are conspecific, a neotype is not designated at this point .

Stempellinella leptocelloides has a characteristic anal point, and adult males can easily be distinguished from all other Stempellinella by this feature. Female adults, pupae and larvae are most similar to species in the edwardsi species group, but can be separated from most of these by the diagnostic characters given above. The larvae of Stempellinella edwardsi , in particular early instars, can be difficult or impossible to separate from those of S. leptocelloides and the characters used in the key below overlapped in material of S. edwardsi and S. leptocelloides from Canada and Norway examined by G. A. Halvorsen (personal communication).

Stempellinella leptocelloides has been recorded from many streams, small rivers and lakes throughout North America (see above), and is probably widely spread in the Nearctic Region. The larvae build straight, transportable cases of fine, pale silt specked with a few dark silt particles.

Figures

Figure 21. Stempellinella leptocelloides (Webb), imagines. (A–G) Male: (A) head; (B) antenna; (C) wing; (D) fore, mid, and hind tibiae; (E) hypopygium; (F) variation in anal point; (G) superior and median volsellae. (H, I) Female: (H) antenna; (I) genitalia.

Figure 22. Stempellinella leptocelloides (Webb), 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.