Polypedilum (Pentapedilum) tritum (Walker)

Oyewo, Emmanuel Adeoye & Saether, Ole A., 2008, Revision of Polypedilum (Pentapedilum) Kieffer and Ainuyusurika Sasa et Shirasaki (Diptera: Chironomidae), Zootaxa 1953, pp. 1-145 : 110-114

Polypedilum (Pentapedilum) tritum (Walker)

( Fig. 37)

Chironomus tritus Walker, 1856: 162 , 342.

Tanytarsus longiseta Kieffer, 1913: 29 ; Goetghebuer (1921: 110).

Polypedilum (Pentapedilum) tritum (Walker) ; Edwards (1929: 376), Townes (1945: 62).

Pentapedilum fulvescens? Townes, 1937: 171 .

Polypedilum (Pentapedilum) albulum Townes, 1945: 63 .

Polypedilum (Pentapedilum) uncinatum auct ., not Goetghebuer (1921: 110).

Polypedilum (Pentapedilum) muscicola auct ., not Kieffer (1924: 36).

Material examined. ENGLAND: paratype female, F. Walker ( BMNH No. 235846) . BELGIUM: Destelbergen , 2 males, 31.viii.1921, 12.viii.1916, 1 female, 25.iv.1921, M. Goetghebuer ( IRSN No. 847/07) ; La Panne , 1 male, 12.ix.1931, M. Goetghebuer ( IRSN) ; Dickebusch , 1 male, 03.ix.1936, M. Goetghebuer ( IRSN) ; Heusden , 1 male, 30.xi.1930, M. Goetghebuer ( IRSN) . NORWAY: Aust-Agder, Birkenes, Store Hovvatn , 1 male, 15.vii.1989, Ø. A. Schnell ( ZMBN) . PORTUGAL: Lagoa de Barrinha, Praia de Mira , 1 male, 30.iv.1985, L. Why Honda Terra ( ZSM) . GERMANY: Ost-Holstein, Unterer Schierenseebach , 1 male, 10.v.1985, U. Holm

( ZSM No. 197). SPAIN: Province Huelva, Las Marismas, El Rosio, 1 male, 21.iv.1979, W. Schacht ( ZSM) . CANADA: Winnipeg, B.P.P. Delta Marsh, 1 male, 26.v.1980, D. Wrubleski ( ZSM No. CH5278) ; Ontario, Experimental Lakes Area , 1 male, 1984–1986, B. Bilyj . USA: Minnesota, Shoreview Pond, University of Minnesota, 4 males, 22.v.1969, D. E. Maschwitz ( UMSP); Ohio, Geauga, Fern lake Bog, 2 pupae & larvae, 12.vi.1992, 2.viii.1992, M. J. Bolton; Pennsylvania, Raccoon Creek , Sanner Rd. , 1 pupa, 2 larvae, 21.viii.1992, M. J. Bolton; Pennsylvania, Tinkers Creek , 2 larvae 20.viii.1993, M. J. Bolton ( ZMNB) .

Diagnostic characters. The species differs from other species with numerous macrotrichia on the wing, uniformly colored abdomen, and spur on the foretibia, except P. (Pe.) epleri . It differs from P. (Pe.) epleri by having a higher base of the superior volsella and slightly higher antennal ratio (about 1.6 as opposed to 0.9– 1.2). This species is similar to P. (Pe.) uncinatum , which, however, lacks a spur on the foretibial scale. The projection of the superior volsella is less curved in P. (Pe.) tritum than in P. (Pe.) uncinatum . The female genitalia is similar to those of P. (Pe.) uncinatum , but the females can be distinguished by the shape of the lobes of gonapophysis VIII, as the ventrolateral lobe is slender, brush-like and slightly curved, while that of P. (Pe.) uncinatum is broad. The pupa has tergite II without shagreen, strong bands of anterior spines on tergites II – VI; tergite VII with fine anterolateral spinules and tergite VIII bare; tergite II with 31–47 caudal hooklets; pedes spurii B and A well developed on segment II and IV respectively; conjunctives III / IV and IV / V each with bands of spinules; and anal lobe with 20–26 taeniae. The larva has a dorsal tooth on the mandible, third antennal segment is slightly longer than fourth, the antennal blade is shorter than the flagellum, the Lauterborn organs virtually absent, and the mentum has the median teeth slightly longer or subequal to the second lateral tooth, with first lateral tooth shorter than the third.

Male (n = 10–15, unless otherwise stated)

Total length not measurable. Wing length 1.71–2.19, 1.91 mm. Wing length / length of profemur 2.18– 2.75, 2.43. Thorax brown; abdomen pale brown to brown; femur, tibia and tarsi brown.

Head. AR 1.41–1.79, 1.55. Ultimate flagellomere 556–729, 640 µm long. Temporal setae 8–13 including 3–6, 4 inner verticals; 3–5, 4 outer verticals; and 1–3, 2 postorbitals. Clypeus with 14–27, 19 setae. Tentorium 114–140, 125 µm long, 6–13, 8 µm wide at posterior tentorial pit. Stipes 119–155, 133 µm long. Palpomere lengths (in µm): 29–45, 76; 35–52, 46; 118–164, 137; 114–145, 132; 148–238, 192. Fifth palpomere / third palpomere 1.12–1.59, 1.44 (7). Third palpomere with 2–3 sensilla clavata.

Thorax. Acrostichals 7–17, 13; dorsocentrals 12–26; 17, prealars 4–5, 5. Scutellum with 5–13, 10 setae.

Wing. Anal lobe moderately developed. VR 1.10–1.23, 1.15. Brachiolum with 1–4, 1 setae; R with 23–57, 38; R 1 with 13–48, 34; R 4+5 with 32–93, 77; Sc with 14–33, 21; RM with 1–3, 2; M with 1–15, 10; M 1+2 with 40–65, 52; M 3+4 with 33–52, 40; Cu with 27–42, 38; Cu 1 with 14–49, 19, PCu with 31–56, 44; An with 21–46, 31 setae. Cells r 4+5, m 1+2, m 3+4, apparently all with more than 100 macrotrichia; cell m basal of RM with 20–55, 30 macrotrichia. Squama with 6–9, 7 (8) setae.

Legs. Scale on foretibia ( Figs 37A–D) 26–51, 37 µm long; with 14–21, 18 µm long apical to subapical spur. Spurs on midtibia 36–65, 53 µm long; on hind tibia 48–71, 57 µm long. Comb on midtibia 13–31, 23 µm long; combs on hind tibia 16–27, 23 µm and 12–28, 20 µm long. Width at apex of foretibia 36–55, 46 µm; of midtibia 38–63, 50 µm; of hind tibia 40–68, 53 µm. Length and proportions of legs as in Table 46.

Hypopygium ( Fig. 37E). Tergite IX with 7–15, 8 median setae; laterosternite IX with 1–3, 2 setae. Anal point 27–70, 59 µm long; 4–19, 10 µm wide at base, gradually tapering to nearly parallel-sided towards 4–7, 6 µm wide apex. Transverse sternapodeme 27–71, 52 µm long; phallapodeme 52–119, 74 µm long. Gonocoxite 98–176, 153 µm long. Superior volsella ( Fig. 37 I–N) 42–69, 60 µm long; base with sparse microtrichia and 3–4 inner setae; projection with 1 lateral seta. Inferior volsella ( Fig. 37 H) 82–136, 113 µm long; parallelsided, with prominent apical seta. Gonostylus ( Fig. 37G, H) 95–171, 158 µm long. HR 0.89–1.23, 0.97.

Female (n = 2)

Total length not measurable. Wing length 2.12–2.20 mm. Wing length / length of profemur 2.57–2.94. Thorax and abdomen pale brown to brown; femur, tibia and tarsi brown.

Head. AR 0.37–0.39. Length of flagellomeres (in µm): 136–139, 87–96, 90–98, 48–60, 140–147. Temporal setae 11 including 4–5 inner verticals, 4 outer verticals, and 3–4 postorbitals. Clypeus with 25–26 setae. Tentorium 114–169 µm long; 9–11 µm wide at sieve pore. Palpomere length (in µm): 44, 52, 133, 143, fifth segment lost.

Thorax. Acrostichals 12–14, dorsocentrals 18–31, prealars 6. Scutellum with 9–12 setae.

Wing. Anal lobe moderately developed. VR 1.12. Brachiolum with 1–5 setae, R with 41, R 1 with 36–45, R 4+5 with 84, Sc with 23–37, RM with 4, M with 14–18, M 3+4 with 56–65, PCu with 74, M 1+2 with 72, Cu with 42–44, Cu 1 with 23–27 and An with 44 setae. Wing membrane densely covered with macrotrichia. Squama with 9–11 setae.

Legs. Scale on foretibia including apical spur 45–61 µm long. Spurs on midtibia 52–63 µm long, on hind tibia 52–79 µm long. Comb on midtibia 26–27 µm long, combs on hind tibia 28–31 µm and 19–26 µm long. Width at apex of foretibia 51–60 µm, of midtibia 54–62 µm, of hind tibia 62–63 µm. Length and proportions of legs as in Table 47.

Genitalia ( Fig. 37O). Gonocoxite IX with 6 setae, tergite IX with 23 setae. Segment X with 4–6 setae. Cercus 90–105 µm long, 5–9 µm wide at tip. Seminal capsule ovoid, 49–57 µm long, 24–40 µm wide; with sclerotized neck,18 µm long. Notum 139–188 µm long. Dorsomesal lobe ( Fig. 37Q) 71–85 µm long, 23–38 µm wide; ventrolateral lobe ( Fig. 37P) and apodeme lobe not discernable. Postgenital plate broadly triangular.

Pupa (n = 3, unless otherwise stated)

Exuviae with cephalothorax, margins of segments and caudolateral spur brown.

Cephalothorax. Cephalic tubercules absent. Frontal setae 30 (1) µm long. Prealar tubercle apparently absent. Wing sheath 1.08–1.28–2.12 (2) mm long.

Abdomen. Tergite I bare; tergites II – VI with strong, prominent anterior row of spines; tergites II – III with weak, sparse spinules in median shagreen, tergite II occasionally bare; tergites IV – VI with weak medial to posterior shagreen. Tergites VII and VIII without shagreen; tergite VII with paired anterolateral spots of spinules, tergite VIII bare. Conjunctive III / IV and IV / V each with 3–4 or multiserial bands of anterior pointed spinules. Tergite II with single row of about 31 (1) caudal hooks. Pedes spurii A present on segment IV. Pedes spurii B weakly developed on segment II. Caudolateral spur 49–85 µm long, with 1 strong apical tooth, 2–4 lateral teeth, and several accessory points; or bifid, with 3 inner and 1 lateral teeth plus several accessory points. Segments I– IV without L taeniae, segments V – VI with 3 taeniae; VII – VIII with 4 taeniae. Anal lobe fringe with 20–26 taeniae. Length of genital sac overreach 138–159 (2) µm.

Larva (n = 6, unless otherwise stated)

Postmentum 99–108, 109 (4) µm long. Head segments brown with postoccipital margin, teeth of mentum and mandible dark brown. Frontal apotome not discernible.

Head. AR 0.84–1.28, 1.03 (4), antenna 5-segmented, segment lengths (in µm) 39–58, 50 (5); 16–21, 18 (5); 15–18, 16 (5); 9–15, 13 (4); 5–7, 6 (4). Basal antennal segment 14–16, 14 (5) µm wide, ring organs and sensory pits not discernible; blade 41–51 (3) µm long, shorter than flagellum. Lauterborn organs virtually absent. Pecten epipharyngis consisting of 3 laminate platelets, laterally with 3–4 unequal teeth. Premandible 62–71, 68 µm long, bifid with prominent premandibular brush. Mandible 108–127, 115 µm long, with 1 large anterior, 1 dorsal and 2 inner teeth; seta subdentalis slender and well developed, distally straight; seta interna prominent; pecten mandibularis prominent and pointing towards teeth; 2 prominent sensillum minusculum. Mentum 90–106, 98 µm wide, with 8 pairs of teeth; median pair 17–21, 18 µm wide, which is longer than or subequal to second lateral tooth. First lateral tooth very short, shorter than third lateral, which is subequal to fourth; seventh tooth minute. Ventromental plate 83–97, 90 µm wide; distance between plates 18–38, 30 µm; median apices of plates pointing towards each other.

Abdomen. Procercus 7 (1) µm high. Posterior parapods 105 (1) µm long. Anal tubules 239 (1) µm long.

Remarks. One specimen from Ontario, Canada has a lower wing chaetotaxy. Cell m basal of RM with only 1 macrotrichium, r 4+5, m 1+2, m 3+4 and cu+an each with less than 80 macrotrichia, wing veins M 3+4, Cu, Cu 1, PCu and An each with less than 10 setae. The wing is also short, only 1.31 mm long. However, other measurements and the shape of the hypopygium are similar to the other specimens. The specimen is regarded as belonging to P. (Pe.) tritum , but not included in the above measurements.

Distribution. Widespread in the Holarctic Region.