Hexatoma (Hexatoma) nubeculosa (Burmeister, 1829)

Podeniene, Virginija & Gelhaus, Jon K., 2015, Review of the last instar larvae and pupae of Hexatoma (Eriocera) and Hexatoma (Hexatoma) (Diptera, Limoniidae, Limnophilinae), Zootaxa 4021 (1), pp. 93-118 : 112-115

Hexatoma (Hexatoma) nubeculosa (Burmeister, 1829)

Figs. (54–62)

Diagnosis. Larval and pupal characters as in genus and: larva with maxillary palps nearly 2X as long as mandible; spiracular lobes slender, marginal hair on lateral and ventral spiracular lobes of unequal length, ventral hairs much longer; apex of ventral lobes with a few extended darker setae, length 2X length of lobe. Ventral spiracular lobes with thin dark median line apically, bifurcating into “Y”-shaped pattern proximally, lines not meeting medially. Sclerites on ventral and lateral lobes of similar intensity, widest part of ventral sclerite over twice as wide as sclerite of lateral lobe. Mature larva medium sized, length about 20 mm. Pupa with respiratory horns straight, apex flattened and rounded. Cephalic crest with two horns. Ventral lobes (anal spines) of males enlarged, with rounded tips bent dorsally. Sheaths of cerci and valves of of female short.

Description. Length of last instar larvae— 19–23 mm; width— 1.8–2.5 mm. Body covered with short light brown hairs, which give body brownish-golden color. First and anterior part of tenth body segments are covered with longer hairs forming longitudinal rows. Hairs on tergum and sternum are longer than on pleurae. Posterior part of tenth segment is covered with shorter hairs forming short irregular transverse rows. Abdominal segments II–VIII are only slightly longer than wider. First abdominal segment and all thoracical segments are slightly shorter than wider. Last abdominal segment (anal) is constricted. Penultimate segment is distinctly inflated. There are four long stout setae on posterior end of sternite of penultimate segment, 1–2 and 3–4 setae are very close to each other.

Head capsule — 1.35–1.65 mm long and 0.85–9 mm wide. Overall structure similar to that of H (E.) californica except: anterior part of labrum with two cushions consisting of one long and one short setae, cushions very close to each other: only apical part of labrum covered with long setae ( Fig. 54 ); basal segment of antennae four time as long as wide at base; three setae on the top of antenna; the longest twice as long as apical papilla, the other two as long as apical papilla; two short sensory pegs at the base of apical papilla ( Fig. 55 ): all basal teeth of mandible differ in size and shape ( Fig. 56 ).

Last segment. Spiracular field surrounded by four flattened elongate lobes ( Fig. 57 ). Dorsal lobe vestigial. Ventral lobe is 1.5 times as long as lateral lobe. Lateral lobe almost twice as long as wide at the base. Ventral lobe almost three times as long as wide at the base. Apical part of each lobe fringed with light brown hairs. Length of lateral hairs on apical part of the lobe almost equal to the length of lobe, setae on apex of ventral lobe almost twice as long as ventral lobe. Outer margin of lateral lobe and vestigial dorsal lobe fringed with short hairs. Lateral pair with very narrow, dark, stripe-shaped sclerite on inner margin of lobe, becomes slightly wider at the base, apical part darker than basal part. Ventral pair with pale, narrow sclerite, bifurcates at the base of lobe (“Y” shaped sclerite). Both branches similar in size and shape. Spiracles small, circular, not widely separated, distance between them only more than 1.5X diameters of a spiracle. Inner circle of spiracle dark brown, outer ring light brown.

Anus surrounded by four short, white and fleshy anal papillae. Lobes almost oval-shaped and equal in size. Two long setae at the base of each lateral and ventral pair.

Pupa. Male pupa is 13.8–15.0 mm long and 2.0– 2.3 mm wide. Female pupa is 14–17 mm long and 2–2.3 mm wide. Pupae are yellowish brown. Head, thorax, wings and tergites of second and third abdominal segments are slightly darker than the rest of the body. Head: cephalic crest prominent, with wrinkled surface, consists of two horn-shaped lobes. Three long setae at base on dorsal side and one seta at the base on ventral side ( Fig. 60 ). Antennal sheaths in both sexes very short, reaching just base of wing ( Figs. 58, 59 ). A large horn-shaped tubercle on the scape of antenna. Basal segments of antenna not enlarged. Two prominent horn-shaped tubercles on labrum ( Fig. 60 ). Labial lobe diamond-shaped. Maxillary palp broad, transversal with small tubercles. Thorax: respiratory horns in both male and female very short, less than one-fourth as long as head’s width; minute annulations along entire length of horn; apex of horn slightly flattened and rounded ( Fig. 60 ). Respiratory horns reach just to base of cephalic crest. Dorsum of thorax smooth. Apex of wing almost reaching the end of second abdominal segment ( Figs. 58, 59 ). A small tubercle with two very short setae at the base of wing. Legs reaching more than half of the length of third abdominal segment; hind pair noticeably longer than others. Hind legs reach transversal row of spines on sternite of third abdominal segment ( Figs. 58, 59 ). Abdomen: segments II–VII bear well defined annuli, each abdominal segment into two parts; anterior part narrower than posterior. Length of both parts similar, except segment VII. Tergites and sternites on posterior part with transverse rows of small tubercles with few setae. Number of tubercles on dorsal and ventral parts varies, usually more than 30 on both sides (except segment VII). Sternites of segments III–VII with two short transverse rows of spines interrupted by broad area. Prominent spiracles almost in the middle of pleurites of abdominal segments II–VII. Slightly near dorsal margin of spiracles situated two setae. A small tubercle with a single seta on the middle of anterior part of pleurite of segments III–VII. Terminal segment of male blunt and narrow ( Fig. 61 ). Ventral lobes (anal spines) enlarged, with rounded tips bent dorsally and noticeably separated from the rest of terminal segment; apical part of ventral lobes almost reaches posterotergal spines ( Figs. 58, 61 ). Posterotergal spines very small, blunt (hardly visible) in some specimens, but very well developed spines with acute tips in other specimens. Anterodorsal and mediodorsal spines small; similar in shape and size with few setae on the tips ( Fig. 61 ), situated almost in the middle of tergum of terminal segment. A small tubercle in between of mediodorsal and posterotergal spines. A small tubercle near the anterodorsal spine. A prominent tubercle with two long setae situated on the pleurite. Sheaths of cerci and valves of terminal segment of female short. Sheath of cerci tapering to the acute tip, directed upward. A short seta on the apex of cerci. Cerci widely separated (from dorsal point of view). Valves close to each other (from ventral point of view). Cerci and valves widely separated ( Figs. 59, 61 ). Posterotergal spine single, more prominent than paired mediodorsal and anterodorsal spines. A small tubercle with few long setae located near the anterodorsal spine ( Fig. 62 ). A large rounded tubercle situated on pleurite.

Material examined. This species is reported new for Mongolia. 37 last and younger instar larvae, 10 male and 5 female pupae and 1 reared male. MONGOLIA: 14 larvae from Selenge Aimag, Tushig Soum, Zelter Gol near Zelter, N50.35162°, E105.04436°, elevation 736 m, 26. VII. 2003, SRP 0 4072601, collected by V. Podeniene; 6 larvae and 2 male pupae from Ovorkhangay Aimag, Bat-Olzyi Soum, Orkhon Gol ~ 34 km W of Khujirt, N46.89303°, E102.39457°, elevation 1610 m, 0 6. VII. 2004, SRP 0 4070602, collected by V. Podeniene; 6 larvae from Zavkhan Aimag, Ikh-Uul Soum, Ideriin Gol ~ 28 km E of Tosontsengel, N48.71968°, E98.65184°, elev. 1654 m, 19–20. VII. 2004, SRP 0 4071903, collected by V. Podeniene; 1 larva from Selenge Aimag, Buruunharaa Soum, Haraa Gol 2.3 km S of Bayangol, N48.87738°, E106.12375°, elevation 807 m, 04–05. VII. 2005 SRP, 0 5070402, collected by V. Podeniene; 10 larvae, 8 male and 5 female pupae and 1 reared male from Bayan Olgyi Aimag, Bulgan Soum, Bulgan Gol ~ 20 km S of Bulgan, N46.78006°, E091.30396°, elevation 1801 m, 09.VII.2009, MAIS 2009070901, collected by V. Podeniene.

Habitat. Larvae of this species develop only in bottom sand or gravel of large and medium sized rivers. Last instar larvae and pupae can be found in riparian zone usually in gravel or sand.

Figures

FIGURES 54 – 57. Hexatoma (Hexatoma) nubeculosa. 54. Labrum and clypeus, dorsal view. 55. Right mandible, dorsal view. 56. Right antenna, dorsal view. 57. Spiracular field.

FIGURES 58 – 62. Hexatoma (Hexatoma) nubeculosa. 58. General view of male pupa, lateral aspect. 59. General view of female pupa, lateral aspect. 60. Head of male pupa, ventral aspect. 61. Terminal segment of male pupa, dorsal aspect. 62. Terminal segment of female pupa, lateral aspect.