Hexatoma (Eriocera) stackelbergi Alexander, 1933

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 : 104-107

Hexatoma (Eriocera) stackelbergi Alexander, 1933

( Figs. 29–38 )

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, and similar width at widest point. Mature larva medium sized, length about 20 mm. Pupa with cephalic crest with two horns. Pupal leg sheaths reaching middle of third sternite.

Description. Length of last instar larvae— 19–21 mm; width— 1.8–2.5 mm. Body covered with short light brown hairs, giving body brownish-golden color. First and anterior part of tenth body segments covered with longer hairs forming longitudinal rows. Hairs on tergum and sternum longer than that on pleurae. Posterior part of tenth segment covered with shorter hair forming short irregular transverse rows. Abdominal segments II–VIII longer than wider. First abdominal segment and all thoracic segments slightly shorter than wider. Small structures similar to spiracles on tergum of every segment. Last abdominal segment (anal) constricted. Penultimate segment distinctly inflated. Four long stout setae on posterior end of sternite of penultimate segment, 1–2 and 3–4 setae very close to each other. Area of longer hairs between second and third setae ( Fig. 29 ).

Head capsule — 1.50–1.65 mm long, 0.85–9 mm wide. Overall structure similar to that of H (E.) californica except: anterior part of labrum with one long and one short seta; apical part of labrum covered with long setae; posterior part of clypeus broadly rounded ( Fig. 30 ); all basal teeth of mandible differ in size and shape ( Fig. 31 ); basal segment of antennae four times as long as wide at base; three setae on apex of antenna; the longest twice as long as apical papilla, the other two as long as apical papilla; two short sensory pegs located at the base of apical papilla ( Fig. 32 ).

Last segment. Spiracular field surrounded by four flattened elongate lobes ( Fig. 33 ). Dorsal lobe vestigial. Ventral lobe 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. Lateral hairs almost as long as lobe, ventral hairs almost twice as long as ventral lobe. Apex of ventral lobe with few longer setae, almost twice as long as lobe. Outer margin of lateral lobe and vestigial dorsal lobe fringed with short hairs. Lateral pair with very narrow, pale, stripe-shaped sclerite on inner margin of lobe, slightly wider at the base. Ventral pair with pale, narrow sclerite, bifurcated at 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, fleshy anal papillae ( Fig. 28 ). Lobes oval-shaped, equal in size. Two long setae at the base of each lateral and ventral pair.

Pupa. Male pupa 20 mm long and 3.5 mm wide. Pupa yellowish brown. Head, thorax, wings and tergites of abdominal segments second and third slightly darker than rest of the body. Head: cephalic crest prominent, with wrinkled surface; with four unequal lobes. Posterior (dorsal) lobe larger, trapezoidal in shape with three long setae ( Fig. 34 ). Anterior pair much smaller, horn-shaped with a single long seta near base. Antennal sheaths in male very long reaching posterior end of second abdominal segment ( Fig. 35 ). Tubercles on antennal scape and pedicel prominent. Both segments strongly enlarged ( Fig. 34 ). Clypeus has two small tubercles bearing long setae. Two prominent tubercles on labrum. Labrum trapezoid shaped with triangular apex ( Fig. 34 ). Labial lobes diamondshaped. Maxillary palp broad, transversal and bearing small tubercles ( Fig. 34 ). Thorax: respiratory horns in male 1.1 mm long, 0.25 mm wide, less than half head width; minute annulations present along entire length of horn; respiratory horn widest in the middle, apex slightly flattened and rounded, base light brown, remainder dark brown ( Fig. 34 ). Two small tubercles with two long setae at the base of respiratory horn. Dorsum of thorax smooth. Apex of wing almost reaching the end of second abdominal segment ( Figs. 35–36 ). A small tubercle with two long setae at the base of wing. Legs reach slightly more than half length of third abdominal segment; hind pair distinctly longer than other pairs. All legs not reach transversal row of spines on sternite of abdominal segment III ( Fig. 35 ). Abdomen: segments II–VII bear well defined annuli, divide each abdominal segment into two parts; anterior part distinctly narrower than posterior (length of both parts equal), except segment VII ( Fig. 35 ). Tergites and sternites on posterior part with transverse rows of small tubercles with long firm setae. Number of tubercles on dorsum and venter varies, usually with more than 60 on both (except segment VII). Sternites of second and third segments with two additional tubercles with two setae almost in the middle of posterior ring (at the level of spiracles). Sternite of segment VII with two short transverse rows of spines interrupted by broad area (fig. 37). Prominent spiracles almost in the middle of pleurites of abdominal segments III–VII. Slightly near dorsal margin of spiracles situated two setae. A small tubercle with a single seta on the middle of anterior part of segments III–VII. Terminal segment of male blunt, narrow ( Fig. 38 ). Ventral lobes (anal spines) well developed, middle-sized with rounded tips directed dorsally and distinctly separated from rest of terminal segment ( Fig. 36 ). Posterotergal spines very large, sharp pointed, directed upward, bearing two setae in the middle of length. Anterodorsal and mediodorsal spines small, similar in shape and size with few setae on the apices ( Fig. 38 ), situated almost in the middle of tergum of terminal segment. A small tubercle in between of mediodorsal and posterotergal spines. A small tubercle with long seta near the anterodorsal spine. A prominent tubercle with two long setae situated on the pleurite. Two prominent tubercles with four setae on the middle of sternite of terminal segment.

Material examined. This species is reported new for Mongolia.

22 last and younger instar larvae, 1 male pupa, and 1 reared male. MONGOLIA: 5 larvae from Arkhangay Aimag, Ikhtamir Soum, Khoit Tamir Gol ~ 29 km SW of Ikhtamir, N47.48567°, E100.87875°, elevation 1749 m, 15. VII. 2004, SRP 0 4071501, collected by V. Podeniene; 4 larvae from Zavkhan Aimag, Tosontsengel Soum, Delgarakhiin Gol ~ 16 km S of Tosontsengel, N48.61518°, E98.23096°, elevation 1761 m, 20–21. VII. 2004, SRP 0 4072001, collected by V. Podeniene; 10 larvae, 1 male pupa and 1 reared male from Zavkhan Aimag, Ider Soum, Ideriin Gol ~ 4 km NE of Zuunmod/Ider, N48.24995°, E97.40627°, elev. 1929 m, 22–23. VII. 2004, SRP 0 4072203, collected by V. Podeniene; 3 larvae from Hovsgol Aimag, Chandmani-Ondor Soum, Khalkhan Gol 19.8 km E of Chandmani-Ondor, N50.51523°, E101.21074°, elevation 1220 m, 17–18. VII. 2005, SRP 05071702 a, collected by V. Podeniene.

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

Figures

FIGURES 29 – 33. Hexatoma (Eriocera) stackelbergi. 29. Penultimate segment and terminal segment, ventral aspect. 30. Labrum and clypeus, dorsal view. 31. Right mandible, dorsal view. 32. Right antenna, dorsal view. 33. Spiracular field.

FIGURES 34 – 38. Hexatoma (Eriocera) stackelbergi. 34. Head of male pupa, ventral aspect. 35. General view of male pupa, ventral aspect. 36. General view of male pupa, lateral aspect. 37. General view of male pupa, dorsal aspect. 38. Terminal segment of male pupa, dorsal aspect.

FIGURES 21 – 28. Hexatoma (Eriocera) sachalinensis. 21. General view of head capsule of last instar larva, dorsal aspect. 22. Labrum, dorsal view. 23. Labrum and clypeus, dorsal view. 24. Right mandible, dorsal view. 25. Right antenna, dorsal view. 26. Spiracular field. 27. Penultimate segment and terminal segment, ventral aspect. 28. Penultimate segment and terminal segment, lateral aspect.