Hexatoma (Eriocera) sachalinensis (Alexander, 1924)

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 : 102

Hexatoma (Eriocera) sachalinensis (Alexander, 1924)

( Figs. 21–28 )

Diagnosis. Larval characters as in genus and: larva with spiracular lobes slender, marginal hair on lateral and ventral spiracular lobes of similar length, without extended darker setae at ventral lobe apex. Maxillary palp as long as mandible. Ventral spiracular lobes with thin dark median line apically, bifurcating into “Y”-shaped pattern proximally, lines not meeting medially. Mature larva large, length 30–40 mm long. Pupa unknown.

Description. Length of last instar larvae— 31–41 mm; width— 4.5–5 mm. Body covered with very short yellowish-brown hairs, giving body golden color. First and anterior part of tenth body segments with longer hairs forming longitudinal rows. Posterior part of tenth segment with shorter hairs forming long regular transverse rows. All thoracic and abdominal segments II–VIII slightly longer than wider. First abdominal segment short. 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, equidistant from each other.

Head capsule — 4 mm long, 1.85 mm wide. Elongate-oval in shape, depressed dorsoventrally and much reduced, especially ventral side ( Fig. 21 ). Medial labrum border low, broadly rounded, with a lateral fleshy, short and broad lobe scarsy covered with setae ( Figs. 22, 23 ). Long and short setae on anterior part of labrum, a prominent tubercle with sensory pegs located nearby these setae. Few short sensory structures nearby posteriorlateral side of labrum ( Fig. 22 ). Clypeus distinctly divided from labrum. Clypeus diamond-shaped with posterior part broadly rounded, slightly sclerotized. Frons separated from clypeus, divided into two large rectangular lateral plates. Basal segment of antenna cylindrical with upper part directed outward ( Fig. 25 ), basal segment of antenna four times as long as wide, with two short and single long setae on the apical part. Apical segment short, sculptured. Mandible sickle-shaped, with a single sharp, curved apical tooth ( Fig. 4 ), three small teeth at the base, second tooth well developed, the first and the third teeth inconspicuous ( Fig. 24 ). Inner and outer parts of maxilla fused. Maxilla short, almost the same length as mandible; apical part membranous, without short setae ( Fig. 21 ). Cardo reduced into very small sclerite. Hypopharyngeal part of head capsule membranous. Posterior part of head capsule consists of one pair of rod-shaped internolateralia and one pair of rod-shaped externolateralia. Externolateralia (lateral rods) less sclerotized than internolateralia, bent inwards. Internolateralia (dorsal rods) straight and diagonal until midlenght, then medial (inner) margins divergent ( Fig. 21 ).

Last segment. Spiracular field surrounded by four flattened elongate lobes ( Fig. 26 ). 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 dark brown hairs as long as lobes. Outer margin of lateral lobe and vestigial dorsal lobe fringed with short hairs. Lateral lobe bears very narrow, dark, line (sclerite) on inner margin of lobe, slightly wider at the base. Ventral lobe with very dark, narrow line (sclerite), bifurcating at base of lobe (“Y” shaped sclerite). Both branches similar in size and shape. Spiracles small, circular and widely separated; distance between them more than 3X diameters of a spiracle. Inner circle of spiracle dark brown, outer ring light brown.

Anus surrounded by four long, white, fleshy anal papillae ( Fig. 27 ). Lobes almost cone-shaped, equal in size. Two long setae at the base of each lateral and ventral pair ( Fig. 28 ).

Pupa. Unknown.

Material examined. This species is reported new for Mongolia. 7 larvae. MONGOLIA: 3 larvae from Bulgan Aimag, Teshig Soum, main branch of Tariankhtain Gol, just upstream of confluence with Egiin Gol, N49.70766°, E103.10295°, elevation 911m, 10.VII.2005, SRP 05071001 a, collected by V. Podeniene; 2 larvae from Bulgan Aimag, Bugat Soum, Altat Gol 35.2 km SW of Khutag-Ondor, N49.21674°, E103.10725°, elevation 1020m, 26.VII.2005, SRP 0 5072601, collected by V. Podeniene; 2 larvae from Uvs Aimag, Davst Soum, Tokhilog Gol 4 km N of Mongolian military border outpost, N50.71740°, E092.59928°, elevation 1043 m, 14–15.VII.2010, MAIS 2010071402, collected by V. Podeniene.

Habitat. Larvae of this species develop in bottom gravel of large and medium sized rivers.

Figures

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.

FIGURES 1 – 5. Hexatoma (Eriocera) californica. 1. General view of head capsule of last instar larva, dorsal aspect. 2. Labrum and clypeus, dorsal aspect. 3. Right mandible, dorsal view. 4. Right antenna, dorsal view. 5. Spiracular field.