Hexatoma (Eriocera) ussuriensis (Osten Sacken, 1860)

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 : 107-111

Hexatoma (Eriocera) ussuriensis (Osten Sacken, 1860)

( Figs. 39–53 )

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 3– 4 X length of lobe. Ventral spiracular lobes with thin dark median line apically, bifurcating into “Y”-shaped pattern proximally, the dorsal inner branch fused with its opposing sclerite. Mature larva medium sized, length about 22 mm Pupa with respiratory horns straight, apex flattened and rounded. Cephalic crest with four horns. Antennal sheath of male very long, almost reaching to tips of the legs. Antennal sheath of female shorter, reaching tips of wings.

Description. Length of last instar larvae— 19–24.5 mm, width— 2.5–3.5 mm. Body covered with long yellowish-brown hairs, which gives body golden color. Hairs on thorax are longer than on abdomen. The first and anterior part of tenth body segments are covered with longer hairs forming longitudinal rows. Posterior part of tenth segment is covered with shorter hairs forming short irregular transverse rows. Width and length of first and second thoracic segments are similar. Abdominal segments II–VIII are longer than wider. The last thoracic and the first abdominal segments are very short. There are small structures similar to spiracles on tergum of every segment. Last abdominal segment (anal) is constricted. It is covered with very long and dense setae, especially on the outer surface of spiracular lobes. 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. There is an area of longer setae between second and third setae ( Fig. 39 ).

Head capsule —2.0– 2.5 mm long and 0.7–0.9 mm wide. Overall structure similar to that of H (E.) californica except: one long seta on the anterior part of labrum ( Fig. 40 ) and saw-shaped lateral outgrooves ( Fig. 41 ); the first basal tooth of mandible is long, much longer than in other species ( Fig. 42 ); basal segment of antennae is three time as long as wide at base and on the top it has three very long setae ( Fig. 43 ).

Last segment. Spiracular field surrounded by four flattened elongate lobes ( Fig. 44 ). Dorsal lobe vestigial. Ventral lobe 1.5 times as long as lateral lobe. Lateral lobe almost 2.5 times as long as wide at the base. Ventral lobe almost three times as long as wide at the base. Apical part of each lateral and ventral lobe fringed with light brown long hairs, almost as long as lobes. Apex of ventral lobe with few darker and longer setae, three – four times as long as lobe. Outer margin of lateral lobe and vestigial dorsal lobe fringed with short light brown hairs. Lateral lobe with very narrow, stripe-shaped sclerite on inner margin of lobe, becomes slightly wider at the base. Ventral lobe with very narrow sclerite, becomes very wide at the base of lobe. Outer margin of ventral sclerite darker than inner. Inner branch fused with its opposing sclerite. Spiracles small, circular, widely separated; area between them more than 3X diameters of a spiracle. Inner circle of spiracle dark brown, outer ring is light brown.

Anus surrounded by four long, white, fleshy anal papillae ( Fig. 39 ). Lobes almost oval in shape and equal in size. Three long setae at the base of each ventral pair and two very long setae at the base of lateral pair ( Fig. 45 ).

Pupa. Male pupa is 20–21 mm long and 3.0– 3.5 mm wide. Female pupa is 17–22 mm long and 2.5–4.0 mm wide. Pupae of both sexes are 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 four unequal lobes in both sexes. Posterior (dorsal) lobe larger, trapezoid shaped with three long setae ( Figs. 46, 48 ). Anterior pair much smaller, horn-shaped with a single long seta near base. Antennal sheath in female short, only slightly longer than base of wing ( Fig. 48 ), male with very long antenna reaching posterior end of second abdominal segment ( Fig. 46 ). Two rows of spines on antenna visible throughout antennal sheaths in both sexes, more prominent in male. Tubercles on antennal scape and pedicel prominent, both segments enlarged. Clypeus with two small tubercles with long setae. Two prominent tubercles on trapezoid shaped labrum with triangular apex. Labial lobe diamond-shaped. Maxillary palp broad, transversal with small tubercles. Thorax: respiratory horns in male 1.1 mm long and 0.25 mm wide, less than half of head width; in female 1.0mm long and 0.2 mm wide, almost half of thorax width; minute annulations present along entire length of horn; in the middle respiratory horn getting wider, apex slightly flattened and rounded; horn dark brown with light brown base. Two small tubercles with two long setae each at the base of respiratory horn. Dorsum of thorax smooth. Apex of wing almost reaching the end of second abdominal segment in both sexes ( Figs. 46, 48 ). A small tubercle with two long setae at the base of wing. Legs reaching more than two thirds of the length of third abdominal segment in both sexes; hind pair slightly longer than other pairs ( Figs. 46, 48 ). Abdomen: segments II–VII with inconspicuous annuli, divide each abdominal segment into anterior and posterior parts. Length and width of both parts similar. Tergites and sternites on posterior part with transverse rows of small tubercles with long firm setae. Number of tubercles on tergites and sternites varies, usually more than 60 on both sides except segment VII. Sternites of segments II–III with two additional tubercles with two setae almost in the middle of posterior ring (at the level of spiracles). Female sternite of segment VII with two short transverse rows of spines interrupted by broad area. 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 and narrow. Ventral lobes (anal spines) small with rounded tips directed upward; tips of ventral lobes not reach the base of posterotergal spines and widely separated ( Fig. 46 ). Posterotergal spines very large, sharply pointed, directed upward with two setae in the middle of length. Anterodorsal and mediodorsal spines small, similar in shape and size, bear few setae on the tips ( Fig. 47 ), 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. Terminal segment of female elongate with very long and sharp sheaths of cerci and valves; both sheaths very close to each other ( Figs. 48, 49 ). Sheaths of cerci much longer than valves, directed upward and with few setae dorsally ( Fig. 50 ). Posterotergal spine single and more prominent than paired mediodorsal and anterodorsal spines. A small tubercle with long seta near the anterodorsal spine ( Fig. 50 ). A small tubercle with long seta situated on pleurite. A small tubercle with two long setae located on the middle of sternite.

Material examined. 14 larvae, 21 female and 16 male pupae, 9 female and 6 male pupal exuvia, 3 reared male and 3 reared females. MONGOLIA: 3 larvae and 1 female pupa from Selenge Aimag, Zuunburen Soum, Selenge Gol 7.8 km NW Zuunburen, N50.10285°, E105.78217°, elevation 647m, 5–6. VII. 2005, SRP 0 5070501, collected by V. Podeniene; 5 larvae, 2 male and 2 female pupal exuvia from Selenge Aimag, Khotol Soum, Orkhon Gol 15.0 km WNW Orkhon, N49.1633°, E105.18749°, elevation 756 m, 26–27. VII. 2005, SRP 0 5072602, collected by V. Podeniene; 1 larva, 2 female pupae, 3 male pupae, 7 female pupal exuvia, 4 male pupal exuvia and one reared male from Hovsgol Aimag, Ikh Uul Soum, Selenge Moron (river) ~ 8 km W Ikh-Uul; N49.44641°, E101.33625°, elevation 1069 m, 7–8. VII. 2006, SRP 0 6070701, collected by V. Podeniene; 2 reared males, 3 reared females, 18 female pupae, 13 male pupae and 5 larvae from Dornod Aimag, Bayan Uul Soum, Onon Gol, 0.5 km SW of Russian border, 2 km NW of Ulikhan Deed Ulikhan town, N49.51321°, E112.55703°, elevation 817 m, 20. VII. 2011, MAIS 2011072101, collected by V. Podeniene.

Habitat. Larvae of this species develop only in bottom of large and medium sized rivers. Last instar larvae and pupae can be found in riparian zone usually in gravel, sand or under stones ( Fig. 51 ).

Biological note. We found 4 female and 3 male Hexatoma ussuriensis pupae from Onon Gol, Dornad Aimag, with (presumably) parasitic Brachycera Cyclorrhapha (Anthomyidae?) larvae attached to the pupal body under the leg sheaths ( Figs. 52 , 53 ).

Figures

FIGURE 51. Habitat of larvae and pupae of Hexatoma (Eriocera) ussuriensis, Mongolia Dornod Aimag, Bayan Uul Soum, Onon Gol.

FIGURE 52. Parasitic Brachycera Cyclorrhapha (Anthomyidae?) larvae attached to the pupae of Hexatoma (Eriocera) ussuriensis.

FIGURE 53. Enlarged view of parasitic Brachycera Cyclorrhapha (Anthomyidae?) larva attached under sheats of legs of the pupa of Hexatoma (Eriocera) ussuriensis.

FIGURES 39 – 45 Hexatoma (Eriocera) ussuriensis. 39. Penultimate segment and terminal segment, ventral aspect. 40. Labrum, dorsal view. 41. Labrum and clypeus, dorsal view. 42. Right mandible, dorsal view. 43. Right antenna, dorsal view. 44. Spiracular field. 45. Penultimate segment and terminal segment of last instar larva, lateral aspect.

FIGURES 46 – 50. Hexatoma (Eriocera) ussuriensis. 46. General view of male pupa, lateral aspect. 47. General view of male pupa, dorsal aspect. 48. General view of female pupa, lateral aspect. 49. General view of female pupa, dorsal aspect. 50. Penultimate segment and terminal segment of female, lateral aspect.