Ora depressa (Fabricius, 1801)

Libonatti, María L., Jorge, Gabrielle, Archangelsky, Miguel & Michat, Mariano C., 2018, The last instar larva and pupa of Ora depressa (Coleoptera: Scirtidae), a marsh beetle with underwater pupation, Acta Entomologica Musei Nationalis Pragae 58 (2), pp. 441-455 : 443-450

Ora depressa (Fabricius, 1801)

Material examined. ARGENTINA: ENTRE RÍOS PROVINCE: Pre-Delta National Park: Las Piedras pond, 19–21.iii.2012, coll. M. L. Libonatti: 1 ♁ (with last instar larval and pupal exuviae), 2 ♀♀ (with larval and pupal exuviae), 4 pupae (with last instar larval exuviae), 2 pupal exuviae, 3 last instar larvae, 4 early instar larvae, 4 larval exuviae. ARGENTINA: MISIONES PROVINCE: Antonia Ramos Research Centre:El Tajamar pond, 18.xi.2013, coll. M. L. Libonatti: 1 ♁ (with last instar larval and pupal exuviae), 1 last instar larva.

Description. Last instar larva. Body ( Fig 1 ) broadly elliptical; length about 11 mm in fully expanded specimen. Color. Body brownish testaceous; head with a relatively large elongate oval brown spot next to each frontal line and several clusters of smaller brown spots on frontale and posterior part of parietale; dorsal surface of thorax and abdomen (except uniformly brown segments 8 and 9) with many small brown spots and a transverse row of several larger brown spots in the middle of each thoracic segment and near anterior margin of each abdominal segment; ventral surface and legs testaceous.

Head ( Figs 3–7 ). Head capsule transverse, broadly bowl-shaped, 1.8× as wide as long, with one stemma on each side behind antenna. Frontale with numerous grooved scale-like setae over whole surface and 16 other sensilla situated as follows. Anterolateral portions between the antennal socket and the frontoclypeal suture each with a transverse row of one pore-like sensillum, two short hairlike setae and one long hair-like seta. Anterior third with a transverse row of four club-like setae and two pore-like sensilla posterior to the row. Middle portion with two club-like setae. Lateral portion of each parietale with 4–5 very long hair-like setae and many spine-like setae. Dorsal surface of each parietale with numerous grooved scale-like setae on inner portion near frontal line and 14 other sensilla situated as follows. Anterolateral portion behind stemma with one short hair-like seta, one ungrooved scale-like seta, one pore-like sensillum and one club-like seta. Anterior portion at frontal line with one long hair-like seta. Middle portion at frontal line with one ungrooved scale-like seta, one pore-like sensillum, one short hair-like seta and one club-like seta. One club-like seta situated halfway between the club-like seta behind the stemma and the club-like seta at frontal line. Posterior portion with an irregular longitudinal row of four short hair-like setae. Area behind stemmata with several minute spinulae.

Antennae ( Figs 8–9 ). Scape short, curved outwards, with several strong setae. Pedicel straight, approximately 1.5× as long as scape, with one sensorium at apex, sensorium 0.4× as long as pedicel. Flagellum broken on specimens examined.

Clypeolabrum ( Figs 10–13 ) broadly vase-shaped, lobes well-developed, as long as wide, well-separated. Dorsal surface of each lobe with a simple, strong seta (spine of HANNAPPEL & PAULUS 1991) situated on a small apical elevation, a pore-like sensillum in middle portion and many long hair-like setae of varying length on outer margin. Anterior portion of clypeolabrum including inner dorsal portions of lobes with a dense band of numerous, strong palisade setae, with bases almost confluent, interrupted in the middle by a bifid seta. Each side of clypeolabrum posterior to the palisade setae with an irregular oblique row of 5–6 basal setae, not clearly differentiated from smaller hair-like setae of lobes and from outer palisade setae. Rest of dorsal surface of clypeolabrum with numerous grooved scale-like setae, several short hair-like setae and two pore-like sensilla in middle portion. Frontal surface of clypeolabrum bearing, from dorsal to ventral, a pair of short hair-like setae (sensory ciliae of HANNAPPEL & PAULUS 1991), a pair of pore-like sensilla (campaniform sensilla of HANNAPPEL & PAULUS 1991), a transverse row of fine microtrichia and two lateral groups of three pore-like sensilla each above the cone teeth (the outermost being a depression of the cuticle; the two innermost being conical elevations of the cuticle). Ventral surface of each lobe with five inner setae, innermost the shortest. Epipharynx as described for the family ( HANNAPPEL & PAULUS 1987).

Mandibles ( Figs 14–16 ) with obtuse tip. Dorsal surface with a few short hair-like setae and numerous short microtrichia on basal portion. Ventral surface with two bristle-fields: one small, located near apex, consisting of a tuft of pectinate and branched bristles; the other larger, extended along inner margin, consisting of only branched bristles. Outer margin with a row of 16–17 long hair-like setae.

Maxillae ( Figs 17–24 ). Galea with dense field of stalk comb-bristles. Lacinia with 7–8 teeth. Maxillary palpus elongate, four-segmented. Palpomere 1 stout, with many hair-like setae of varying length and some pore-like sensilla. Palpomere 2 slightly shorter than palpomere 1, with some very short hair-like setae, several pore-like sensilla and one long hair-like seta in about the middle of dorsal surface. Palpomere 3 the longest, slightly longer than palpomere 2; dorsal surface with a few ungrouped sensory organs; ventral surface with many sensory organs grouped in an elongate area. Palpomere 4 0.85× as long as palpomere 3; dorsal surface with many ungrouped sensory organs, lateral surface with one subapical digitiform sensillum; ventral surface with a few ungrouped sensory organs and three groups of sensory organs.

Labium ( Figs 25–26 ) broadly hexagonal; posterior portion with several grooved scale-like setae and two long hair-like setae; anterior portion with several hair-like setae of varying length; lateral margins with several long hair-like setae. Labial palpus two-segmented. Palpomere 2 about 1.5× as long as palpomere 1; apex with one grooved conical basiconic sensillum, one elongate basiconic sensillum, three styloconic sensilla and two coeloconic sensilla.

Hypopharynx ( Figs 27–31 ) slightly longer than wide. Stiff plate bearing a few hair-like setae on ventral surface and a dense fringe of multifid setae on frontal margin. Socket and keel sclerites contiguous. Socket bristles with a very large apical tooth and 2–6 smaller teeth located on basal half of inner margin. Keel bristles with 6–10 teeth distributed along inner margin. Keel sclerite with a transverse row of four pore-like sensilla situated anteriorly and a transverse row of two pore-like sensilla situated more posteriorly. Each side of hypopharynx with 5–6 comb teeth, innermost the widest, with pointed apex, remaining ones with obtuse apex. Sclerite connecting inner pair of comb teeth present, composed of two hand-like structures (each structure with 4–6 fingers). Each side of hypopharynx with a row of 24–30 long, strong, curved claw teeth; at least one outer row of numerous, very short, subtle claw teeth. Cushion area closed anteriorly, round.

Thorax ( Figs 1 , 32–35 ) widest at metanotum, almost 2× as wide as head capsule. Lateral margins each with a row of several spine-like setae and numerous long hair-like setae of variable length. Numerous grooved scale-like setae over whole dorsal surface and few short hair-like setae near anterior margin of each tergite. Pronotum with 26 other setae on each half situated in three irregular transverse rows. Anterior row with three club-like setae, three ungrooved scale-like setae and one long hair-like seta. Middle row with one long hair-like seta, seven ungrooved scale-like setae and two club-like setae. Posterior row with four ungrooved scale-like setae, one long hair-like seta and four club-like setae. Mesonotum with 20 other setae on each half situated in two irregular transverse rows. Anterior row with 11 club-like setae. Posterior row with two long hair-like setae, six ungrooved scale-like setae and one club-like seta. Metanotum with 25 other setae on each half situated in two irregular transverse rows. Anterior row with 14 club-like setae. Posterior row with eight ungrooved scale-like setae, one long hair-like seta and two club-like setae.

Legs ( Figs 36–38 ) relatively long. Posterior surface of femur and tibiotarsus with a row of long hair-like (natatorial) setae near dorsal margin. Claw with two setae in middle, anterior seta 2× as long as posterior seta, ventral edge behind setae with a row of spinulae. Tibiotarsus of prothoracic leg with a row of pectinate setae along posterior margin; tibiotarsal organ well-developed, composed of small setae with widened feather-like distal portion.

Abdomen ( Figs 1 , 39–45 ) slightly narrower than thorax, gently tapered posteriorly. Tergites 1–7 each with numerous grooved scale-like setae over whole surface, two irregular transverse rows of several club-like setae, a transverse row of six long hair-like setae near posterior margin, several ungrooved scale-like setae situated on posterolateral corners, and a longitudinal row of spine-like setae near each lateral margin. Posterior margin of tergites 6–7 with a transverse row of spine-like setae. Tergite 8 elongate trapezoid; posterior margin concave. Dorsal surface densely covered with grooved scale-like setae. Middle portion with an irregular transverse row consisting of two ungrooved scale-like setae and four long hair-like setae. One pair of pore-like sensilla situated halfway between the row mentioned above and the posterior margin. Posterior portion with several very short hair-like setae and two long hair-like setae. Lateral margins each with a row of 5–6 very long hair-like setae intermixed with 3–8 spine-like setae; three shorter hair-like setae situated posteriorly. Tergite 9 arch-shaped; anterodorsal margin produced medially. Anteroventral margin with simple and bifid setae, both with serrate edges. Lateral margins each with a row of several hair-like setae of variable length. Posterior margin with one long hair-like seta on each lateral corner and four minute setae between them. Sternites 1–7 each with numerous hair-like setae over whole surface, longer near lateral and posterior margins, and a longitudinal row of spine-like setae near each lateral margin. Posterior margin of sternites 6–7 with an additional transverse row of spine-like setae. Sternite 8 wide trapezoid, densely covered with long hair-like setae. Sternite 9 semioval, middle portion with many grooved scale-like setae and several long hair-like setae, posterior margin with bipectinate setae. Five simple anal papillae.

Pupa. Body ( Figs 46–48 ). Length about 5.5 mm. Body brown, with several small testaceous spots on abdomen, abdominal ventrite 7 testaceous. Head, dorsal surface of thorax, elytra, and femora densely covered with long setae.

Thorax ( Figs 49–50 , 53–55 ) Pronotum lacking horns (spines of YOSHITOMI 2005), widely expanded laterally, with a row of microtrichia along each lateral margin and a dense tuft of very long pectinate setae on anterolateral corners.Anteroventral part of pterothecae with a dense tuft of very long pectinate setae, similar to that on pronotum. The row of microtrichia together with both dense tufts of setae form an hydrophobic setation that covers the edges of the lateral pronotal expansions ( Fig. 53 ).

Abdomen ( Figs 51–52 , 56–58 ). Ventrites 1–6 with an irregular transverse row of long setae on dorsal surface, an irregular transverse row of long setae on ventral surface, and a longitudinal row of long setae along lateral margins. Ventrite 7 without setae. Sexual dimorphism present: male attachment organ consisting of a square base and a pair of processes each with pointed apex, covered with short teeth; female attachment organ consisting of a triangular base, a pair of processes each with widened apex, covered with longer teeth, and an additional small rounded process situated basally between the pair of processes.

Biology. Larvae were collected from a flooded area adjacent to Las Piedras pond (Pre-Delta National Park, Entre Ríos Province), mainly dominated by the plant species Polygonum punctatum Elliott, 1817 and Thalia geniculata Linnaeus, 1753 (Fig. 69), and from marginal areas of El Tajamar pond (CIAR, Misiones Province), dominated by Juncaceae and Poaceae . Both ponds are natural and exposed to sun. Several exuviae of pupae were also found in the field. The rearing of the larvae allowed us to observe that pupae are aquatic; they hang from the water’s surface. The exuviae of the last instar larva remains attached to the pupa during pupation. Pupae make abdominal movements when disturbed. Pupal period is one day under laboratory conditions. Adults emerge in the evening or night.

Figures

Figs 1–2. Habitus of Ora depressa (Fabricius, 1801), dorsal aspect. 1 – last instar larva. 2 – male adult. Scale bars = 1 mm.

Figs 3–7. Head morphology and chaetotaxy of the last instar larva of Ora depressa (Fabricius, 1801). 3 – head capsule, dorsal aspect, showing long hair-like setae (squares with a cross), short hair-like setae (squares with dot), club-like setae (squares), ungrooved scale-like setae (circles with dot), and pore-like sensilla (circles); FR = frontale; PA = parietale. 4 – close-up of the square area indicated in figure 3. 5 – close-up of the rectangular area indicated in figure 3. 6 – club-like seta. 7 – grooved scale-like seta. Scale bars: 3 = 0.5 mm; 4 = 0.05 mm; 5–7 = 0.01 mm.

Figs 8–9.Antenna of the last instar larva of Ora species.8 – right antenna of Ora depressa (Fabricius, 1801), dorsal aspect. 9 – antennal sensorium of Ora sp. Scale bars = 0.1 mm.

Figs 10–13. Clypeolabrum of the last instar larva of Ora depressa (Fabricius, 1801). 10 – dorsal aspect. 11 – close-up of left lobe, ventral aspect. 12 – ventral aspect. 13 – close-up of frontal margin. Scale bars: 10, 12 = 0.2 mm; 11, 13 = 0.1 mm.

Figs 14–16. Mandible of the last instar larva of Ora depressa (Fabricius, 1801). 14 – ventral aspect. 15 – close-up of the rectangular area indicated in figure 14. 16 – close-up of the rectangular area indicated in figure 14 in dorsal aspect. Scale bar: 0.2 mm.

Figs 17–24. Maxilla of the last instar larva of Ora species. 17 – right maxilla of O. depressa (Fabricius, 1801), ventral aspect. 18 – laciniar teeth of O. depressa. 19 – close-up of the rectangular area indicated in figure 17, showing the stalk comb-bristles of the basal portion of galea. 20 – close-up of the rectangular area indicated in figure 17, showing the stalk comb-bristles of the apical portion of galea. 21 – right maxillary palpus of O. depressa, ventral aspect. 22 – right maxillary palpus of O. depressa, dorsolateral aspect. 23 – close-up of the apical portion of the maxillary palpus of O. depressa. 24 – digitiform sensillum of Ora sp. Scale bars: 17, 21–22 = 0.2 mm; 18–20, 23 = 0.02 mm; 24 = 0.01 mm.

Figs 25–27. Labium of the last instar larva of Ora depressa (Fabricius, 1801). 25 – labium, ventral aspect. 26 – close-up of the apical portion of right palpus, showing conical basiconic sensillum (Conical B), elongate basiconic sensillum (Elongate B), styloconic sensilla (S), and coeloconic sensilla (C). 27 – close-up of the rectangular area indicated in figure 25, showing the multifid setae of stiff plate (hypopharynx). Scale bars: 25 = 0.2 mm; 26 = 0.002 mm; 27 = 0.01 mm.

Figs 32–35. Thorax of the last instar larva of Ora depressa (Fabricius, 1801), dorsal aspect, showing long hair-like setae (squares with a cross), club-like setae (squares), ungrooved scale-like setae (circles with dot), and pore-like sensilla (circles). 32 – pronotum. 33 – mesonotum. 34 – metanotum. 35 – close-up of several grooved scale-like setae and one club-like seta of thorax. Scale bars: 32–34 = 0.5 mm; 35 = 0.02 mm.

Figs 36–38. Leg of the last instar larva of Ora depressa (Fabricius, 1801). 36 – prothoracic leg. 37 – tibiotarsus and pretarsus of prothoracic leg. 38 – close-up of tibiotarsal organ. Scale bars: 36 = 0.5 mm; 37 = 0.1 mm; 38 = 0.01 mm.

Figs 39–45. Abdomen of the last instar larva of Ora depressa (Fabricius, 1801). 39 – close-up of the chaetotaxy of tergites 1–7. 40 – close-up of the chaetotaxy of sternites 1–7. 41 – tergite 8, dorsal aspect. 42 – tergite 9, ventral aspect. 43 – sternite 8, ventral aspect. 44 – sternite 9, ventral aspect. 45 – marginal seta of sternite 9. Scale bars: 39 = 0.02 mm; 40 = 0.1 mm; 41–44 = 0.5 mm; 45 = 0.003 mm.

Figs. 46–48. Habitus of the pupa of Ora depressa (Fabricius, 1801). 46 – dorsal aspect. 47 – lateral aspect. 48 – ventral aspect. Scale bar = 1.0 mm.

Figs 49–52. Pupa of Ora depressa (Fabricius, 1801), dorsal aspect. 49 – thorax. 50–51 – close-ups of the rectangular area indicated in figure 49. 52 – close-up of abdomen. Scale bars: 49 = 0.5 mm; 50–52 = 0.2 mm.

Figs 53–58. Pupa of Ora depressa (Fabricius, 1801), ventral aspect. 53 – left side of head and prothorax. 54 – close-up of the rectangular area indicated in figure 53. 55 – close-up of the rectangular area indicated in figure 54. 56 – female attachment organ. 57 – terminal portion of the abdomen of male. 58 – close-up of male attachment organ. Scale bars: 53 = 0.5 mm; 54, 56–57 = 0.2 mm; 55, 58 = 0.05 mm.