Tropisternus (Pristoternus) ovalis Castelnau, 1840

Torres, Patricia L. M., Michat, Mariano C., Archangelsky, Miguel & Fernández, Liliana A., 2014, Description of immatures of the genus Tropisternus Solier, subgenus Pristoternus Orchymont (Coleoptera: Hydrophilidae), with emphasis on the chaetotaxy and morphometry of larval forms, Zootaxa 3790 (2), pp. 380-398 : 388-392

Tropisternus (Pristoternus) ovalis Castelnau, 1840

( Figs. 3 , 20–31 )

Material examined. Three egg cases, 8 larvae of instar I, 3 of instar II, 4 of instar III and 2 pupae were used for the descriptions. Breeding adults were collected at the following locality: Argentina: Corrientes Province, Mburucuyá National Park, I-2008 (see Fig. 1 in Torres et al. 2012).

Description, egg case ( Fig. 3 ). Whitish, saccular, subcircular in cross section. Mast absent. Length = 3.7–3.9 mm, width = 3.5–3.7 mm, height = 2.6–2.8 mm; cap length = 2.2–2.5 mm.

Description, instar I ( Figs. 22–31 ). Color: head capsule testaceous, with yellowish areas around frontal sulci and on dorsolateral surface of parietale. Cephalic and thoracic appendages testaceous. Thoracic tergites testaceous with yellowish scattered maculae; thoracic sternites testaceous. Body: for morphometric measurements and ratios see Table 2 . Head capsule ( Figs. 22–24 ): nasale with 7–8 teeth on anterior margin, without anteroventral denticles ( Fig. 24 ). Mandibles ( Figs. 27–28 ): distal tooth of retinaculum bifid or unifid apically, outer lateral surface slightly serrate. Labium ( Figs. 25–26 ): anterolateral angles of mentum strongly projected forward. Dorsal surface of mentum with strong spinulae, central area with some scattered spinulae. Dorsal surface of second labial palpomere without spinulae. Chaetotaxy. Antenna ( Fig. 29 ): seta AN8 present.

Description, instar II. As instar I except for the following features. Color: head capsule with some maculae present around frontal sulci and on dorsolateral surface of parietale. Body: for morphometric measurements and ratios see Table 2 . Head capsule: nasale with two anteroventral denticles. Chaetotaxy. Head capsule: with 17–18 secondary setae distributed in the area between FR1 and PA7, and near PA18. Outer gFR2 setae spiniform. Mandibles: with 2 short secondary setae at the base and 29–35 secondary minute sensilla distributed mainly along dorsolateral surface. Antenna: A1 with numerous secondary setae arranged as follows: 6–7 short setae on ventral surface, 2 slender setae and 14–15 stout spiniform setae on inner lateral surface, 6–7 setae on outer lateral surface, and two distal rings of long setae, apical one with 3 setae, the other with 7–8 setae. Maxilla: outer lateral surface of stipes with 2–4 hair-like secondary setae at the base, and 17–20 secondary setae unevenly distributed. Outer lateral surface of MP1 with 1 distal secondary seta. Labium: Mt with 1 stout secondary seta on each anterolateral angle, 4–6 secondary setae on laterobasal surfaces, 10–12 stout secondary setae on dorsal surface, and 4–6 thin secondary setae on ventral surface.

Description, instar III. As instar II except for the following features. Body: for morphometric measurements and ratios see Table 2 . Chaetotaxy. Head capsule: 18–19 secondary setae with similar distribution as in instar II. Mandibles: with 2 short secondary setae at the base and 29–40 secondary minute sensilla distributed mainly along dorsolateral surface. Antenna: A1 with numerous secondary setae arranged as follows: 4–7 short setae on ventral surface, 1–2 slender setae and 14–15 stout spiniform setae on inner lateral surface, 4–5 setae on outer lateral surface, and two distal rings of long setae, apical one with 3 setae, the other with 7–9 setae. Maxilla: outer lateral surface of stipes with 2–3 hair-like secondary setae at the base, and 14–18 secondary setae unevenly distributed. Labium: Mt with 1 stout secondary seta on each anterolateral angle, 6–9 secondary setae on laterobasal surfaces, 10–13 stout secondary setae on dorsal surface, and 6–10 thin secondary setae on ventral surface.

Description, pupa ( Figs. 20–21 ). Similar to the pupa of T. latus except for the following features. Body: TL (excluding pronotal styli and cerci) = 5.0– 5.8 mm; MW = 2.8–3.1 mm. Thorax: pronotum with 18–19 styli distributed as follows: 4 on pronotal disc and 14–15 on lateral surfaces (8 large styli anteriorly, 2 on each posterolateral angle, and 4–5 styli posteriorly). Metasternal spine short. Abdomen: segments II–VII with 6 styli (4 in a transverse row on each tergum and 1 about six times longer on each pleural area); segment IX with 2 short, apically unifid cerci; segments II–VI with lateral tubercles or horn-like projections.

Figures

FIGURES 1 – 6. Egg cases and larva of Tropisternus. 1, T. latus, egg case with mast; 2, T. latus, egg case without mast; 3, T. ovalis, egg case with larva emerging; 4, T. laevis, third instar larva, anterior aspect in dorsal view; 5, T. laevis, egg case showing the globular mast; 6, T. laevis, floating egg case as found in nature. Scale bars = 5 mm for figs. 1, 2, 5 and 6; 2 mm for fig. 3; 1 mm for fig. 4.

FIGURES 18 – 21. Tropisternus pupae. 18, T. latus, habitus, dorsal view; 19, T. latus, habitus, ventral view; 20, T. ovalis, habitus, dorsal view; 21, T. ovalis, habitus, ventral view. Scale bars = 1 mm.

FIGURES 22 – 28. Tropisternus ovalis, first instar larva. 22, Head capsule, dorsal view; 23, Head capsule, ventral view; 24, Frontoclypeus, dorsal view; 25, Labium, dorsal view; 26, Labium, ventral view; 27, Left mandible, dorsal view; 28, Right mandible, dorsal view. Scale bars = 0.1 mm.

FIGURES 29 – 31. Tropisternus ovalis, first instar larva. 29, Left antenna, dorsal view; 30, Left maxilla, dorsal view; 31, Right maxilla, ventral view. Scale bars = 0.1 mm.

Tables

TABLE 2. Measurements (in mm) and ratios for the three larval instars of Tropisternus ovalis.

Measure	Instar I	Instar II	Instar III
TL	3.30–3.50	4.00–7.50	10.50–12.00
MW	0.60–0.80	0.70–1.50	1.80–1.90
HL	0.46–0.47	0.60–0.72	0.85–0.89
HW	0.58–0.61	0.74	1.10–1.14
HL/HW	0.76–0.78	0.72–0.86	0.75–0.81
AL	0.50–0.51	0.71–0.73	0.84–0.91
A1L	0.28–0.29	0.46–0.47	0.57–0.61
A2L	0.12–0.13	0.14–0.15	0.14–0.16
A3L	0.10	0.11–0.12	0.13–0.14
A1L/(A2L+A3L)	1.22–1.26	1.77	2.07–2.15
HL/AL	0.90	0.83–0.86	0.93–1.06
HW/AL	1.16–1.19	1.16	1.25–1.31
SL	0.36–0.38	0.54–0.57	0.74–0.75
MPL	0.37	0.45–0.47	0.52–0.56
SL/MPL	0.96–1.00	1.21–1.22	1.32–1.45
MP1L	0.11	0.14–0.15	0.16–0.17
MP2L	0.03–0.04	0.04–0.05	0.06
MP2W	0.04	0.04	0.04–0.05
MP3L	0.11	0.14	0.16–0.18
MP4L	0.11–0.12	0.13	0.14–0.15
MP2L/MP2W	0.82–0.89	1.00–1.11	1.30–1.33
ML	0.73–0.75	0.99–1.01	1.27–1.31
LPL	0.11	0.13–0.14	0.15
LP1L	0.02	0.02–0.03	0.03–0.04
LP2L	0.08–0.09	0.10–0.11	0.11–0.12
LP2L/LP1L	3.40–3.60	3.67–4.20	2.75–4.00
LigL/LPL	0.54–0.57	0.46–0.58	0.63–0.67
MtW	0.17	0.25–0.26	0.36–0.38
PrmtW/PrmtL	0.99–1.00	0.85–0.88	0.72–0.75
PrmtW/MtW	0.52–0.54	0.40–0.45	0.32–0.36
LEG 1 L	1.19–1.27	1.72–1.75	2.38–2.44
LEG 2 L	1.25–1.34	1.77–1.89	2.53–2.57
LEG 3 L	1.43–1.44	1.95–2.00	2.85–2.90
LEG 3/LEG 1	1.13–1.20	1.13–1.14	1.17–1.22
LEG 3/LEG 2	1.07–1.15	1.06–1.10	1.11–1.14
LEG 1 (TITA/FE)	0.80–0.88	0.75–0.78	0.75–0.76
LEG 2 (TITA/FE)	0.79–0.81	0.69–0.73	0.68–0.70
LEG 3 (TITA/FE)	0.82–0.87	0.75–0.77	0.68–0.72
LEG 1 (CL/TITA)	0.63	0.54	0.45–0.48
LEG 2 (CL/TITA)	0.53–0.72	0.57–0.61	0.49–0.54
LEG 3 (CL/TITA)	0.63–0.64	0.49–0.55	0.51