Tropisternus (Pristoternus) laevis ( Sturm, 1826 )

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 : 392-395

Tropisternus (Pristoternus) laevis ( Sturm, 1826)

( Figs. 4–6 , 32–41 )

Material examined. Four egg cases, 2 larvae of instar I, 2 of instar II, 3 of instar III and 1 pupa were used for the descriptions. Egg cases were collected at the following locality: Argentina: Entre Ríos Province, El Palmar National Park, II-2004 (see Fig. 1 E in Torres et al. 2007).

Description, egg case ( Figs. 5–6 ). Whitish, of variable shape according to the substrate, mostly subtriangular in cross section. Mast present, distal part of mast made of loosen silk, appearing globular. Length = 5.0– 7.4 mm, width = 2.2–7.5 mm, height = 2.5–3.4 mm; cap length = 3.2–3.3 mm; mast length = 6.2–7.0 mm. Mast length/cap length = 1.89–2.19.

Description, instar I ( Figs. 32–41 ). Color: Head capsule testaceous to pale brown except for some brown areas posterior to nasale, around frontal sulci, and laterally in the parietale. Thoracic tergites testaceous to pale brown, with several brown maculae. Cephalic and thoracic appendages testaceous. Body: for morphometric measurements and ratios see Table 3 . Head capsule ( Figs. 32–34 ): nasale with 7 teeth on anterior margin, without anteroventral denticles ( Fig. 34 ). Mandibles ( Figs. 37–38 ): distal tooth of retinaculum bifid apically, outer lateral surface slightly serrate. Labium ( Figs. 35–36 ): anterolateral angles of mentum strongly projected forward. Dorsal surface of second labial palpomere without spinulae. Dorsal surface of mentum with strong spinulae, central area with very few scattered spinulae. Chaetotaxy. Antenna ( Fig. 39 ): seta AN8 present.

Description, instar II. As instar I except for the following features. Color: head capsule with brown color pattern around frontal sulci, parietale with lateral maculae. Body: for morphometric measurements and ratios see Table 3 . Chaetotaxy. Head capsule: with 13–16 secondary setae distributed in the area delimited by the intersection of PA7, PA8 and FR1, and between PA18-30. Outer gFR2 setae spiniform. Mandibles: with 2 short secondary setae at the base and 25–33 secondary minute sensilla distributed mainly along dorsal and lateral surfaces. Antenna: A1 with numerous secondary setae arranged as follows: 5–8 short setae on ventral surface, 1 slender seta and 13–15 stout spiniform setae on inner lateral surface, 4–5 setae on outer lateral surface, and two distal rings of long setae, apical one with 2–3 setae, the other with 7 setae. Maxilla: Outer lateral surface of stipes with 2 hair-like secondary setae at the base, and 25–33 secondary setae unevenly distributed. Labium: Mt with 1 stout secondary seta on each anterolateral angle, 2–3 secondary setae on laterobasal surfaces, 10–13 stout secondary setae on dorsal surface, and 3–4 thin secondary setae on ventral surface.

Description, instar III. As instar II except for the following features. Color: head capsule with well defined color pattern ( Fig. 4 ). Body: for morphometric measurements and ratios see Table 3 . Chaetotaxy. Head capsule: 13–19 secondary setae with similar distribution as in instar II. Mandibles: with 1–2 short secondary setae at the base and 20–23 secondary minute sensilla distributed mainly along dorsal and lateral surfaces. Antenna: A1 with numerous secondary setae arranged as follows: 5–6 short setae on ventral surface, 1–3 slender setae and 15–16 stout spiniform setae on inner lateral surface, 6–7 setae on outer lateral surface, and two distal rings of long setae, apical one with 2–3 setae, the other with 6–8 setae. Maxilla: Outer lateral surface of stipes with 1–3 hair-like secondary setae at the base, and 13–17 secondary setae unevenly distributed. Labium: Mt with 1 stout secondary seta on each anterolateral angle, 3–7 secondary setae on laterobasal surfaces, 13–17 stout secondary setae on dorsal surface, and 5–8 thin secondary setae on ventral surface.

Description, pupa. Similar to the pupa of T. latus except for the following features. Body: TL (excluding pronotal styli and cerci) = 7.9 mm; MW = 3.0 mm. Thorax: pronotum with 22 styli distributed as follows: 4 on pronotal disc and 18 on lateral surfaces (8 large styli anteriorly, 2 on each postero-lateral angle, and 6 posteriorly). Abdomen: segments II–VII with 6 styli (4 in a transverse row on each tergum and 1 about 40% longer on each pleural area).

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 32 – 38. Tropisternus laevis, first instar larva. 32, Head capsule, dorsal view; 33, Head capsule, ventral view; 34, Frontoclypeus, dorsal view; 35, Labium, dorsal view; 36, Labium, ventral view; 37, Left mandible, dorsal view; 38, Right mandible, dorsal view. Scale bars = 0.1 mm.

FIGURES 39 – 41. Tropisternus laevis, first instar larva. 39, Left antenna, dorsal view; 40, Left maxilla, dorsal view; 41, Right maxilla, ventral view. Scale bars = 0.1 mm.

Tables

TABLE 3. Measurements (in mm) and ratios for the three larval instars of Tropisternus laevis.

Measure	Instar I	Instar II	Instar III
TL	3.55–4.20	3.60–7.10	8.50–11.50
MW	0.75	0.90–1.25	2.10–2.30
HL	0.46–0.47	0.66–0.76	0.93–0.94
HW	0.53–0.56	0.90–1.01	1.09–1.25
HL/HW	0.82–0.85	0.74–0.75	0.74–0.86
AL	0.48–0.49	0.71–0.78	1.04–1.09
A1L	0.27–0.28	0.48–0.51	0.70–0.76
A2L	0.12	0.14–0.15	0.18–0.19
A3L	0.09	0.10–0.12	0.15
A1L/(A2L+A3L)	1.26–1.33	1.93–2.00	2.09–2.30
HL/AL	0.94–0.97	0.93–0.97	0.85–0.90
HW/AL	1.10–1.18	1.26–1.29	1.05–1.14
SL	0.33–0.38	0.52–0.61	0.78–0.89
MPL	0.31–0.32	0.40–0.41	0.49–0.52
SL/MPL	1.07–1.16	1.31–1.48	1.61–1.70
MP1L	0.10	0.14	0.19
MP2L	0.03	0.17–0.19	0.06–0.07
MP2W	0.05	0.05	0.05
MP3L	0.09–0.10	0.11–0.12	0.13–0.15
MP4L	0.09	0.11	0.10–0.13
MP2L/MP2W	0.58–0.74	0.85–0.95	1.20–1.27
ML	0.63–0.70	0.92–1.03	1.27–1.42
LPL	0.09–0.10	0.13	0.18
LP1L	0.02	0.02–0.03	0.04–0.05
LP2L	0.07–0.08	0.10	0.13–0.14
LP2L/LP1L	4.00–4.29	3.82–4.37	2.60–3.50
LigL/LPL	0.49–0.63	0.51–0.62	0.61–0.67
MtW	0.16–0.17	0.25	0.40–0.41
PrmtW/PrmtL	0.88–1.00	0.81–0.82	0.65–0.76
PrmtW/MtW	0.52–0.54	0.41–0.42	0.32–0.33
LEG 1 L	1.02–1.09	1.71–1.74	2.60–2.62
LEG 2 L	1.17–1.20	1.76–1.78	2.77
LEG 3 L	1.21–1.29	1.92–2.05	2.97–3.01
LEG 3/LEG 1	1.18	1.12–1.18	1.14–1.15
LEG 3/LEG 2	1.01–1.10	1.08–1.16	1.07–1.09
LEG 1 (TITA/FE)	0.90–0.93	0.80–0.81	0.77–0.78
LEG 2 (TITA/FE)	0.85–0.93	0.80	0.70–0.73
LEG 3 (TITA/FE)	0.91–0.94	0.80–0.81	0.76–0.77
LEG 1 (CL/TITA)	0.58–0.59	0.39–0.45	0.40–0.43
LEG 2 (CL/TITA)	0.61–0.64	0.46–0.55	0.43–0.47
LEG 3 (CL/TITA)	0.56–0.57	0.48–0.51	0.38–0.39