Tropisternus (Pristoternus) latus ( Brullé, 1837 ), Brulle, 1837

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 : 382-388

Tropisternus (Pristoternus) latus ( Brullé, 1837)

( Figs. 1–2 , 7–19 )

Material examined. Seven egg cases, 8 larvae of instar I, 6 of instar II, 5 of instar III and 5 pupae were used for the descriptions. Breeding adults were collected at the following locality: Argentina: Buenos Aires Province, Sierra de la Ventana (Ernesto Tornquist Provincial Park), X-2007 (see Fig. 1 in Fernández et al. 2010).

Description, egg case ( Figs. 1–2 ). Whitish, saccular, subtriangular in cross-section. Mast present (n = 4) ( Fig. 1 ) or absent (n = 3) ( Fig. 2 ). Length = 10.7–12.4 mm, width = 8.3–8.7 mm, height = 5.3–5.8 mm; cap length = 5.2–5.7 mm; mast length= 11.5–12.8 mm. Mast length/cap length = 2.21–2.24.

Description, instar I ( Figs. 7–17 ). Color: head capsule testaceous, with pale brown areas around frontal sulci and on dorsolateral surface of parietale. Cephalic and thoracic appendages yellowish. Thoracic tergites testaceous, with some pale brown scattered maculae; thoracic sternites testaceous. Body: for morphometric measurements and ratios see Table 1 . Head capsule ( Figs. 7–9, 12 ): nasale with 7 teeth on anterior margin, without anteroventral denticles ( Fig. 12 ). Mandibles ( Figs. 16–17 ): distal tooth of retinaculum bifid apically, outer lateral surface slightly serrate. Labium ( Figs. 10–11 ): anterolateral angles of mentum strongly projected forward. Dorsolateral surface of mentum with strong spinulae. Dorsal surface of second labial palpomere with some spinulae. Chaetotaxy. Antenna ( Fig. 13 ): seta AN8 present.

Description, instar II. As instar I except for the following features. Color: head capsule testaceous with brown areas around frontal sulci, maculae of parietale more notorious. Thoracic tergites with dark brown maculae. Body: for morphometric measurements and ratios see Table 1 . Head capsule: nasale with two anteroventral denticles. Chaetotaxy. Head capsule: with 68–84 secondary setae distributed in the area delimited by the intersection of PA6, PA7 and FR1, between PA7 and PA10, between PA21 and PA26, and in the stemmatal area. Outer gFR2 setae blunt or pointed. Mandibles: with 2 short secondary setae at the base and 18–21 secondary minute sensilla distributed mainly along dorsolateral surface. Antenna: A1 with numerous secondary setae arranged as follows: 12–14 short setae on ventral surface, 19–32 stout spiniform setae on inner lateral surface, 3–4 setae on outer lateral surface, and two distal rings of long setae, apical one with 4–5 setae, the other with 10–11 setae. Maxilla: outer lateral surface of stipes with 7–8 hair-like secondary setae at the base, and 32–36 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, 18–21 stout secondary setae on dorsal surface,and 8–11 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 1 . Chaetotaxy. Head capsule: 78–99 secondary setae with similar distribution as in instar II. Mandibles: with 2 short secondary setae at the base and 48–57 secondary minute sensilla distributed mainly along dorsolateral surface. Antenna: A1 with numerous secondary setae arranged as follows: 15–20 short setae on ventral surface, 33–36 stout spiniform setae on inner lateral surface, 6–7 setae on outer lateral surface, and two distal rings of long setae, apical one with 5 setae, the other with 9–12 setae. Maxilla: outer lateral surface of stipes with 5–6 hair-like secondary setae at the base, and 35–37 secondary setae unevenly distributed. Labium: Mt with 1 stout secondary seta on each anterolateral angle, 5–8 secondary setae on laterobasal surfaces, 21–23 stout secondary setae on dorsal surface, and 15–20 thin secondary setae on ventral surface.

Description, pupa ( Figs. 18–19 ). Color: Whitish (young pupae) to pale brown (mature pupae). Body: TL (excluding pronotal styli and cerci) = 11.3–12.6 mm; MW = 4.9–5.8 mm. Head: posterior surface with two oval sclerites close to midline, without supraorbital styli. Antennae partially hidden by pronotum. Maxillary palpi extending beyond base of mesocoxae. Thorax: pronotum with 22 styli distributed as follows: 2 on pronotal disc and 20 on lateral surfaces (10 large styli anteriorly, 2 on each postero-lateral angle, and 6 styli posteriorly). Meso- and metanotum with 2 styli close to midline. Metasternal spine long. Metathoracic legs partially covered by wingpads. Tibiae with two apical spines. Abdomen: segment I with 4 styli; segments II–VI with 8 styli (6 in a transverse row on each tergum and 1 about two thirds shorter on each pleural area); segment VII with 6 styli (4 tergal and 1 on each pleural area); segment VIII with a pair of minute styli posteriorly; all styli with irregular surface and bearing a terminal seta; segment IX with 2 long bifid cerci, each bearing 2 spines at mid-length; segments II–VI without 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 7 – 12. Tropisternus latus, first instar larva. 7, Head capsule, dorsal view; 8, Head capsule, ventral view; 9, Head capsule, right lateral view; 10, Labium, dorsal view; 11, Labium, ventral view; 12, Frontoclypeus, dorsal view. Scale bars = 0.1 mm.

FIGURES 13 – 17. Tropisternus latus, first instar larva. 13, Left antenna, dorsal view; 14, Left maxilla, dorsal view; 15, Right maxilla, ventral view; 16, Left mandible, dorsal view; 17, Right mandible, dorsal view. Scale bars = 0.1 mm.

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.

Tables

TABLE 1. Measurements (in mm) and ratios for the three larval instars of Tropisternus latus.

Measure	Instar I	Instar II	Instar III
TL	2.58–4.30	9.00–11.50	15.00–16.50
MW	0.83–1.00	2.00–2.50	3.50–4.00
HL	0.72–0.73	1.20–1.25	1.70–1.73
HW	0.96–0.99	1.55–1.73	2.23–2.25
HL/HW	0.74–0.75	0.72–0.77	0.76–0.77
AL	0.74–0.76	1.25–1.28	1.62–1.71
A1L	0.42–0.44	0.80–0.82	1.10–1.20
A2L	0.18	0.24	0.28
A3L	0.15	0.21–0.22	0.24
A1L/(A2L+A3L)	1.27–1.33	1.80	2.10–2.33
HL/AL	0.96–0.97	0.96–0.98	0.99–1.06
HW/AL	1.29–1.30	1.24–1.35	1.30–1.38
SL	0.54–0.55	0.97–0.99	1.38–1.40
MPL	0.46–0.47	0.67	0.83–0.85
SL/MPL	1.18	1.44–1.47	1.61–1.68
MP1L	0.14	0.24	0.29–0.31
MP2L	0.05	0.08–0.09	0.12–0.13
MP2W	0.06	0.08–0.09	0.08–0.09
MP3L	0.16	0.20	0.26
MP4L	0.11–0.12	0.15	0.16
MP2L/MP2W	0.85–0.92	0.94–1.13	1.39–1.53
ML	1.00–1.02	1.64–1.66	2.23
LPL	0.18–0.19	0.26–0.27	0.25–0.30
LP1L	0.04	0.05–0.06	0.05–0.07
LP2L	0.14–0.15	0.21	0.20–0.23
LP2L/LP1L	3.33–3.50	3.50–3.82	3.29–4.00
LigL/LPL	0.41–0.44	0.41–0.42	0.45–0.52
MtW	0.25	0.47–0.48	0.68–0.69
PrmtW/PrmtL	0.93–1.00	0.86–0.90	0.74–0.78
PrmtW/MtW	0.52	0.40	0.33–0.34
LEG 1 L	1.84–1.89	2.71–2.72	3.76–3.81
LEG 2 L	1.94–1.98	2.87–2.89	4.00–4.08
LEG 3 L	1.99–2.03	3.10–3.13	4.39–4.41
LEG 3/LEG 1	1.05–1.10	1.14–1.15	1.16–1.17
LEG 3/LEG 2	1.01–1.05	1.08	1.08–1.10
LEG 1 (TITA/FE)	0.74–0.80	0.74–0.77	0.72–0.73
LEG 2 (TITA/FE)	0.78–0.80	0.73	0.67–0.71
LEG 3 (TITA/FE)	0.81–0.89	0.78–0.79	0.73–0.76
LEG 1 (CL/TITA)	0.65	0.50–0.51	0.43–0.46
LEG 2 (CL/TITA)	0.64	0.50	0.44–0.47
LEG 3 (CL/TITA)	0.56–0.64	0.45–0.48	0.38–0.41