Tropisternus scutellaris Castelnau

Torres, Patricia L. M., Michat, Mariano C. & Archangelsky, Miguel, 2008, Description of the preimaginal stages of three species of the genus Tropisternus Solier, subgenus Strepitornus Hansen (Coleoptera: Hydrophilidae), with emphasis on morphometry and chaetotaxy, Zootaxa 1702, pp. 1-25 : 9-14

Tropisternus scutellaris Castelnau

( Figs. 1 , 4–19 , 22–29 )

Material examined. ARGENTINA: Buenos Aires Province: Bragado, breeding adults collected on 18.I.2002 by P. L. M. Torres (2 egg cases, 8 instar I, 4 instar II and 11 instar III larvae, 4 pupae, 3 emerged adults).

Egg case. Length = 4.00–7.00 mm, width = 4.00– 5.50 mm, height = 4.00–5.00 mm ( Fig. 1 ); cap length = 3.00– 3.80 mm; mast length = 6.50 mm. MastL/capL = 1.71–2.16.

First-instar larva. Morphometric measures detailed in Table 1; chaetotaxy of legs summarized in Table 2.

Second-instar larva. Morphometric measures detailed in Table 1.

Antenna. A1 with 7–8 short secondary setae on ventral surface; 13–16 stout secondary setae on inner margin, 3–4 short thin secondary setae on outer margin and dorsal surface; apical upper ring with 4 secondary setae, lower one with 9–10 secondary setae.

Maxilla. Outer margin of stipes with 2–3 stout secondary setae basally and 4–8 thin secondary setae unevenly distributed.

Labium. Mt with 1 stout secondary seta on each anterolateral edge, 2–6 secondary setae on laterobasal edge, 15–22 stout secondary setae on dorsal surface, and 2 secondary setae on ventral surface.

Legs. Chaetotaxy summarized in Table 2.

Third-instar larva. Morphometric measures detailed in Table 1.

Antenna. A1 with 7–10 short secondary setae on ventral surface, 11–15 stout secondary setae on inner margin, 5–6 short thin secondary setae on outer margin and dorsal surface; apical upper ring with 4 secondary setae, lower one with 9–10 secondary setae.

Maxilla. Outer margin of stipes with 2–4 stout secondary setae basally and 5–7 thin secondary setae unevenly distributed.

Labium. Mt with 1 stout secondary seta on each anterolateral edge, 6–8 secondary setae on laterobasal edges, 17–22 stout secondary setae on dorsal surface, and 2–5 secondary setae on ventral surface.

Legs. Chaetotaxy summarized in Table 2.

Pupa. TL (excluding pronotal styli and cerci) = 8.00–10.00 mm; MW = 4.50–5.20 mm. Pronotum with 22 styli distributed as follows: 2 on pronotal disc and 20 on margins (10 large styli on anterior margin, 2 on each posterolateral angle, and 6 along posterior margin).

Figures

FIGURES 1 – 3. Egg cases of Tropisternus: 1, T. scutellaris; 2, T. collaris; 3, T. parananus. Scale bar = 2.0 mm.

FIGURES 4 – 6. Tropisternus scutellaris, first-instar larva: 4, head capsule, dorsal view; 5, head capsule, ventral view; 6, frontoclypeus, dorsal view. Scale bars: Figs. 4 – 5 = 0.2 mm, Fig. 6 = 0.1 mm.

FIGURES 7 – 13. Tropisternus scutellaris, first-instar larva: 7, left mandible, dorsal view; 8, right mandible, dorsal view; 9, left maxilla, dorsal view; 10, right maxilla, ventral view; 11, left antenna, dorsal view; 12, labium, dorsal view; 13, labium, ventral view. Scale bars = 0.1 mm.

FIGURES 14 – 18. Tropisternus scutellaris, legs: 14, prothoracic leg of first-instar larva, anterior view; 15, detail of the same; 16, prothoracic leg of first-instar larva, posterior view; 17, prothoracic leg of third-instar larva, anterior view; 18, prothoracic leg of third-instar larva, posterior view. Scale bars = 0.1 mm.

FIGURES 19 – 21. Head capsule of third-instar larvae of Tropisternus, dorsal view: 19, T. scutellaris; 20, T. collaris; 21, T. parananus. Scale bar = 0.5 mm.

FIGURES 22 – 27. Tropisternus scutellaris, third-instar larva: 22, habitus, dorsal view; 23, left mandible, dorsal view; 24, right mandible, dorsal view; 25, labium, dorsal view; 26, left maxilla, dorsal view; 27, left antenna, dorsal view. Scale bars: Fig. 22 = 1.0 mm, Figs. 23 – 24 = 0.5 mm, Figs. 25 – 27 = 0.1 mm.

FIGURES 28 – 29. Tropisternus scutellaris, pupa: 28, dorsal view; 29, ventral view. Scale bar = 1.0 mm.