Platambus pictipennis ( Sharp, 1873 )

Okada, Ryohei, Alarie, Yves & Michat, Mariano C., 2019, Description of the larvae of four Japanese Platambus Thomson, 1859 (Coleoptera: Dytiscidae: Agabinae) with phylogenetic considerations, Zootaxa 4646 (3), pp. 401-433 : 406-413

Description of the larvae of Platambus pictipennis ( Sharp, 1873)

Source of material. 10 instar I, 10 instar II, 10 instar III, Japan: Echi riv., Tanesato, Notogawa-cho, Shiga Pref, 22.II.2015; 7.III.2015; 20.XII.2015; 6–10.I.2016; 6.II.2016; R. Okada leg; 3 instar I, Japan: Abukuma riv., Tsuruo, Saigo-mura , Fukushima Pref., 8.I.2017, R. Okada leg ; 1 instar I, Japan: Shimokubo-dam, Fujioka-shi , Gunma Pref., 7.I.2016, N. Shimura leg. Larvae were reared ex ovo from adults collected at these localities

Diagnosis. First instar larva of P. pictipennis can be distinguished from the other species studied by the following combinations of features: frontoclypeus with less than 12 spatulate setae ( Fig. 1 ); A3’ short bulge-like ( Fig. 4 ); seta FR3 shorter than seta FR2 ( Fig. 1 ); seta PA6 longer than seta PA7 ( Fig. 1 ); primary seta LA10 inserted subapically ( Fig. 8 ); ratio L3/HW = 2.90–3.20. In addition to color patterns of head capsule ( Fig. 57 ), last abdominal segment, and urogomphi ( Figs 69 , 73–82 ), the total number of spatulate setae on frontoclypeus, secondary setae on pro- and mesofemur, and the presence/absence of ventral setae on protarsus ( Table 2 ) are helpful at discriminating later instars.

Instar I ( Figs 1–14 , 73 ). Color. Dorsal surface of head capsule predominantly dark brown; frontoclypeus creamy white distally, dark brown around each egg burster; parietale dark brown to black with a paired pale macula distal margin of ecdysial suture; head appendages pale yellow, A3, A4, MP3, and LP2 infuscate apically; thoracic and abdominal terga I to VII brown; LAS dark brown over 1/3 to 1/2 of anterior region, yellowish posteriorly; urogomphi pale yellow, basal region of median and distal group of sensilla dark brown; legs pale yellow.

Body. Measurements and ratios that characterize the body shape are shown in Table 3 .

Head. Head capsule ( Figs 1–2 ). Rounded, sides subparallel; frontoclypeus with 10–11 spatulate setae. Antenna ( Figs 3–4 ). A3’ bulge-like.

Chaetotaxy. Seta FR3 shorter than seta FR2; seta PA6 shorter than seta PA7; seta PA13 subequal or longer than seta PA12; prementum with one additional seta; setae TI2, TI3, TI6, TI7, TA6, and TA7 acute apically; seta AB2 shorter than seta AB9; seta AB15 subequal or slightly shorter than seta AB11; setae UR2, UR3 and UR4 inserted contiguously; position and number of additional setae on legs are shown in Table 1 .

Instar II ( Fig. 76 ). As first-instar larva except as follows:

Color. Dorsal surface of head capsule predominantly yellowish with W-shaped dark brown macula at about middle; thoracic and abdominal segments yellowish with several brown maculae.

Body. Measurements and ratios that characterize the body shape are shown in Table 3 .

Head. Head capsule. Frontoclypeus with 20–22 spatulate setae.

Chaetotaxy. Parietale with 5–8 spine-like secondary setae on the lateral margin; position and number of secondary setae on legs are shown in Table 2 ; anterodorsal secondary setae on TI and TA acute apically.

Instar III ( Figs 57 , 61–62 , 69 , 79 ). As second-instar larva except as follows:

Color. Thoracic and abdominal segments predominantly brown with several yellowish maculae.

Body. Measurements and ratios that characterize the body shape are shown in Table 3 .

Head. Head capsule ( Fig. 57 ). Frontoclypeus with 35–42 spatulate setae.

Chaetotaxy. Parietale with 6–8 spine-like secondary setae along lateral margin; position and number of secondary setae on legs are shown in Table 2 .

Habitat. Larvae were collected along the quiet margin of moderate size rivers ( Figs 83–85 ). First-instar larvae were generally collected in shallower areas, among roots of small grass whilst second- and third- instar larvae were mainly found along banks with withered grass hanging ( Fig. 83 ).

Figures

FIGURES 1–2. Platambus pictipennis (Sharp, 1873), instar I, head capsule: (1) dorsal aspect (colour pattern not represented); (2) ventral aspect. EB, egg bursters; TP, tentorial pits. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bar = 0.10 mm.

FIGURES 3–9. Platambus pictipennis (Sharp, 1873), instar I, head appendages: (3–4) antenna, (3) dorsal aspect; (4) ventral aspect; (5–6) maxilla, (5) dorsal aspect; (6) ventral aspect; (7–8) labium; (7) dorsal aspect; (8) ventral aspect; (9) mandible, dorsal aspect. Numbers and lowercase letters refer to primary setae and pores, respectively; filled squares refer to additional setae. Scale bars = 0.10 mm.

FIGURES 57–60. Head capsule of selected species of Platambus Thomson, 1859, instar III, dorsal aspect: (57) P. pictipennis (Sharp, 1873); (58) P. convexus Okada, 2011; (59) P. fimbriatus (Sharp, 1884); (60) P. sawadai (Kamiya, 1932). Scale bar = 0.50 mm.

FIGURES 69–72. Last abdominal segment and urogomphi of selected species of Platambus Thomson, 1859, instar III, dorsal aspect: (69) P. pictipennis (Sharp, 1873); (70) P. convexus Okada, 2011; (71) P. fimbriatus (Sharp, 1884); (72) P. sawadai (Kamiya, 1932). Scale bar = 0.50 mm.

FIGURES 73–82. Dorsal habitus of selected species of Platambus Thomson, 1859: (73– 75) instar I; (76–78) instar II; (79-82) instar III; (73, 76, 79) P. pictipennis (Sharp, 1873); (74, 77, 80) P. fimbriatus (Sharp, 1884); (75, 78, 81) P. sawadai (Kamiya, 1932); (82) P. convexus Okada, 2011. Scale bar = 1.00 mm in (73–78), 2.00 mm in (79–82).

FIGURES 61–68. Prothoracic leg of selected species of Platambus Thomson, 1859, instar III: (61–62) P. pictipennis (Sharp, 1873), (61) anterior aspect; (62) posterior aspect; (63–64) P. convexus Okada, 2011, (63) anterior aspect; (64) posterior aspect; (65–66) P. fimbriatus (Sharp, 1884), (65) anterior aspect; (66) posterior aspect; (67–68) P. sawadai (Kamiya, 1932), (67) anterior aspect; (68) posterior aspect. Scale bar = 0.50 mm.

FIGURES 83–88. Collecting localities of the larvae of Platambus Thomson, 1859: (83–85) Echi river, Shiga Prefecture, Western Japan, (83) moderate sized river, with withered grass hanging; (84) river bank with gravel bed; (85) shallow area with dry grass deposited; (86) Nishinopporo-sawa river, Hokkaido Prefecture, Northern Japan, small stream flowing under broadleaved trees; (87–88) Happudani river, Shiga Prefecture, Western Japan, (87) mountain stream; (88) gutters with constantly flowing clear water.