Description of the larvae of Platambus fimbriatus (Sharp, 1884)

Source of material. 1 instar I, 1 instar II, 10 instar III, Japan: Echi riv., Tanesato, Notogawa-cho, Shiga Pref., 22.II.2015; 20.XII.2015; 10.I.2016; R. Okada leg; 5 instar I, 1 instar II, Japan: Abukuma riv., Tsuruo, Saigo-mura, Fukushima Pref., 8.I.2017 R. Okada leg. Larvae were identified ex societate imaginis. Both Platambus fimbriatus and P. pictipennis occur at these two localities. Larvae of P. fimbriatus, however, could readily be recognized using features listed below.

Diagnosis. First instar larva of P. fimbriatus can be distinguished from the other species studied by the following combinations of features: frontoclypeus with less than 10 spatulate setae (Fig. 29); seta FR3 shorter than seta FR2 (Fig. 29); seta PA6 subequal in length to seta PA7 (Fig. 29); primary seta LA10 inserted subapically (Fig. 36); setae TI2, TI3, TI6, TI7, TA6, and TA7 bluntly pointed apically; seta UR4 not inserted contiguously to setae UR2 and UR3; ratio L3/HW <2.90. In addition to color patterns of head capsule (Fig. 59), last abdominal segment, and urogomphi (Figs 71, 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 29–42, 74). Color. Dorsal surface of head capsule predominantly dark brown; frontoclypeus yellowish anteriorly, dark brown around each egg burster; parietale dark brown, pal- er over occipital region; head appendages pale yellow, A3, A4, MP3, MP2, MP3 and LP2 infuscate apically; thoracic and abdominal terga I to VII pale brown; LAS predominantly dark brown; urogomphi pale yellow basally, dark brown over distal half; legs predominantly pale yellow, dark brown apically.

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

Head. Head capsule (Figs 29–30). Rounded, sides slightly diverging posteriorly; frontoclypeus with 10 spatulate setae. Antenna (Figs 31–32). A3’ finger-like.

Chaetotaxy. Seta FR3 shorter than seta FR2; seta PA6 subequal or longer than seta PA7; seta PA13 shorter than PA12; prementum with one additional seta on dorsal surface; setae TI2, TI3, TI6, TI7, TA6, and TA7 bluntly pointed apically; seta AB2 shorter than seta AB9; seta AB15 longer than seta AB11; seta UR4 not inserted contiguously to setae UR2 and UR3; position and number of additional setae on legs are shown in Table 1.

Instar II (Fig. 77). As first-instar larva except as follows:

Color. Dorsal surface of LAS yellowish anteriorly, dark brown over posterior half.

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

Head. Head capsule. Frontoclypeus with 20–21 spatulate setae. Antenna. A3’ bulge-like.

Chaetotaxy. Position and number of secondary setae on legs are shown in Table 1; parietale with 4 spine-like secondary setae on lateral margin of each side; anterodorsal secondary setae on TI and TA bluntly pointed apically.

Instar III (Figs 59, 65–66, 71, 80). As second-instar larva except as follows:

Color. Dorsal surface of head capsule yellowish; parietale yellowish with a narrow V-shaped dark brown marking across capsule at about mid-length and some brown maculae posteriorly; pro- and mesotergum and abdominal segments yellowish with several brown maculae, metanotum predominantly dark brown; LAS yellowish anteriorly, dark brown over distal 1/3 to 1/2; urogomphi predominantly yellow.

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

Head. Head capsule (Fig. 59). Frontoclypeus with 26–31 spatulate setae.

Chaetotaxy. Position and number of secondary setae on legs are shown in Table 1; parietale with 6–8 spine-like secondary setae along lateral margin.

Habitat. Larvae occur along quiet margins of moderate sized rivers flowing on sandy bottom. First-instar larvae are mainly collected along the banks under stones in shallow water. Whereas also collected in shallow parts, both second- and third- instar larvae appear to be more abundant in dry grass deposits (Fig. 85).