Gonioctena gracilicornis

Gonioctena gracilicornis (Kraatz, 1879)

(Figs 7–12, 26, 34–37)

Gonioctena gracilicornis: Medvedev & Zaitsev 1980: 105 (key to larva, illustration of seta, tarsugulus).

Gonioctena (Gonioctena) gracilicornis: Medvedev & Zaitsev 1978: 119 (key to larva, illustration of mesonotum, tarsugulus); Medvedev 1982: 179 (key to larva, illustration of tarsugulus); Zaitsev & Medvedev 2009: 145 (key to larva, after Medvedev & Zaitsev 1978).

Last instar larva. Body length 10.6–11.7 mm, width 3.1–3.3 mm, head width 1.60–1.70 mm (n = 5). Body elongate, rather broad, widest at abdominal segments III–IV, thence moderately narrowed posteriorly and slightly convex dorsally (Fig. 7). General coloration of integument yellowish-white, but densely covered with strongly sclerotized platelets; tubercles dark brown, whereas ventral ones paler; head blackish-brown with anterior half of clypeus brown; legs dark brown to brown. Eversible glands present on anterior margin of abdominal segment VIII. Pseudopods absent.

Head. Hypognathous, rounded, strongly sclerotized (Fig. 8). Vertex with 4 pairs of minute setae; epicranium with 7 pairs of setae; temporal side of head with 3 pairs of setae. Epicranial suture distinct; frontal suture not reaching antennal socket; endocarina well developed. Frons slightly depressed medially, with 5 pairs of setae. Clypeus almost straight at anterior margin, with 3 pairs of setae. Labrum deeply emarginate with 2 pairs of setae and 1 pair of campaniform sensilla placed medially and 3 pairs of minute setae placed at anterior border (Fig. 10); epipharynx with 3 pairs of stout setae at anterior margin. Mandible palmate, 5-toothed, with 2 setae and 2 campaniform sensilla (Fig. 12). Maxillary palp 3-segmented; palpomere I transverse with 1 seta and 2 campaniform sensilla; II rectangular with 3 setae and 1 campaniform sensillum; III subconical with 1 seta, 1 digitiform sensillum and 1 campaniform sensillum on sides and a group of peg-like sensilla at the apex; palpifer distinct with 2 setae (Fig. 11). Mala rounded with 15 setae and 1 campaniform sensillum; stipes longer than wide with 3 setae; cardo with 1 seta. Labial palp 2-segmented; palpomere I rectangular with 1 campaniform sensillum; II subconical with 1 campaniform sensillum on outer margin and a group of peg-like sensilla at the apex. Hypopharyngeal area with 3 pairs of minute setae and 2 pairs of campaniform sensilla. Prementum with 1 pair of setae; postmentum widely covered with spinules, with 3 pairs of setae. Stemmata 6 on each side, 4 of them located above antenna and 2 behind antenna. Antenna short, 3-segmented; antenomere I transverse with 2 campaniform sensilla; II stout, more or less as wide as long, with a conical sensorium and 4 minute setae apically; III subconical with 6 minute setae apically.

Thorax. Prothorax with D-DL-EP (49–59L 3–5S) largest; P (2L 1S); ES-SS (4S) (Fig. 26). Meso- and metathorax with Dai (1L 1S); Dae (1L 1S); ad1 (1S) and ad2 (1S); DLai (2–3L 0–1S); Dpi (1L 2S); Dpe-DLpi (5–6L 1–2S) slightly larger than Dpi; DLe (8–10L 3S 1M) large and produced laterally; EPa (5–6L); EPp (3–4L); P (3–4S); SS (1S); ES (2–3S); sternal region with 3 additional setae arising from sclerotized bases. Mesothoracic spiracles annuliform; peritreme fused with EPa. Legs rather stout; tibia with 9 setae; tarsungulus large, strongly curved, basal tooth weakly developed, with 1 seta (Fig. 9).

Abdomen. Segments I–V with Dai (1L 1–2S) on both sides fused; Dae (1L 2S 1M); DLai (1L 2–4S); DLae (1S 2M) small; Dpi (1L 3S) on both sides fused; Dpe (1L 2S); DLp (3L 1M); EP (8–10L 0–1S) produced laterally; P (3–4L 2–3M); PS-SS (4–5S); ES (2–3S); as1 (1M) and as2 (1S). Segment VI with Dai and Dae, Dpi and Dpe fused respectively. Segments VII–VIII each with dorsal and dorso-lateral tubercles completely fused (8–9L 8–10S 2–4M and 6–8L 5S 12M respectively). Segment IX with dorsal to epipleural tubercles completely fused (10–11L 5–6S 2–3M). Segment X with pygopod well developed. Spiracles present on segments I–VIII.

Diagnosis. The last instar larva of Gonioctena gracilicornis is very similar to that of G. viminalis in the body shape, coloration, and tubercular pattern. However, this species can be distinguished by the tubercles covered with relatively long setae (relatively short in G. viminalis), tubercle Dpi on both sides of abdominal segments I–V completely fused (weakly fused in G. viminalis), and basal tooth of tarsungulus weakly developed (well developed in G. viminalis).

Material examined. 6 larvae, South Korea, Gyeongbuk Prov., Bonghwa-gun, Socheon-myeon, Buncheon-ri, 36°57'22.9"N, 129°04'30.3"E, 13.V.2006, H.W. Cho; 4 larvae, South Korea, Gangwon Prov., Pyeongchang-gun, Yongpyeong-myeon, Nodong-ri, Nodong Valley, 37°42'06.3"N, 128°28'53.9"E, 31.V.2006, H.W. Cho; 5 larvae, same data as preceding one except for 6. VI.2009; 5 larvae, South Korea, Gangwon Prov., Pyeongchang-gun, Daegwallyeong-myeon, Hoenggye-ri, 37°40'49.2"N, 128°44'58.1"E, 27.V.2018, H.W. Cho.

Distribution. Russia (East Siberia, Far East, Sakhalin), Mongolia, China (Heilongjiang), North Korea, South Korea.

Biological notes. Overwintered adults appear during mid-May (Fig. 37); they mate and lay 5– 11 eggs per cluster on the leaves of Salix koriyanagi. The eggs contain fully developed embryos and hatch after several hours (Fig. 34). The newly hatched larvae gregariously feed on young leaves (Fig. 35), but become solitary as they mature (Fig. 36). They raise the tip of the abdomen everting glands when disturbed. There are four larval instars, and pupation occurs in soil. The adults emerge during mid-June, and they feed and hibernate without mating. The larvae take 10–11 days to pupate, and then take 6–8 days to emerge as adults at room temperature.