Gonioctena coreana (Bechyně, 1948)

Cho, Hee-Wook, 2019, Redescription of mature larva and biological notes on the nominotypical subgenus Gonioctena Chevrolat (Coleoptera: Chrysomelidae: Chrysomelinae) from South Korea, Zootaxa 4544 (4), pp. 557-571 : 558-559

Gonioctena coreana (Bechyně, 1948)

( Figs 1–6 , 25 , 30–33 )

Gonioctena (Gonioctena) coreana: Medvedev & Zaitsev 1978: 118 (key to larva, illustration of abdominal segment I); Zaitsev & Medvedev 2009: 145 (key to larva, after Medvedev & Zaitsev 1978).

Last instar larva. Body length 9.8–11.0 mm, width 3.1–3.3 mm, head width 1.80–1.90 mm (n = 5). Body elongate, rather broad, widest at abdominal segments III–IV, thence moderately narrowed posteriorly and slightly convex dorsally ( Fig. 1 ). General coloration of integument yellowish-white, but densely covered with strongly sclerotized platelets; dorsal tubercles dark brown, whereas ventral ones paler; head blackish-brown with anterior half of clypeus yellowish-brown; legs dark brown to brown. Eversible glands present on anterior margin of abdominal segment VIII. Pseudopods absent.

Head. Hypognathous, rounded, strongly sclerotized ( Fig. 2 ). Vertex with 4 pairs of minute setae; epicranium with 8 pairs of setae; temporal side of head with 2 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 2 pairs of minute setae placed at anterior border ( Fig. 4 ); epipharynx with 4 pairs of stout setae at anterior margin. Mandible palmate, 5-toothed, with 2 setae and 2 campaniform sensilla ( Fig. 6 ). 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. 5 ). 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 (47–54L 5–7S) largest; P (5–6S); ES-SS (5–6S) ( Fig. 25 ). Meso- and metathorax with Dai (1L 2S); Dae (1L 1–3S); ad1 (1M) and ad2 (1M); DLai (2–4S); Dpi (1L 3–4S); Dpe-DLpi (3–5L 2–7S) larger than Dpi; DLe (4–7L 6S 3M) large and produced laterally; EPa (4–6S); EPp (3–4L 1–3S); P (3–4S); SS (1S); ES (2–3S); sternal region with 4 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 well developed, with 1 seta ( Fig. 3 ).

Abdomen. Segments I–V with Dai (1L 2–3S) on both sides fused; Dae (1L 4S 1M); DLai (1L 3–4S); DLae (1S 2M) small, sometimes divided into 2 tubercles; Dpi (1L 3–4S); Dpe (1L 3–4S); DLp (3L 1–2S); EP (4–6L 3–5S) produced laterally; P (3L 2S 1M); PS-SS (4–5S); ES (2S); 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 (6–8L 10–13S 1M and 6–9L 7–13S 7–12M respectively). Segment IX with dorsal to epipleural tubercles completely fused (7L 11–12S 2M). Segment X with pygopod well developed. Spiracles present on segments I–VIII.

Diagnosis. The last instar larva of Gonioctena coreana is very similar to those of G. gracilicornis and G. viminalis in the body shape, coloration, and tubercular pattern. However, this species can be distinguished by the tubercle Dai on meso- and metathorax with 1 long and 2 short setae (1 long and 1 short setae in the other species), and Dpi on both sides of abdominal segments I–V completely separated (completely fused in G. gracilicornis and weakly fused in G. viminalis ).

Material examined. 16 larvae, South Korea, Gangwon Prov., Samcheok, Wondeok-eup , Nogok-ri , Gilgok Valley , 37°12'50.7"N, 129°19'04.1"E, 9.V.2005 , H.W. Cho; 11 larvae, South Korea, Gyeongbuk Prov., Yeongyanggun, Subi-myeon , Suha-ri , Suha Valley , 36°49'46.9"N, 129°16'08.8"E, 7.V.2005 , H.W. Cho; 21 larvae, same data as preceding one except for 30.IV.2006 .

Distribution. Mongolia, Russia (Far East), China (Jilin), North Korea, South Korea.

Biological notes. Overwintered adults appear during late April; they mate and lay eggs on the leaves of Salix gracilistyla . The females laid larvae that were enclosed within chorion ( Fig. 30 ), and they hatched after several hours; therefore, this species is ovoviviparous. The early instar larvae gregariously feed on young leaves ( Fig. 31 ), but become solitary as they mature ( Fig. 32 ). They raise the tip of the abdomen everting glands when threatened. There are four larval instars, and pupation occurs in soil. The adults emerge during late May ( Fig. 33 ); they feed and hibernate without mating. The larvae take 9–11 days to pupate, and then take 7–8 days to emerge as adults at room temperature.

Figures

FIGURES 1–6. Gonioctena coreana, last instar larva. 1. lateral habitus; 2. head; 3. tibia and tarsungulus; 4. labrum; 5. maxillae and labium; 6. mandible.

FIGURES 25–29. Schematic presentation of tubercular patterns (top: prothorax; middle: mesothorax; bottom: 2 nd abdominal segment), last instar larva. 25. Gonioctena coreana; 26. Gonioctena gracilicornis; 27. Gonioctena jacobsoni, dark type; 28. Gonioctena jacobsoni, light type; 29. Gonioctena viminalis.

FIGURES 30–33. Gonioctena coreana. 30. newly laid larvae; 31. early instar larvae; 32. mature larvae; 33. adult.