First instar larva. Body length 2.12–2.38 mm, width 0.56–0.62 mm, head width 0.42–0.44 mm (n = 3). Body yellowish-white with head brown, tubercles and legs light brown in alcohol; integument moderately covered with sclerotized platelets. Defensive glands very large on meso- and metathorax, but almost invisible on abdominal segments I–VII. Egg bursters present on meso- and metathorax. Head and mouthparts similar in the shape and chaetotaxy to those of the third instar larva.

Thorax. Prothorax with D-DL-EPa (2–3L 5–6S 2–3M) entirely pigmented; EPp (1S); P (1M); ES-SS (2M) weakly sclerotized (Fig. 15). Meso- and metathorax with Da (2S); Dp (1S); DLi (1S 2M) with a small egg burster situated anterior to a short seta; DLe (2L 2M) conical with a large defensive gland; EPa (1S); EPp (1S); P (1M); SS (1M) and ES (1M) weakly sclerotized.

Abdomen. Segments I–VI with Dai (1S); Dp (2S 1M); DL (1L 2S); EP (1L 1S 0–1M); P (1S 1M); PS-SS (3M) divided into two tubercles; ES (1M) on both sides generally fused. Segment VII with dorsal tubercles enlarged and fused. Segments VIII–IX each with dorsal and dorso-lateral tubercles enlarged and fused. Segment X with pygopod well developed.

Third (last) instar larva. Body length 4.60–5.80 mm, width 1.50–1.90 mm, head width 0.85–0.90 mm (n = 7). Body elongate, rather broad, widest at meso- and metathorax, thence moderately narrowed posteriorly (Fig. 1) and moderately convex dorsally (Fig. 2). General coloration of integument yellowish-white in alcohol; dorso-lateral region covered with dense platelets, forming a pair of longitudinal bands; head dark brown with anterior region and mouthparts largely yellowish-white; dorsal tubercles small, pale brown to dark brown, whereas ventral ones reduced (Fig. 3); legs pale yellow with apex of each segment brown. Defensive glands present on meso- and metathorax and abdominal segments I–VII.

Head. Hypognathous, rounded, strongly sclerotized (Fig. 6). Vertex with four pairs of minute setae; epicranium with six pairs of long setae; temporal side of head with three pairs of long setae. Epicranial suture distinct; frontal suture short, not reaching antennal socket; endocarina well developed. Frons with four pairs of long setae. Clypeus trapezoidal with two pairs of setae. Labrum slightly emarginate with two pairs of setae and two pairs of campaniform sensilla placed medially and one pair of setae placed at anterior border (Fig. 11); epipharynx with four pairs of stout and four pairs of small setae at anterior margin and one pair of small setae placed medially (Fig. 12). Mandible palmate, 4-toothed, with two setae and two campaniform sensilla (Figs 7–8). Maxillary palp 3-segmented; palpomere I transverse with one seta and one campaniform sensillum; II rectangular with two setae and one campaniform sensillum; III subconical with one seta, one digitiform sensillum and one campaniform sensillum on sides and a group of peg-like sensilla at the apex; palpifer distinct with two setae (Fig. 13). Mala rounded with eight pointed setae, two blunt setae and one campaniform sensillum; stipes longer than wide with three setae; cardo without setae. Labial palp 2-segmented; palpomere I rectangular with singe campaniform sensillum; II subconical with one campaniform sensillum below the apex and a group of peg-like sensilla at the apex. Hypopharyngeal area with three pairs of short setae and two pairs of campaniform sensilla. Prementum with two pairs of short setae and one pair of small setae – each of them placed at base of labial palp; postmentum with three pairs of setae. Stemmata six on each side, four of them located above antenna and two behind antenna. Antenna short, 3-segmented; antenomere I transverse with four campaniform sensilla; II stout, more or less as wide as long, with a conical sensorium and five small setae apically; III subconical with six small setae apically (Figs 9–10).

Thorax. Prothorax with D-DL-EPa (8–9L 2–3S) largest and pigmented only on dorso-lateral region; EPp (1S); P (1S) not sclerotized; ES-SS represented by a short seta (Fig. 16). Meso- and metathorax with Da (2S) small and transverse; Dp (1L) subequal to Da in size; DLi (1L 2S) larger than Da and Dp; DLe (2L 2–3S 1M) large and conical with a defensive gland; EPa (1L); EPp (1L); P (1S) not sclerotized; SS (1S) and ES (1S) represented by setae. Mesothoracic spiracles annuliform; peritreme fused with EPa. Legs rather stout; tibia with nine setae; tarsungulus large, strongly curved, basal tooth not developed, with 1 short seta (Fig. 14).

Abdomen. Segments I–VI with Dai (1S) very small; Dp (2L 1S) small, but larger than Dai; DL (2L 1M) conical with a defensive gland; EP (2L) and P (2S) not sclerotized; PS-SS (3S) and ES (1S) represented by setae. Segment VII with dorsal tubercles enlarged and fused; DL with a defensive gland. Segments VIII–IX each with dorsal and dorso-lateral tubercles fused. Segment X with pygopod well developed. Spiracles present on segments I–VIII.

Figures 1–3. 

Habitus of Phratora koreana, third instar larva. 1 dorsal 2 lateral 3 ventral.

Figures 4–5. 

Phratora koreana, live larva. 4 first and second instar larvae 5 third instar larva.

Figures 6–14. 

Phratora koreana, third instar larva. 6 head 7–8 mandibles 9–10 antennae 11 labrum 12 epipharynx 13 maxillae and labium 14 tibia and tarsungulus.

Figures 15–16. 

Schematic presentation of tubercular patterns (top: prothorax, middle: mesothorax, bottom: abdominal segment II), Phratora koreana. 15 first instar larva 16 third instar larva.

The larva of Phratora koreana is easily distinguished from all other known species of Phratora by the presence of small tubercles Dai and Dp on abdominal segments I–VI. In other species of Phratora, Dai and Dp are present only on abdominal segment I and a large tubercle D is present on II–VI. The larva of Prasocuris glabra (Herbst) is also similar to that of Phratora koreana in the presence of tubercles Dai and Dp on abdominal segments I–VI, but tubercles of P. glabra are much larger (Hennig 1938).

South Korea: Gangwon, Gyeongnam, Jeju; Japan: Honshu (Takizawa 1985, 1990).

Overwintered adults appear in late May, mate and lay 8–15 yellowish eggs per cluster on leaves of Salix caprea in early June. The larvae gregariously feed on leaves until the final instar. There are three larval instars and pupation takes place in the soil. Newly emerged adults appear in early July.

Morphological changes in the pigmentation, tubercular pattern and defensive glands occur during the larval development. The first instar larva has well developed and pigmented tubercles, but after molting to the second instar larva, ventral tubercles are reduced and median region of D-DL-EPa is unpigmented (Fig. 4). The defensive glands on abdominal segments I–VII are well developed in the second and third instar larvae, whereas they are almost invisible in the first instar larva. A pair of longitudinal bands on account of very dense and strongly sclerotized platelets appear only in the third instar larva (Fig. 5).