Plagiosterna adamsii ( Baly, 1864 )

Cho, Hee-Wook & Świętojańska, Jolanta, 2017, Larval morphology of Plagiosterna adamsii (Baly) and P. aenea (Linnaeus) with resurrection of Gastrolinoides Chûjô & Kimoto and P. formosana (Bates) (Coleoptera: Chrysomelidae: Chrysomelinae), Zootaxa 4236 (2), pp. 381-391 : 382-384

Description of the larva of Plagiosterna adamsii ( Baly, 1864)

( Figs 1–3 , 7–14 , 23 , 25, 26 )

First instar larva. Body length 2.10–2.30 mm, width 0.65–0.70 mm, head width 0.58 mm (n = 2). Body yellowish-white with head dark brown, tubercles and legs brown. Sclerotized platelets on dorsum rather dense, on venter sparse. Defensive glands present on meso- and metathorax and abdominal segments I–VII. Small egg bursters present on meso- and metathorax. Head and mouthparts similar in the shape and chaetotaxy to those of the last instar larva.

Thorax. Prothorax with D-DL-EPa (10L 7–11S 4–5M); EPp (1S 2M); P (3S); ES-SS (1S 2M) ( Fig. 25 ). Meso- and metathorax with Da (2S 3M) sometimes divided into large Dai and small Dae; Dp (1L 1S) smaller than Da; DLi (1L 1S 1–2M) with a very small egg burster situated anterior to a long seta; DLe (1L 4–5S 2M) conical with a defensive gland; EPa (4–5S); EPp (1L 4S); P (2–3S); SS (1M); ES (1S 1M).

Abdomen. Segments I–VI with D (1L 5–6S); DL (1L 3–4S) with a defensive gland; EP (1L 5–6S); P (1L 3S); PS-SS (2S 1–2M) generally divided into 2 tubercles; ES (2S) on both sides fused or separated; as1 (1M). Segment VII with D on both sides fused; DL with a defensive gland. Segment VIII with dorsal and dorsolateral tubercles fused. Segment IX with D-DL-EP (3S 5–7M) fused. Segment X with pygopod well developed.

Third (last) instar larva. Body length 10.3–11.4 mm, width 3.2–3.3 mm, head width 1.17–1.25 mm (n = 5). Body elongate, widest at abdominal segments II–III and moderately convex dorsally ( Figs 1–2 ). Head blackishbrown with mouthparts partially yellowish-white; dorsal tubercles brown to blackish-brown, whereas ventral ones much paler ( Fig. 3 ); dorsal integument brown except median line of thorax on account of very dense and strongly sclerotized platelets, whereas ventral one yellowish-white on account of sparse and weakly sclerotized platelets; legs brown with apex of each segment dark brown. Defensive glands present on meso- and metathorax and abdominal segments I–VII.

Head. Hypognathous, rounded, strongly sclerotized ( Fig. 7 ). Vertex with 4 pairs of minute setae; epicranium with 9 pairs of setae; temporal side of head with 4 pairs of setae. Epicranial suture distinct; frontal suture short, not reaching antennal socket; endocarina well developed. Frons with 4–5 pairs of setae. Clypeus trapezoidal with 3 pairs of setae. Labrum deeply emarginate with 2 pairs of short and 1 pair of minute setae and 2 pairs of campaniform sensilla placed medially and 1 pair of minute setae placed at anterior border ( Fig. 12 ); epipharynx with 3 pairs of stout setae at anterior margin ( Fig. 13 ). Mandible palmate, 5-toothed, with 2 setae and 2 campaniform sensilla ( Figs 8–9 ). Maxillary palp 3-segmented; palpomere I transverse with 1 seta and 1 campaniform sensillum; II rectangular with 2 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. 14 ). Mala rounded with 10 setae and 1 campaniform sensillum; stipes longer than wide with 3 setae; cardo without setae. Labial palp 2-segmented; palpomere I rectangular with 1 minute seta and 1 campaniform sensillum; II subconical with 1 campaniform sensillum on outer side and a group of peg-like sensilla at the apex. Hypopharyngeal area with 3 pairs of setae (2 of them placed internally, not visible on Fig. 14 ) and 1 pair of campaniform sensilla. Prementum with 2 pairs of setae; postmentum with spinules on basolateral region, 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 with a conical sensorium and 6 setae; III subconical with 5 setae and 1 campaniform sensillum ( Figs 10–11 ).

Thorax. Prothorax with D-DL-EPa (1L 21–26S) largest; EPp (2–3S) small and rounded; P (2S); ES-SS (3–5S) slightly sclerotized ( Fig. 26 ). Meso- and metathorax with Da (4–5S 1M) generally divided into large Dai and small Dae; Dp (2S) smaller than Da; DLi (3–4S) much smaller than Dp; DLe (1L 7–8S 1M) large and conical with a defensive gland; EPa (3–5S); EPp (1L 2–4S); P (2S); SS (1S) and ES (2–3S) slightly sclerotized. Mesothoracic spiracles annuliform; peritreme fused with EPa. Legs rather stout; tibia with 13 setae; tarsungulus strongly curved, basal tooth well developed, with 1 short seta ( Fig. 23 ).

Abdomen. Segments I–VI with D (6–8S) wider than long; DL (1L 3–4S) conical with a defensive gland; EP (1L 4–6S); P (1L 2–4S) smaller than EP; PS-SS (2–3S) sometimes divided into 2–3 tubercles, slightly sclerotized; ES (2S) on both sides fused or separated, slightly sclerotized; as1 (1S) very small. Segment VII with D on both sides fused; DL with a defensive gland. Segments VIII–IX each with dorsal and dorsolateral tubercles fused (2L 6– 7S 2M and 7–8S 2–4M respectively). Segment X with pygopod well developed. Spiracles present on segments I– VIII.

Diagnosis. The last instar larva of Plagiosterna adamsii is similar to that of P. formosana in the dark dorsum on account of strongly sclerotized platelets. However, this species can be distinguished from P. formosana by the pronotum entirely pigmented except a narrow median line, abdomen almost completely covered with sclerotized platelets and legs largely brown (median region of pronotum unpigmented, a pair of broad bands on metathorax and abdominal segments I–IV and legs largely yellowish-white in P. formosana ).

Material examined. 5 last instar larvae, South Korea, Gyeongbuk Prov., Andong, Songcheon-dong, 6.V.2006, H.Y. Kwon; 4 first and 5 last instar larvae, same data as preceding one except for 31.V.2009, H.W. Cho.

Distribution. China (Guandong, Guizhou, Liaoning, Sichuan, Yunnan, Zhejiang), Nepal, Korea ( Kippenberg 2010). The record from Japan is an error.

Host plant. Betulaceae : Alnus spp.

Biological notes. Plagiosterna adamsii is univoltine. Overwintered adults appear in early May, mate and lay clusters of eggs on leaves of Alnus in mid-May. Newly hatched larvae gregariously feed on young leaves, but later become solitary as they mature. Larvae molt two times to become fully grown. Pupation takes place on the leaf surface. Newly emerged adults are found from June to August. Plagiosterna aenea has a similar life cycle in South Korea.

Remarks. Baly (1864) described Lina adamsii from Chusan in China, however the original name and year of publication were wrongly cited as Melasoma adamsi Baly, 1884 by several authors (Gressitt & Kimoto 1963; Kippenberg 2010; Yang et al. 2014, etc.). Park et al. (2015) described immature stages of P. adamsii (as P. adamsi ) with several misinterpretations: illustrations of P. adamsii and P. aenea seem to be switched; mala (fused galea and lacinia) is misinterpreted as galea; misinterpreted number of mandibular setae; insufficient diagnostic characters at the species level. In the present publication the first instar larva of P. adamsii is shown to be highly similar to the last instar larva in the body shape, chaetotaxy of head and mouthparts, and tubercular pattern, however, it differs in the dorsal integument with less dense platelets and pronotal tubercle D-DL-EPa with relatively long setae.

Figures

FIGURES 1 – 3. Habitus of Plagiosterna adamsii, last instar larva. 1. dorsal view; 2. lateral view; 3. ventral view.

FIGURES 7 – 14. Plagiosterna adamsii, last instar larva. 7. head; 8 – 9. mandibles; 10 – 11. antennae; 12. labrum; 13. epipharynx; 14. maxillae and labium.

FIGURES 23 – 24. Tibia and tarsungulus, last instar larva. 23. Plagiosterna adamsii; 24. P. aenea.

FIGURES 25 – 29. Schematic presentation of tubercular patterns (top: prothorax; middle: mesothorax; bottom: 2 nd abdominal segment). 25. first instar larva of Plagiosterna adamsii; 26. last instar larva of P. adamsii; 27. first instar larva of P. aenea; 28. last instar larva of P. aenea; 29. color variation of last instar larva of P. aenea.