Immature stages of three Japanese species of the genus Plecia Wiedemann (Diptera: Bibionidae) Author Sutou, Mitsuaki text Zootaxa 2006 1223 1 18 journal article 10.5281/zenodo.172619 fc2cfbf1-64f7-401d-8752-9bef74bc7eee 1175­5326 172619 Plecia adiastola Hardy & Takahashi, 1960 Description Egg : Shiny brown with smooth surface ( Fig. 1 A), 0.53–0.65 mm long ( n = 20). Final­instar larva : Genae with 6 setae anteriorly and 18 sensory pits dorsally including 8 sensory pits along posterior stem of ecdysial suture ( Fig. 1 G: 4–7). Frontal apotome with 2 setae anteriorly, 2 minute setae posteriorly, and 2 sensory pits between them ( Fig. 1 G: 1–3). Clypeus with 4 setae and 6 sensory pits dorsally ( Fig. 1 G). Labrum with 2 minute setae and 2 sensory pits dorsally, about 10 small papillae and fine setae on its anterior membranous part ( Fig. 1 G). Epipharynx ( Fig. 1 H) with many fine setae, small conical processes, 8 differentiated small papillae and 4 sensory pits. Mandible ( Figs. 1 I, J) with 3 large and 2 small teeth, well­developed prostheca attached inside, 3 setae and 2 dorsal sensory pits on its basal half. Cardo with 3 setae and sensory pit ventrally ( Fig. 1 M). Galeolacinia nearly quadrilateral in shape, with conical projection and 2–3 small papillae on anterior margin ( Figs. 1 L, M); dorsal surface with many fine setae, spinules, and 5–7 sensory pits ( Fig. 1 L); ventral surface with 1 seta ( Fig. 1 M). Stipes composed of 3 parts: proximal isolated appendage, middle sclerite with seta and sensory pit, and distal membranous ring with sensory pit ( Fig. 1 M). Maxillary palpus with sensory pit and 11–13 apical papillae, 1 or 2 of which slightly longer than others ( Fig. 1 M). Central membranous area of labium with 12–14 small papillae and fine setae on its anterior margin ( Fig. 1 K). Hypopharynx nearly wing­like in shape with some pubescence ( Fig. 1 K). Body dark brown, arrangement of processes as shown in Table 1 a, but following deformations were found in some specimens: number of lateral processes of T3 only 4, posterior row of ventral processes of A1 and A2 absent. Plate­like ventral swelling of prothorax ( Fig. 1 C) with 3 processes, central one smaller than lateral ones. Body cuticle covered with many spinules ( Fig. 1 D). Width of head capsule 0.68–0.92 mm (mean ± SD = 0.78 ± 0.06 mm , n = 67; Fig. 7 a); Body length 11.7–16.7 mm (mean ± SD = 14.2 ± 1.5 mm , n = 66). Pupa . Male ( Figs. 2 A, B): Vertex uneven in frontal view; antenna arched, extending obliquely; maxillary palpus extending laterally; rostrum short. Extremities of hind legs reaching posterior margin of 2nd abdominal segment or anterior margin of 3rd abdominal segment. Arrangement of body processes as shown in Table 1 b, but venter of A3 with 2 setae in some specimens. Abdominal spiracles flat, not protruded from body surface. Body length 6.3–10.0 mm (mean ± SD = 8.5 ± 1.0 mm, n = 26). Female ( Fig. 2 C): similar to male, but compound eye smaller, abdomen thicker than that of male. Body length 7.6–11.1 mm (mean ± SD = 9.5 ± 0.7 mm , n = 24). Specimens examined Egg : Laid by females reared from larvae or pupae collected on 29.III.1998 and 17.IV. 2001 in Tokiwadai, 35°28’N 139°35’E , 60 m alt., Hodogaya ward, Yokohama, Kanagawa Pref. and on 29.IV. 2000 in Mt. Inao, 31°07’N 130°53’E , 600 m alt., Sata, Kagoshima Pref. Final­instar larva : 14 examples, 6.V.2003 , Mukaiyama, 38°14’N 140°52’E , 70 m alt., Taihaku ward, Sendai, Miyagi Pref.; 6 examples, 29.III.1998 , 21 examples, 17.IV.2001 , 18 examples (10 examples in NSMT), 5.XII.2002 , 14 examples, 4.IV.2003 , Tokiwadai, Yokohama; 5 examples, 9–10.III.2000 , Shiroyama, 31°35’N 130°32’E , 60 m alt., Kagoshima, Kagoshima Pref. Pupa : 13♂ , 14Ψ ( 5♂ , 5Ψ in NSMT), reared from larvae collected on 6.V. 2003 in Mukaiyama, Sendai; 2♂ , 2Ψ, 10.V.1998 , Tokiwadai, Yokohama; 4♂ , 5♂ and 3Ψ, reared from larvae collected on 29.III.1998 and 17.IV.2001 respectively in Tokiwadai, Yokohama; 3Ψ, reared from larvae collected on 9–10.III. 2000 in Shiroyama, Kagoshima; 3♂ , 2Ψ, 29.IV.2000 , Mt. Inao, Sata. Ecological notes The distribution of this species appears to be restricted to Japan . In the plains of central Japan , the adults emerge from mid­May to early June, and the final­instar larvae develop beyond the winter (univoltine). The larvae and pupae are usually gregarious in soil. The number of individuals in a single cluster ranged from 23 to 96 in the present study. The larvae of this species prefer damp soil in a forest, e.g., directly under rotting wood. According to Krivosheina (1998) , the larvae of the closely related species P. thulinigra live in rotting wood at the final stage of decomposition in Far East Russia . Many males of P. adiastola were observed walking on piles of decayed wood trying to mate with females ( 29. V. 2000 , Hachioji, Tokyo). Flight activity was rarely seen in this species, but several males were once observed flying during daylight hours ( 25–26. V. 2001 , Yokohama).