Plecia membranifera Hardy & Takahashi, 1960

Sutou, Mitsuaki, 2006, Immature stages of three Japanese species of the genus Plecia Wiedemann (Diptera: Bibionidae), Zootaxa 1223, pp. 1-18 : 8-9

Plecia membranifera Hardy & Takahashi, 1960

Description

Egg: Shiny brown, with slightly rough surface ( Fig. 3 A) observed at high magnification (×200–400), 0.58–0.67 mm long (n = 20).

First­instar larva: Head ( Fig. 3 C), yellowish brown; genae with 6 setae anteriorly, 2 sensory pits and 6 minute setae along posterior stem of ecdysial suture ( Fig. 3 C: 4–7), these minute setae sometimes disappear depending on condition of specimen; frontal apotome with 2 long and 2 short setae ( Fig. 3 C: 1–2); clypeus with 4 setae and 6 sensory pits dorsally, lateral projection of clypeus with short setae apically; labrum with 2 papillae and conical processes anteriorly; antennal plate relatively large in comparison to that of final­instar larva; mandible with 3 setae on basal half. Body ( Fig. 3 B) creamy white without processes, body segmentation of thorax indistinct, weakly arched in shape; brownish gut contents visible through translucent cuticle; only 1 pair of spiracles located posteriorly. Width of head capsule 0.20–0.23 mm (mean ± SD = 0.21 ± 0.01 mm, n = 20); Body length 1.0– 1.3 mm (mean ± SD = 1.2 ± 0.1 mm, n = 28).

Final­instar larva: Genae with 6 setae anteriorly, 2 minute setae and 14 sensory pits dorsally including 4 pairs along posterior stem of ecdysial suture ( Fig. 3 G: 4–7); genae and frontal apotome with some spotted maculae; frontal apotome with 2 setae and 4 sensory pits ( Fig. 3 G: 1–3). Clypeus with 4 setae and 6 sensory pits dorsally ( Fig. 3 G). Labrum with 2 small papillae dorsally, about 10 small papillae and fine setae on its anterior membranous part ( Fig. 3 G). Epipharynx ( Fig. 3 H) with many fine setae, small conical processes, 2 rows of denticles, 8 differentiated small papillae and 4 sensory pits. Mandible ( Figs. 3 I, J) with 3 blunt teeth (teeth may be rather worn by feeding activity), welldeveloped prostheca attached inside, 3 setae and 2 dorsal sensory pits on its basal half.

Cardo with 3 setae and sensory pit ventrally ( Fig. 3 M). Galeolacinia nearly trapezoidal in shape, with conical projection anteriorly ( Figs. 3 L, M); dorsal surface with fine setae, spinules, minute papilla, and 6–7 sensory pits ( Fig. 3 L); ventral surface with 2 setae and row of denticles anteriorly ( Fig. 3 M). Stipes composed of 3 parts: proximal isolated appendage, middle sclerite bearing seta and sensory pit with dorsal U­shaped invagination, and distal membranous ring with sensory pit and some spinules ( Figs. 3 L, M). Maxillary palpus with sensory pit and 10–12 apical papillae, one of which is slightly larger than others ( Fig. 3 M). Central membranous area of labium with 10–14 small papillae and fine setae on its anterior margin ( Fig. 3 K). Hypopharynx nearly elliptical in shape with some pubescence ( Fig. 3 K). Body brown, arrangement of processes as shown in Table 1 a. Platelike ventral swelling of prothorax ( Fig. 3 E) with 2 conical processes. Body cuticle covered with many spinules ( Fig. 3 F). Width of head capsule 0.74–0.88 mm (mean ± SD = 0.81 ± 0.05 mm, n = 9); Body length 12.8–17.1 mm (mean ± SD = 15.1 ± 1.4 mm, n = 15).

Pupa. Male ( Figs. 4 A, B): Vertex semicircular in frontal view; antenna slightly arched, lying transversely; maxillary palpus attenuated apically and extending transversely; rostrum short. Prothoracic spiracle vestigial. Extremities of hind legs reaching posterior part of 2nd abdominal segment. Arrangement of body processes as shown in Table 1 b, but dorsum of A2 and A7 each with only 2 setae in some specimens. Abdominal spiracles slightly protruded from body surface. Body length 6.9–8.5 mm (mean ± SD = 7.6 ± 0.4 mm, n = 13). Female ( Fig. 4 C): similar to male, but compound eye smaller, abdomen thicker than that of male. Body length 7.9–8.6 mm (mean ± SD = 8.4 ± 0.3 mm, n = 5).

Specimens examined

Egg: Laid by females reared from larvae collected on 19.III. 2001 in Korimoto, 31°34’N 130°32’E, 30 m alt., Kagoshima, Kagoshima Pref. First­instar larva: 28 examples (5 examples in NSMT), late May 2001, hatched from above eggs. Final­instar larva: 16 examples (3 examples in NSMT), 19.III.2001, same locality. Pupa: 13♂, 6Ψ (3♂, 2Ψ in NSMT), reared from larvae collected on 19.III. 2001 in same locality.

Ecological notes

This is a rare species, evidenced by the fact that this is only the second record of this species since its original description. Its distribution appears to be restricted to Kagoshima Prefecture, the southernmost part of Kyushu Island. The gregarious larvae of this species, consisting of 103 individuals, were collected in March from soils in open habitat where the herb Hedera rhombea was dominant. Afterward, the reared adults emerged in mid­April. Adult males flying over a lawn near the site were collected in August 1999. Therefore, this species most likely produces two or three generations per year.

Figures

FIGURE 3. Plecia membranifera. A, microstructure of egg surface. B, C, first­instar larva. D – M, final­instar larva. B, habitus, lateral view. C, head, dorsal view. D, habitus, lateral view. E, plate­like ventral swelling of prothorax. F, spinules on dorsum of fourth abdominal segment. G, head, dorsal view. H, epipharynx. I, right mandible, dorsal view. J, right mandible, inner view. K, labium and hypopharynx, ventral view. L, left maxilla, dorsal view. M, left maxilla, ventral view. See Fig. 1 for abbreviations. Scales: G, 0.5 mm. C, F and H – M, 0.1 mm.

FIGURE 4. Plecia membranifera, pupa. A, male, frontal view. B, male, lateral view. C, female, lateral view. See Fig. 2 for abbreviations.