Portevinia maculata (Fallén, 1817):52

Portevinia maculata (Fallen, 1817).

Fallen, C.F. (1816-1817) Syrphici Sveciae. Pp. 1-14 [1816.06.08], 15-22 [1816.06.08], 23-30 [1817.05.10], 31-42 [1817.05.20], 43-54 [1817.05.21], 55-62. [1817.05.22] Berlingianis, Lundae [= Lund].

The single European species of Portevinia was until recently usually consigned to Cheilosia (Speight 2010). In the paper in which Goffe (1944) introduces the name Portevinia he also defines the genus. More recently, Thompson (1980) has claimed that two other Palaearctic Cheilosia species (C. altaica Stack. and C. dispar Hervé-Bazin) should also be consigned to Portevinia (Speight 1986).

Synonym:

Eristalis maculata Fallen, 1817: 52.

Flowers visited by adults: Allium ursinum, Ranunculus, Rubus idaeus (Speight 2010).

The larva of P. maculata is phytophagous, mining firstly the stem-base and later the corms of A. ursinum (or A.t riquetrum). In the literature it is frequently referred to, erroneously, as mining the leaves of A. ursinum. In alpine grassland, P. maculata presumably uses a different Allium species as foodplant, as is the case in Cheilosia fasciata, though which Allium is involved (probably A. victorialis: U. Schmid pers.comm. in Speight 2010) does not seem to have been established for P. maculata. The larva may be distinguished from the larvae of related genera by the keys incorporated into Rotheray (1993).

Flight period: from end of April to June and July at higher altitudes (Speight 2010).

This species ranges from southern Norway south to north Spain; from Ireland eastwards into central Europe as far as Liechtenstein, Austria and northern Italy (Speight 2010).

Adults inhabit areas of the woodland floor with dappled sunlight and plants of Allium ursinum or (less frequently) A. triquetrum; edges of clearings, beside brooks and along tracks with either of these Allium species; adults fly low around and among stands of Allium, often settling on the leaves of this plant, or on adjacent vegetation; rarely found away from the immediate vicinity of A. ursinum plants. Where it has been naturalised in parkland etc, A. triquetrum may occur in dense stands like A. ursinum, and then provides an alternative foodplant for Portevinia (Speight 2010).

Preferred environment: forest; alluvial hardwood forest and humid Fagus or Quercus forest; also unimproved alpine grassland (Speight 2010).

Larva has been described and figured by Speight (1986b) and illustrated in colour by Rotheray (1994).

Larva (from Speight 1986).

Length: 8-9 mm., width (max.) 2.5-3.0 mm.

Description: more or less cylindrical, with a flattened ventral surface, uniformly off-white in colour; tapering anteriorly, abruptly truncated posteriorly, the body terminating in art almost flat disc of tissue, into which the last abdominal segment is incorporated. General body surface covered in minute, close-set, recurved spinules of rather uniform size, except on the terminal disc of the abdomen, from which they are absent. Terminal disc smooth and featureless, except for posterior spiracular process.

Head: antenno-maxillae well developed, visible as a pair of tubular processes each side of the mid-line, at the anteroventral extremity ofthe larva; dorsal lip (sensu Hartley 1961) a simple membranous flap; tips of large, heavily sclerotised mouth-hooks prominent externally; ventral pocket beneath mouth not apparent.

Thorax: tapering, posteriorly nearly the same width as the abdomen; anterior fold of the prothorax (sensu Hartley 1961) complete; lateral lobes of the prothorax evident beside the mouth, but not prominent; prothoracic, spiracular processes weakly sclerotised, simple tubes, short and narrow, placed dorso-laterally and carried part-concealed in pockets in the body-surface; thoracic segmental setae distributed as on abdominal segments, except that only 1 pair of dorso-lateral setae could be detected on each segment; prolegs absent on thorax.

Abdomen: seven segments detectable (from segmental setae) ventrally, six dorsally; primordia of pupal spiracles obvious on dorsal surface of abdominal segment 1; seventh abdominal segment modified to form, with eighth segment, the disc of tissue terminating the abdomen posteriorly; posterior spiracular process sessile, 3-4 x as wide as long, brightly shining, black, its spiracular disc almost flat, with a mirror-like surface shine, the spiracular slits four per side, each a simple horse-shoe shape with its ends pointing toward the periphery of the disc; 2 pairs of dorso-lateral, 3 pairs of ventro-lateral and 2 pairs of ventral segmental setae carried by each segment (except seg. 7, where the dorso-lateral setae cannot be detected), those of segment 8 forming part of the fringe of setae rimming the terminal disc ofthe abdomen; segmental setae decreasing in length imd strength towards the anterior end of the larva; prolegs (and their associated crochets) and lappets absent from abdominal segments.

Puparium (from Speight 1986).

Length c. 7.00 mm; unicolourous pale brown, except for black, shining, posterior spiracular process, shape and surface m.orphology very similar to that of larva, except that puparium is anteriorly more blunt-ended; puparial horns; posterior disc and spiracular process as in larva.