Pleurota bicostella

Pleurota bicostella (Clerck, 1759)

Barcode Index Number: BOLD:ADD4880

Table 1, Figs. 1–2, 33–34, 51, 65

Phalaena bicostella Clerck, 1759: pl. 3, fig. 15. Type locality: Scandinavia? Lectotype (NHMUK, not examined) designated by Robinson & Nielsen (1983), who did not indicate the sex.

Pleurota bicostella ab. adscriptella Krulikowsky, 1908: 18.

Material studied. 2 ♂ (DNA sample 00060 Lepid. Phyl; DNA sample 00061 Lepid. Phyl), Finland, PPp: Kiiminki, 29.VI.2006, M. Mutanen leg. (coll. MUT); 34 ♂ (GP 5310 J. Tabell; GP 5881 J. Tabell; DNA sample 23700 Lepid Phyl), 6 ♀ (GP 5477 J. Tabell; GP 5672 J. Tabell; GP 5945 J. Tabell; GP 6026 J. Tabell), Finland, EH: Hartola 682:344, 4.VII.2014 – 26.VI.2018, J. Tabell leg. (coll. TAB); 1 ♂ (GP 5569 J. Tabell, DNA sample 24663 Lepid Phyl), Russia, Buryatia, 53°13’N 109°19’E, Barguzin valley 1000 m, Ust-Barguzin-Yambui rd. taiga, 13.VII.1996, Jalava & Kullberg (coll. MZH); 1 ♂ (slide Sihvonen 2786), Finland, Kerimäki, Riitasensuo, 2.VII.1997, P. Sihvonen leg. (coll. SIH).

Diagnosis. Pleurota bicostella is a relatively large species (wingspan 20–24 mm) compared to most congeners. It is characterized by pale grey forewing mixed with white scales and distinct black discal and discocellular spots. In a rare aberration, P. bicostella ab. adscriptella Krulikowski, 1908, the forewing is darker, brownish grey without white irroration (Tokár et al. 2005). The moderately broad posterior lobe of juxta compared to related species and the crescent-shaped valval lobe in the male genitalia, and small posterior signa in the female genitalia are diagnostic.

Molecular data. Altogether one 657 bp and 22 full-length (658 bp) sequences of bicostella were available for genetic analysis. The results revealed 5.56 %–10.06 % divergences between bicostella and the other barcoded taxa of the bicostella species group (Table 1). The nearest neighbour to bicostella is a Moroccan species P. lepigrei Lucas, 1937, with a 5.56 % divergence. The barcodes of bicostella exhibit 1.08 % intraspecific variation.

Description. Adult. Wingspan 19.6–24.1 mm. Labial palpus off-white, ventrally and laterally brown, 6.5 x as long as diameter of eye (1 st and 2 nd palpomeres), 3 rd palpomere 0.3 x length of 1 st and 2 nd palpomeres. Scape of antenna off-white, flagellum brown. Head, thorax and tegula off-white to pale grey. Forewing pale grey, with scattered brown scales, discal, plical and discocellular spots distinct, blackish brown, fringe line with a few blackish brown flecks; costal line white, moderately broad, from base to 5/6; subcostal line brown, basally slightly narrower. Costal fringe brown, dorsal fringe pale brown, basally white. Hindwing pale brownish grey, margin pale brown, fringe pale brown. Abdomen pale grey, slightly lustrous, each segment with a transverse row of ochre scales.

Male genitalia. Uncus triangular from ventral view, as long as gnathos, lined with several long and short bristles, apex with parallel-sided stout protuberance. Gnathos subtriangular from ventral view, broad, surface of apical third covered with scobination. Valva slightly upwardly oblique from ventral view, ventral margin medially slightly bulged, costa almost horizontal; cucullus thimble-shaped; sacculus covered with several bristles; valval lobe well delineated, short, crescent-shaped, covered with several bristles, outer margin lined with small nodules. Juxta tuning-fork-shaped, robust; posterior lobe moderately broad, reaching base of uncus; phallus slightly arched, broad, with one plate-shaped cornutus surrounded by a patch of small spines. Vesica complex, containing small dorsal diverticulum, large ventro-basal diverticulum, ductus ejaculatorius making two distinct curves before opening laterally, large portion of surface covered with microtrichia.

Female genitalia. Papilla analis ovoid, covered with short and long bristles. Apophysis posterioris 2.8 x as long as papilla analis and 1.7 x as long as apophysis anterioris, which is 1.25 x as long as segment 8. Segment 8 quadrate, dorsolaterally reinforced by sclerotized band, distal half covered with several bristles, proximal margin broad, convex, caudal margin concave; ventral longitudinal sclerotization ovoid. Antrum longer than segment 8, moderately broad, partly sclerotized, posterior fourth membranous, anteriorly slightly tapered, with two crescentshaped opposite patches of different size and two narrow plates with several strongly sclerotized nodules. Ductus bursae moderately broad, membranous. Corpus bursae large, ovoid, with one arched broad signum bearing two narrow, long thorn-like protuberances, and two minute posterior signa.

Biology. The larva feeds on the leaves of Calluna and Erica in a silken web (Tokár et al. 2005).

Distribution. Widely distributed in the western Palearctic region.

Remarks: We illustrate the everted vesica of bicostella, possibly for the first time in genus Pleurota. The complex structure is indicative that the vesica potentially contains diagnostic characters that may bring additional resolution to the morphology-based taxonomy in the genus.