Cheilosia vernalis (Fallén, 1817)

Cheilosia vernalis (Fallén, 1817) View in CoL immature stages

Description

First stage larva (L1) ( Fig. 3 View Fig )

Length: 2.4 mm; width: 0.75 mm; height: 0.68 mm (n = 1). The 8 th abdominal segment (anal segment) with two pairs of lappets. Oval in cross-section and flat ventrally with one pair of poorly developed crochet-less locomotory organs in the mesothorax and in the 1 st and 7 th. Head with well-developed antenno-maxillary organs. Anterior part larger than the posterior part. Colour: yellowish. PRP: light yellowish. Wrinkled surface above, smooth surface below transverse ridge.

Second stage larva (L2) ( Fig. 4 View Fig )

Length: 4–4.34 mm; width: 1.32–1.5 mm; height: 1.32 mm (n = 2). Colour: light brown. Head skeleton ( Fig. 5 View Fig ). One pair of heavily sclerotized mouth-hooks. A pair of small accessory teeth located behind the mouth-hooks. Labrum, mandibular apodeme, mandibular lobe and tentorial bar heavily sclerotized. Mandibular apodeme and mandibular lobe fused. Tentorial arm not sclerotized. Dorsal cornu almost two thirds of the length of the ventral cornu. PRP: fused and shiny yellowish-brown, with a noticeable transverse ridge. Surface above transverse ridge with wrinkles, surface below smooth. Length above transverse ridge: 0.18–0.28 mm; length below transverse ridge: 0.04–0.07 mm; width at the transverse ridge: 0.30–0.38 mm.

Third stage larva (L3) ( Fig. 6 View Fig )

Length: 6.72 mm; width: 2.15 mm; height: 2.02 (n = 1). The 8 th abdominal segment (= anal segment) with two pairs of lappets. Oval in cross-section and flat ventrally, with one pair of poorly developed crochet-less locomotory organs in the mesothorax and in the 1 st and 7 th abdominal segments. Head with well-developed antenno-maxillary organs. Colour: dark brown. ARP: cylindrical, tapering with a fanshaped tip with seven spiracular openings. PRP ( Fig. 7 View Fig ): shiny light brown with a slightly noticeable transverse ridge. Length above the transverse ridge: 0.25 mm; length below transverse ridge: 0.13 mm; width at the level of the transverse ridge: 0.32 mm. Surface above the transverse ridge with wrinkles and punctures; surface below the transverse ridge with smooth surface. Spiracular plate ( Fig. 7B View Fig ) with four pairs of long interspiracular setae, one pair of perispiracular glands, four pairs of irregular spiracular openings, and small groove at the center of the spiracular plate. A pair of ecdysial scars located in the middle of the spiracular plate. Chaetotaxy ( Fig. 8 View Fig ): all observed sensilla bearing a seta. Prothorax: eight pairs of sensilla. Mesothorax: dorsally with three pairs of sensilla, laterally with three pairs of sensilla, and ventrally with two pairs of sensilla. Metathorax: dorsally with three pairs of sensilla, laterally with three pairs of sensilla, and ventrally with two pairs of sensilla. Abdomen: 1 st to 6 th abdominal segments: dorsally with three pairs, laterally with five pairs and ventrally with three pairs of sensilla. 7 th abdominal segment: dorsally with three pairs, laterally with five pairs and ventrally with three pairs around the anus. The anal segment with nine pairs of sensilla observable.

Puparium ( Fig. 9 View Fig )

Length: 5.44–6.44 mm; width: 2.19–2.85 mm; height: 1.98–2.54 mm (n = 4). Colour: light brown. PRP: same as the L 3 larva. Length above the transverse ridge: 0.14–0.15 mm; length below the transverse ridge: 0.32–0.44 mm; width at the level of the transverse ridge: 0.37–0.39 mm. Pupal spiracles ( Fig. 10 View Fig ): length: 0.45 mm; width: 0.17 mm; space between the tips of the pupal spiracles: 1.9 mm. Dark-brown colour; cylindrical, tapering with a rounded tip; surface covered with tubercles except at the base. Smooth surface at the base. Tubercles with five to eight opening holes. PRP: same as the L3. Length above the transverse ridge: 0.27 mm; length below the transverse ridge: 0.13 mm. Chaetotaxy: same as the L3.

Intraspecific variation within Cheilosia vernalis immature stages

One adult of C. vernalis emerged from a puparium that showed some morphological variation in the colour of the pupal spiracles, exhibiting a light-yellow hue ( Fig. 11A View Fig ), and the surface of the PRP, almost completely smooth and with a constriction ( Fig. 11B–C View Fig ). After a molecular study analysing sequences from Danish immature stages of C. vernalis with the morphology stated in the above description, the Danish puparium with different pupal spiracles and PRP, as well as sequence from adults of C. vernalis from different Spanish localities, we concluded that the puparium with a different morphology belonged to the clade of C. vernalis / C. reniformis ( Fig. 12 View Fig ). As the presence of C. reniformis has not been confirmed in Denmark, but C. vernalis is widespread in this country, and given the morphological similarity between these two species, we conclude that the odd puparium belongs to the species C. vernalis too.