Ilybius vittiger (Gyllenhall)

Hicks, B. J. & Larson, D. J., 2000, Descriptions And Recognition Of Larvae Of Some Northern North American Species Of Ilybius Erichson (Coleoptera: Dytiscidae), The Coleopterists Bulletin 54 (1), pp. 36-59 : 49-53

Ilybius vittiger (Gyllenhall)

The larvae of this Holarctic species were described by Nilsson (1983). In North America this species occurs in the low arctic and boreal zone west of Hudson Bay. We did not examine larvae and therefore this species is not included in the multivariate analysis. To help with the recognition of this species from the others (by employing the key that follows), we extracted the diagnostic characters from the larval descriptions and diagrams of Nilsson (1983) and present them here.

Instar I. Colour. Dorsal surface of head and body generally grey. Head with paler spots on clypeus, epicranium and neck. Urogomphi yellowish gray. Sterna and legs pale yellow. Head. HL 5 0.90–1.00 mm, HW 5 0.72–0.84 mm. Head widened slightly at eyes. Terminal antenna segment (A4) length 5 0.70 of penultimate antenna segment. Legs. Femora with one proximal seta in the PV series. Ventral spinulae on all tibiae and tarsi. Femora with spinulae in AV series. Abdomen. Terga 1 to 7 with pale spiniform setae, two submedial and one lateral on each side. Sterna with spiniform submedial setae. LAS 5 0.44–0.51 mm; UT 5 0.96–1.07 mm. LAS/UT 5 0.40. Siphon long, SI/LAS 5 0.40. Urogomphus with U4 spiniform, pale in colour, length of U4/length of U3 5 0.30; U2 and U3 longer, setiform and darker.

Instar II. Colour. Dorsal surface of head and body dark grey with lighter spots. Legs light grey. Urogomphi yellowish grey. Head. HL 5 1.28–1.39 mm, HW 5 1.08–1.14 mm. Antenna with A4/A3 5 0.63; number of temporal spines four to five. Legs. Tibiae and trasi with ventral spinulae. Spinulae located in the AV series of the femora. Meso­ and meta­tibiae and tarsi with one to two dorsal setae. Abdomen. LAS 5 0.80–0.86 mm, UT 5 1.40–1.50 mm. LAS/UT 5 0.52. Siphon much shorter relative to instar 1, SI/LAS 5 0.17.

Instar III. Colour. Head and body dark grey with lighter spots. These spots evident on abdominal terga 1–5 and on last abdominal segment. Legs and urogomphi yellowish grey. Head. HL 5 1.70–1.80 mm, HW 5 1.44–1.50 mm; number of temporal spines four to five; antenna with A4/A3 5 0.53. Legs. Protibiae lacking dorsal setae, meso­ and metathoracic legs with 1–2 dorsal setae. Metafemur with AV spinulae. Abdomen. Tergal setation distinct, lateral tergal black setae on segments 2–10 almost as long as segment. LAS

5 1.36–1.44 mm; UT 5 1.70–190 mm; LAS/UT 5 0.72. Siphon short, SI/ LAS 5 0.10.