Ilybius subaeneus Erichson, 1837

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 : 53-54

Ilybius subaeneus Erichson

The larvae of this Holarctic species were described by Bertrand (1928) and Galewski (1966). We did not examine larvae and therefore the 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 Galewski (1966) and present them here.

Instar I. Colour. Dorsal surface of head and body brown. Head with characteristic pattern having large pale areas. Head. HL 5 0.96–1.02 mm, HW 5 0.86–0.97 mm. Terminal antenna segment (A4) length 5 0.67 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 1–7 with pale spiniform setae, two submedial and one lateral on each side. Sterna with spiniform submedial setae. LAS 5 0.75–0.85 mm; UT 5 1.40–1.60 mm. LAS/UT 5 0.53. Siphon long, SI/LAS 5 0.35. 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 brown to light brown. Head with large pale areas. Head. HL 5 1.56–1.59 mm, HW 5 1.36–1.37 mm. Antenna with A4/A3 5 0.64; number of temporal spines four to six. Legs. Tibiae and trasi with ventral spinulae. Spinulae located in the AV series of the femora. Abdomen. LAS 5 1.17–1.30 mm, UT 5 2.15–2.22 mm. LAS/ UT 5 0.55. Siphon much shorter relative to instar I, SI/LAS 5 0.28.

Instar III. Colour. Dorsal surface of head and body brown to olive­brown. Head with large pale areas. Head. HL 5 2.15–2.18 mm, HW 5 1.90–1.94 mm. Antenna with A4/A3 5 0.43. Number of temporal spines five to seven. Sides of the head narrowing anteriorly. Legs. Metafemur with AV spinulae. Dorsal setae on all tibiae and tarsi. Abdomen. LAS 5 2.25–2.30 mm, LAS/ UT 5 0.75. Siphon short, SI/LAS 5 0.18.

Keys to Larvae of Known North American Ilybius Key to the larval instars (Modified from Galewski 1966)

1 Head without temporal spines; abdomen segment 7 with ventral side membranous, not sclerotized; siphon elongate, SI/LAS. 0.35 ------------ Instar I

1 9 Head with temporal spines; abdomen segment 7 with ventral side sclerotized; siphon not as elongated, SI/LAS,.33 ------------------------------------------- 2

2(1) Mandibles without emargination on their outer edge ( Fig. 12A ) ----------------------------------------------------------------------------------------------------------------------------- Instar II

2 9 Mandibles with a distinct emargination on their outer edge ( Fig. 12B ) ----------------------------------------------------------------------------------------------------------------------------- Instar III

Figures

Fig. 12. Left mandible of instar II (A) instar III (B) larvae of Ilybius.