Ilybius discedens Sharp

Instar I. Colour. Head brown with light brown areas; antennae grey with the terminal segment pale. Thorax, abdomen and urogomphi brown to grey. Sterna and legs pale yellow. Head (Fig. 1B). HL = 0.95 mm, HW = 0.89 mm. Head widened slightly at eyes. Legs (Fig 4). Femora with or without ventral spinulae, if present not numerous and located between AV setae; femur with one proximal seta in PV series. Abdomen (Fig. 2B). LAS 0.60 times UT. Siphon long, SI/LAS = 0.42. Urogomphus with U4 pale and spiniform, U3 and U2 darker and setiform, length of U4/length of U3 = 0.16. Abdomen with terga 1–6 each with two short, pale submedial setiform setae; lateral setae short; segment 7 with two dorsal and two ventral submedial setae and two darker, more elongate lateral setae, these setae much shorter than those of I. biguttulus or I. pleuriticus; other smaller setae present but not prominent.

Instar III. Colour (Fig. 6B). Head brown with light brown areas; appendages light­brown. Thorax and abdomen brown to grey with pale areas laterally except last three segments of abdomen without pale areas. Sterna light grey. Urogomphus brown. Legs light­brown. Head (Fig. 7B). HL = 1.73 mm, HW = 1.53 mm. Sides of head parallel. Legs (Fig. 9). Femora with secondary dorsal spines as follows: profemur four to six, mesofemur four to five, metafemur five to seven; pro­ and mesofemora with spinulae in the AV series but number and size of spinulae very reduced; metafemur without spinulae in AV series. Abdomen (Fig. 11B). Dorsal surface with relatively few spiniform setae. Primary setae of abdominal segments small and pale. LAS/UT = 0.86.

Ecology. Adults and larvae of I. discedens where collected in small Sphagnum bog pools where the water level remained constant. Instar I larvae hatched from eggs of field collected females in early and middle September. The incubation time for eggs reared in the lab at 23 ° C ± 1 ° was 13.3 ± 1.2 days (n = 37), similar to that reported by Hicks and Larson (1995). The collection records and hatch dates support the life history proposed by Hicks and Larson (1995) for this species.