Ilybius biguttulus Germar

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 : 40

Ilybius biguttulus Germar

Instar I. Colour. Head dorsally with a pattern of light­brown and paleyellow areas; head appendages grey to brown. Thorax and abdomen grey. Legs, urogomphi and ventral body surface pale brown. Head ( Fig. 1A ). HL 5 1.07 mm, HW 5 0.93 mm. Sides of head parallel. Legs ( Fig. 3 ). Tibia and tarsus of each leg with ventral spinulae. Femora AV series with spinulae; PV series with two proximal setae. Abdomen ( Fig. 2A ). LAS 0.5 times UT. Siphon long (SI/LAS 5 .41). Terga 1–7 with dark spiniform setae; each tergum with two dorsal and two ventral submedial and one lateral setae on each side. Sterna 1–3 with two small pale submedial setae; sterna 4–7 with two dark submedial spiniform setae, other small setae present but not prominent. Urogomphus with U4 and U3 spiniform and pale, U3 short (length of U4/length of U3 5 0.51), U2 setiform and elongate.

Instar III. Colour ( Fig. 6A ). Head with distinct dark brown and pale yellow areas. Body dorsally brown to grey with lateral and sub­lateral pale spots on each segment. Head ( Fig. 7A ). HL 5 2.09 mm, HW 5 1.89 mm. Sides of head parallel. Legs ( Fig. 8 ). Femora with secondary dorsal spines as follows: profemur four to six; mesofemur—four to five; metafemur five to seven; femora with spinulae in AV series. Abdomen ( Fig. 11A ). LAS 0.69 times UT. Abdomen with dorsal surface bearing numerous spiniform setae; primary setae setiform.

Ecology. Ilybius biguttulus adults and larvae were collected in small pools and along the edges of larger ponds. In all cases they occurred among the aquatic vegetation and in sites where water levels were variable. Collected female adults laid eggs that hatched in late September. Collected instar I larvae were found in late August and early September. These records support the life history proposed by Hicks and Larson (1995) for this species.

Figures

Fig. 1. Dorsal surface of the head of instar I larvae of three species of Ilybius Erichson. A I. biguttulus, B I. discedens, C I. pleuriticus.

Fig. 3. Ilybius biguttulus. Instar I, right legs, anterior and posterior aspects.

Fig. 2. Last three abdominal segments and urogomphi, dorsal aspect, of instar I larvae of three species of Ilybius Erichson. A I. biguttulus, B I. discedens, C I. pleuriticus.

Fig. 6. Dorsal body surface of instar III larvae of three species of Ilybius Erichson. A I. biguttulus, B I. discedens, C I. pleuriticus.

Fig. 7. Dorsal body surface of head of instar III larvae of three species of Ilybius Erichson. A I. biguttulus, B I. discedens, C I. pleuriticus.

Fig. 8. Ilybius biguttulus. Instar III, right legs, anterior and posterior aspects.

Fig. 11. Last two abdominal segments and urogomphi, dorsal aspect, of instar III larvae of three species of Ilybius Erichson. A I. biguttulus, B I. discedens, C I. pleuriticus.