Scirtes hemisphaericus uses macrophyte snorkels to pupate under water. With notes on pupae of additional European genera of Scirtidae (Coleoptera)

Abstract

Morphological and behavioural adaptations enable Scirtes hemisphaericus to pupate under water, using emergent macrophytes as snorkels to breathe atmospheric air. The last instar larva bites into emergent macrophytes until the aerenchym is exposed. The pupa pushes its fore body into the wound, becoming surrounded by an air film in continuity with intracellular and atmospheric air. The pupa lacks normal ecdysial sutures, instead, its cuticle ruptures between the pro- and mesothorax. The fore body cuticle remains in place, preserving the connection to atmospheric air for the immature beetle. Pupation in earthen cells is known only in Elodes. Several other genera pupate under some cover, or freely exposed. Most pupae have 2–4 horn-like pronotal processes and 2–4 caudal attachment organs which differ between genera and sexes. Hydrocyphon (which pupates under water) and S. hemisphaericus pupae lack pronotal horns and attachment organs.