3145Wing-to-body articulation in insects is by a complex kinematic chain of several sclerites. It has three degrees of freedom: the wing flaps up and down and, in addition, forwards and backwards relative to the trunk; on transition between these phases, the moving wing blade flips (supinates) or flings (pronates) about its longitudinal axis. By opening from the rest position to the flight position, the wing spreads out (abducts) and, in certain insect orders, unfolds. The reverse adduction occurs on closing into the rest state (reviewed by Brodsky, 1994). Beetles have evolved complicated kinematics of wing unfolding (Schneider, 1978;Haas and Beutel, 2001).The elytra in beetles are the forewings, modified for a protective function. The rigid elytra reliably seal the wings and abdominal spiracles inside the subelytral space. This adaptation allows beetles to penetrate soil, bark, wood and water, an enriched diversity of ecological niches, and facilitates enormous adaptive radiation. Sealing is provided by many locks between the perimeter of the elytra and the body, between the elytra and the underlying wings and between the two elytra themselves (down their anal edges) or by the suture (see details and references in Discussion).Physiological study of elytral movement is hindered by the covert position of the mesothorax in beetles: for example, of the whole mesotergite, only the scutellum is exposed. Suggestions on the role of mesothoracical muscles were derived from anatomical observations on separate muscles, without understanding their action in concert.Mobility of the elytra is simple compared with that of the hind wings. Indirect fibrillar muscles, which drive the wings, are absent from the mesothorax. If elytra do beat in synchrony with wings during flight, they do so passively due to mechanical coupling between the meta-and mesothorax (Schneider and Meurer, 1975). Autonomous movements of elytra only occur during transitory opening and closing, driven by a limited set of direct and indirect elytral muscles.There exist several anatomical descriptions of how the elytra open and close (see details in Discussion), and these descriptions are sometimes contradictory. Previous cine The initial stage of opening included elevation of closed elytra (by 10-12°) and partition to the sides, combined with an inward turn (<2-3°). Axis of rotation at this stage presumably coincided with the AAA. Movement of one elytron with respect to the opposite one at the beginning of opening followed the shallow arc convex down. The geometry of this relative movement describes the initial partition of the elytra and release of the sutural lock.
