Mechanosensory role of elytra in beetle flight

Elytra, the modified and hardened forewings of Coleoptera, represent a key innovation in insect evolution, and can serve varied roles in physical protection, thermoregulation, water balance, transport of symbionts, sexual selection, and stridulation. However, in spite of their evolutionary origin as wings, the current role of elytra in flight has long been thought to be minimal. Here, we demonstrate a novel mechanosensory function for elytra in beetle flight by quantifying biomechanical changes during take-off following sequential elytral ablation in a False Blister Beetle (Sessinia livida, Oedemeridae). Elytral ablation to any extent resulted in loss of flight control for body orientation, an outcome also observed in dipterans with modified halteres. However, and unlike haltere manipulation in Diptera, elytral ablation yielded no changes in either wingbeat frequency of the hindwings or in oscillation frequency of the elytra. The elytra thus actively participate as sensory organs regulating flight control and likely function gyroscopically, albeit less effectively than dipteran halteres. A gyroscopic role for elytra may underlie evolutionary patterns of forewing shortening in beetles, and the substantial comparative diversity of this structure suggests a correspondingly wide range of sensory and biomechanical functions among the Coleoptera.