The role of haltere campaniform sensilla in equilibrium reflexes of the fruit fly, <i>Drosophila melanogaster</i>

Flying animals use a combination of sensory modalities to maintain stable flight in the face of external and internal perturbations. Although insects rely extensively on vision for this task, members of the order Diptera possess specialized mechanosensory organs called halteres, which contain hundreds of strain-sensing campaniform sensilla that encode forces on the base of the structures as they oscillate during flight. Although the importance of halteres for flight stabilization is supported by past experiments involving surgical ablation or artificial manipulation, the requirement of the campaniform sensilla themselves has yet to be directly demonstrated. We investigated the role of haltere campaniform sensilla in the fruit fly, Drosophila melanogaster, by using a collection of Gal4 driver lines which are expressed in different populations of campaniform neurons, while recording the equilibrium responses of tethered flies subjected to rotation about their yaw axis. We show that the magnitude of the wing and head motor responses of flies decreases linearly with an increasing number of campaniform sensilla genetically silenced or ablated, providing direct evidence for the involvement of these mechanosensory structures in the detection of angular velocity during flight.