Form, function and mechanics of femoral chordotonal organs in insects

Insect legs function as locomotory organs as well as highly sensitive multisensory probes. Specifically, they contain mechanosensory femoral chordotonal organs (FeCO) that monitor femorotibial movements and mediate behaviours ranging from local leg reflexes to whole-body movements. The structure and material properties of FeCO prefilter incoming mechanical signals, which are encoded by the underlying mechanosensory neurons. FeCO consists of functionally specialised subunits within which pairs of neurons are organised into scolopidia that connect to tibia via a receptor apodeme, an invagination of the tibial cuticle. In some hemimetabolous insects, the apodeme connects to individual scolopidia at different points, activating them at different tibial positions and mechanically fractionating the stimulus range. However, in some holometabolous insects, mechanical stimulus is channelled into different components and directed to various FeCO subunits. FeCO thus serves as an ideal mechanosensory organ to study the role of structure in determining sensory function.