Spatial arrangement of Böhm's bristles and resolution of joint position in cricket antennae (Acheta domesticus L.) (Orthoptera: Gryllidae)

Böhm's bristles are mechanosensory structures located on the basal segments of antennae of most insects and provide sensory feedback for antennal positioning. It is generally assumed that the bristles provide sensory information about the joint angles as the bristles are positioned such that they are mechanically deflected by the reconfiguring flexible cuticle of the joint. If the Böhm’s bristles are only detecting joint position, and the full range of motion of that joint is detected by the array of Böhm’s bristles, then the extent of the array should correspond to the length of the segment covered by the flexible cuticle during bending. The spatial arrangement of the bristles could then provide insight into the joint movement range, joint type, and the resolution of the joint angle available as sensory input. To evaluate this, we characterized the Böhm's bristles arrangement compared to the joint excursion in A. domesticus (two hinge joints) using scanning electron microscopy (SEM). Our SEM analysis revealed one field of Böhm's bristles on the dorsal side and two on the ventral side of the scape, and two additional fields of Böhm's bristles on the lateral and medial sides of the pedicel. The bristles are positioned such that they are all deflected when the scape or pedicel is completely bent; thus, the arrangement of bristles matches the range of joint movement. In addition, we suggest that the number of bristles in the direction of joint movement indicates the resolution of detection of the movement of the joint.