SANE, S.P.; DIEUDONNE, A.; Univ. Of Washington, Seattle; Univ. Of Washington, Seattle: Neuroanatomy of antennal bristle fields in the hawk moth, Manduca sexta

Insect antennae are multi-sensory organs capable of detecting odor, humidity and temperature. Antennae also serve an important mechanosensory function via neurons that encode motion of their basal scape-pedicel joint. Across diverse insect taxa, this basic apparatus is tuned to enable a wide range of behaviors including wind detection among certain flying insects, tactile sensation in walking insects or auditory stimuli from mates or predators. In Lepidoptera, the antennae are equipped with two sets of mechanosensors. One set, the Johnston’s organs, are situated along the axis of the antenna spanning the scape-pedicel joint. A second set, the Bohm’s bristles, are located on the antennal surface and organized as pairs of bristle fields situated opposite to each other on scape and pedicel and are roughly orthogonal to the axis of joint motion. Thus, a motion in head capsule-scape or scape-pedicel joints stimulates these bristle fields as they brush against the inter-segmental cuticular folds. Although well located to encode antennal movement, little is known about the innervation pattern of the underlying neurons or their mechanosensory role during flight. To study the neuroanatomy of Bohm’s bristles in the hawk moth Manduca sexta, we injected the bristle fields with a fluorescent dye and observed their innervation patterns under a confocal microscope. The images reveal axonal projections from unipolar sensory neurons situated at the base of the Bohm’s bristles into the antennal nerve. En route to the antennal nerve, the axons form a bundle that terminates in an area of the brain innervated by dendrites of antenno-motor neurons. Our results suggest that this area may be the site of sensory-motor integration of antennal response to stimulation of Bohm’s bristles. This work was supported by an Office of Naval Research grant to Tom Daniel.