The neural mechanisms of antennal positioning in flying moths

SUMMARY In diverse insects, the forward positioning of the antenna is often among the first behavioral indicators of the onset of flight. This behavior may be important for the proper acquisition of the mechanosensory and olfactory inputs by the antennae during flight. Here, we describe the neural mechanisms of antennal positioning in hawk moths from behavioral, neuroanatomical and neurophysiological perspectives. The behavioral experiments indicated that a set of sensory bristles called Böhm's bristles (or hair plates) mediate antennal positioning during flight. When these sensory structures were ablated from the basal segments of their antennae, moths were unable to bring their antennae into flight position, causing frequent collisions with the flapping wing. Fluorescent dye-fills of the underlying sensory and motor neurons revealed that the axonal arbors of the mechanosensory bristle neurons spatially overlapped with the dendritic arbors of the antennal motor neurons. Moreover, the latency between the activation of antennal muscles following stimulation of sensory bristles was also very short (<10 ms), indicating that the sensorimotor connections may be direct. Together, these data show that Böhm's bristles control antennal positioning in moths via a reflex mechanism. Because the sensory structures and motor organization are conserved across most Neoptera, the mechanisms underlying antennal positioning, as described here, are likely to be conserved in these diverse insects.