Proprioceptive activity of the wing-hinge stretch receptor in Manduca sexta and other atympanate moths : a study of the noctuoid moth ear B cell homologue

A multiterminal neurone, recently identified at the wing-hinge of the atympanate moth Manduca sexta, is shown to respond as a proprioceptor monitoring elevatory movements of the hind wing. Extracellular recordings from the individual receptor axon confirm this cell to be the source of the spontaneous and regular discharge observed in previous recordings of peripheral nerve 3N1b1. When the wing is raised, this tonic discharge rate increases proportionally with the angle of elevation. When the wing is displaced sinusoidally at a low frequency, the receptor discharge is modulated throughout the wing beat, increasing steadily to a maximum at the top of the upstroke, then slowly decreasing to a minimum at the bottom of the downstroke. At higher wing-beat frequencies, a phasic burst of activity occurs near the top of the upstroke, followed by a silent period during the downstroke. Video-microscopic observations of the wing-hinge during active, stationary flight suggest that the receptor is stimulated by the stretching of its peripheral attachment, the subalar membrane. Stretch receptor sensitivity to wing movement is demonstrated in representatives of 4 lepidopteran families, suggesting that the proprioceptive response is widespread among the Lepidoptera. The functional role of the wing-hinge receptor, and its proposed homologous relationship to both the B cell of the noctuoid moth ear, and the locust wing-hinge stretch receptor are discussed.