THE NEUROETHOLOGY OF SOUND PRODUCTION IN TIGER MOTHS (LEPIDOPTERA, ARCTIIDAE) .2. LOCATION OF THE TIMBAL CENTRAL PATTERN GENERATOR IN CYCNIA-TENERA HUBNER

When stimulated either acoustically or tactually, certain species of a rctiid moths rhythmically emit trains of clicks from metathoracic tymb als. The purpose of the experiments presented here was to determine th e location within the central nervous system (CNS) of the proposed tym bal central pattern generator (CPG) in Cycnia tenera. Motor neuron imp ulses that underlie tymbal activation were recorded extracellularly fr om the tymbal nerve while moths were subjected to selective severing o f the suboesophageal, prothoracic, pterothoracic and abdominal ganglia connectives. Motor output evoked by either acoustic or tactile stimul ation originates from a common CPG because tymbal nerve spikes in both cases are similar in amplitude, waveform and rhythmicity. Our results showed: (1) removal of the CNS posterior of the second abdominal neur omere had no effect, (2) removal of the head decreased the responsiven ess of the animal to acoustic stimulation and, (3) severing the connec tives between the prothoracic and pterothoracic ganglia abolished resp onses to acoustic stimuli and diminished responses to tactile stimuli. We conclude that although the minimal circuitry sufficient for activa ting the tymbals resides in the pterothoracic ganglion, the prothoraci c and cephalic ganglia are required for the normal, and in particular, auditory-evoked operation of the tymbal CPG.