1. The phonotactic threshold of 3 to 5-day-old adult female Acheta domesticus and the threshold of the L1 auditory neuron drop progressively (Fig. 1). 2. Application of juvenile hormone III (JHIII) to 1 -day-old females caused both the female's threshold for phonotaxis and the threshold of the L1 auditory neuron to drop 20 or more dB over the next 12 h (Figs. 3, 4). 3. JHIIFs effect on phonotactic threshold could be blocked by injection with a transcription (α-amanitin) or a translation blocker (emetine, Fig. 3). 4. Injection of emetine also prevented the JHIII induced drop in L1's threshold (Fig. 4). 5. Application of JHIII to the surface of, or microinjection of JHIII into one prothoracic hemiganglion caused the female to circle phonotactically away from the side of hormone addition at thresholds 25 to 35 dB lower than the pre-JHIII addition threshold within 2 h (Fig. 6). 6. Application of JHIII to the surface of both prothoracic hemiganglia, accompanied by microinjection of emetine into one hemiganglion resulted in the female circling phonotactically toward the side receiving emetine injection, with a 25 to 35 dB drop in threshold (Fig. 6). © 1991 Springer-Verlag.