Ultrasonic startle behavior in bushcrickets (Orthoptera; Tettigoniidae)

Summary

• 1. In the present work, we show that in flight, bushcrickets not previously known to respond to ultrasound alter their flight course in response to ultrasonic stimuli. Such stimuli elicit in flying Neoconocephalus ensiger an extension of the front and middle legs along the body and a rapid closure of all 4 wings (Fig. 1). This is a short latency acoustic startle response to ultrasound, consistent with acoustic startle responses of other insects.

• 2. The percentage of trials on which acoustic startle responses were elicited was maximum (90%) for sound frequencies ranging from 25 to at least 60 kHz. No acoustic startle response was observed at frequencies of 5 or 10 kHz (Fig. 2). The threshold for the response was roughly 76 dB between 25 to 60 kHz (Fig. 2) and the behavioral latency was 45 ms (Fig. 3). Recordings from flight muscles show that they cease discharging during the acoustic startle response (Fig. 4).

• 3. The characteristics of the acoustic startle response match those of an auditory interneuron called the T-neuron. The frequency sensitivity of this neuron is greatest for sound frequencies ranging from 13 to 60 kHz (Fig. 6). Moreover, we found that the neuron produces many more spikes to ultrasound (30 kHz) of increasing intensitites than to a conspecific communication sound, whose dominant frequency is 14 kHz (Fig. 7).