Greater wax moths (Galleria mellonella L., Pyraloidea) use ultrasound sensitive ears to detect clicking conspeci®cs and echolocating bats. Pyralid ears have four sensory cells, A1±4. The audiogram of G. mellonella has best frequency at 60 kHz with a threshold around 47 dB sound pressure level. A1 and A2 have almost equal thresholds in contrast to noctuids and geometrids. A3 responds at + 12 to + 16 dB relative to the A1 threshold. The threshold data from the A-cells give no indication of frequency discrimination in greater wax moths. Tethered greater wax moths respond to ultrasound with short-latency cessation of ¯ight at + 20 to + 25 dB relative to the A1 threshold. The behavioural threshold curve parallels the audiogram, thus further corroborating the lack of frequency discrimination. Hence, the distinction between bats and conspeci®cs is probably based on temporal cues. At a constant duty cycle (percentage of time where sound is on) the pulse repetition rate has no effect on the threshold for ¯ight cessation, but stimulus duration affects both sensory and behavioural thresholds. The maximum integration time is essentially the same: 45 ms for the A1-cell and 50±60 ms for the ¯ight cessation response. However, the slopes of the time-intensity trade-off functions are very different: ± 2.1 dB per doubling of sound duration for the A1-cell threshold, and ± 7.2 dB per doubling of sound duration for the behavioural threshold. The signi®cance of the results for sexual acoustic communication as well as for bat defence is discussed.
Physiological Entomology, 2000, Vol 25, p. 354-362