Hearing and evasive behaviour in the greater wax moth, Galleria mellonella(Pyralidae)

Greater wax moths (Galleria mellonella L., Pyraloidea) use ultrasound sensi tive ears to detect clicking conspecifics and echolocating bats. Pyralid ea rs have four sensory cells, A(1-4). The audiogram of G. mellonella has best frequency at 60 kHz with a threshold around 47 dB sound pressure level. A( 1) and A(2) have almost equal thresholds in contrast to noctuids and geomet rids. A(3) responds at + 12 to + 16 dB relative to the A(1) threshold. The threshold data from the A-cells give no indication of frequency discriminat ion in greater wax moths. Tethered greater wax moths respond to ultrasound with short-latency cessati on of flight at + 20 to + 25 dB relative to the A(1) threshold. The behavio ural threshold curve parallels the audiogram, thus further corroborating th e lack of frequency discrimination. Hence, the distinction between bats and conspecifics is probably based on temporal cues. At a constant duty cycle (percentage of time where sound is on) the pulse r epetition rate has no effect on the threshold for flight cessation, but sti mulus duration affects both sensory and behavioural thresholds. The maximum integration time is essentially the same: 45 ms for the A(1)-ce ll and 50-60 ms for the flight cessation response. However, the slopes of t he time-intensity trade-off functions are very different: - 2.1 dB per doub ling of sound duration for the A(1)-cell threshold, and - 7.2 dB per doubli ng of sound duration for the behavioural threshold. The significance of the results for sexual acoustic communication as well a s for bat defence is discussed.