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.