Noctuid moth echolocation

Temporal resolution of a moth ear

The principal possibility to realize echolocator requires sufficient temporal resolution of an ear - it must be able to distinguish between the own probing signal and the echo that follows shortly.

Compared to other echolocating animals, noctuid moths are very small - their common wingspan is about 2.5 - 3cm. For adequate orientation a moth must be able to detect echoes from a commensurable distance (say, 3 - 20 cm) which gives us delays from 0.18 to 1.2 ms according to the speed of sound. Detection of obstacles at greater distances is also could be possible, but location within the immediate surroundings is of fundamental importance since it is intended to prevent sudden collisions.

Theoretically estaimated temporal resolution of the tympanic membrane, based on different assumptions, lies within the range 0.18 - 0.35 ms (Lapshin, Fyodorova, 1996), which means that the membtane itself allows to distinguish between the two sounds coming shortly one after another.

But, several independent studies had demonstrated that the most sensitive acoustic receptor, the A1 cell, is capable to distinguish two pulses with no less than 3ms between them (Lapshin, Fyodorova, 1996; Tougaard, 1996).

Thus, the echolocation in noctuid moths is possible only provided that auditory receptors do not respond to the probing click. Otherwise an echo will return to the ear at the moment of spike generation in response to the probing click or within the cell refractory time. We have a good reason to beleive that the own probing clicks of a moth cause a paradoxical response in auditory receptors - the suppressing of their activity for a certain period of time. It should be noted that the decrease of response to a loud signals was demonstrated in different animals, including moths (Perez, Coro, 1985).

Using the retransmission method, we have managed to test moths for the ability to detect echoes coming very shortly after their own probing clicks. Adjusting the delay between the probing click produced by a moth and an artificially generated echo-stimulus we have measured the auditory thresholds in two noctuid species, Enargia paleacea and Blepharita satura (Lapshin, Vorontsov, 2003, 2009).

Our findings reveal the ability of noctuid moths to perceive echoes of their own signals, which means that temporal resolution of their ears does not prevent them from using short-range echolocation.

References

Lapshin D.N., Fyodorova M.V. (1996) Responses of noctuid tympanal organs (Noctuidae: Amphipyra perflua) to the impulse ultrasound signals // Sensornye Systemy, 1996. V.10. ¹1. P.5-17 (in Russian). Translation: Responses of the tympanic organs of cutworm moth (Amphipyra perflua : Noctuidae) to ultrasound impulses // Sensory Systems. V.10. ¹1. P.1-11.

Tougaard J. (1996) Energy detection and temporal integration in the noctuid A1 auditory receptor // J. Comp. Physiol. V.178. ¹5. P.669-677.

Perez Ì., Coro F. (1985) Physiological characteristics of the tympanic organ in noctuoid moths // J. Comp. Physiol. V.156. P.689-696.

Lapshin D.N., Vorontsov D.D. (2003) Sensitivity of the noctuid moth Enargia paleacea Esp. (Lepidoptera, Noctuidae) to echo-like stimuli // Doklady Akademii Nauk, 2003, V.390. ¹4. P.565-567. Translation: Doklady Biological Sciences", 2003, V.390, ¹1/6, P.210-212.

Lapshin D.N., Vorontsov D.D. (2009) The dependence of behavioral auditory thresholds on the delay of echo-like signals in noctuid moths (Lepidoptera, Noctuidae) // Journal of Integrative Neuroscience, V.8. ¹1. P. 1-12.