Ultra high frequency hearing in a moth
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1
University of Strathclyde, Department of Electronic and Electrical Engineering, United Kingdom
The function of the moth tympanal hearing organ is understood reasonably well. Hearing in moths is primarily for the detection of predating bats, which is one of the best known evolutionary arms-races between predator and prey. However, many moth species have exploited this evolution of the hearing sense for another purpose; intra-specific communication. Using adapted body parts on various body regions, depending on the species, these moths can communicate. The hearing organs of such moths have adapted to include these sounds in their hearing range. One example is the greater wax moth (Galleria mellonella), of the family Pyralidae. Male wax moths produce sound with structures known as tymbals located on the forewing attachment. Sound is produced as the wings are beaten; a train of ultrasonic pulses being produced due to the tymbal buckling, so producing trains of pulses; the sound attracts females to mate. The sound pulse intrinsic frequencies are 70-90 kHz. The wax moths also detect bats, with a known sensitivity to calls in the range 20-120 kHz. The wax moth tympanal hearing organ is relatively simplistic with four auditory mechanoreceptor cells attaching to the membrane. The mechanoreceptors require a minimum displacement in order to elicit an action potential. Previous studies have suggested that the hearing extends higher into the ultrasonic range. However, this is suggested only on the basis of behavioural experiments. Here, we report experiments to investigate the ultrasonic frequency capability of the G. mellonella hearing organ using an air-coupled ultrasonic transducer to produce ultrasound up to 300 kHz. The tympanal membrane vibrations were investigated using laser Doppler vibrometry, recording scans of the membrane surface displacements. The response of the auditory nerve was recorded using extracellular electrophysiology. The results show that there are still relevant displacements of the tympanal membrane up to 300 kHz; electrophysiology recordings also confirmed that there were auditory nerve responses up to 300 kHz. The minimum sound levels needed to elicit a nerve response at these high frequencies were relatively low, around 80 dB SPL; this increased to around 90 dB SPL at 300 kHz. Thus, the combination of mechanical and electrophysiological measurement indicates that the moth G. mellonella can hear frequencies up to 300 kHz. We believe this is the highest recorded frequency sensitivity in any animal. There may be a number of reasons that the moths have evolved the need for this ultra-high frequency hearing. Some species of bats have been found to echolocate at very high frequencies (>200 kHz). This result may indicate that the moths have adapted to the bat’s use of such high frequency ultrasound. It may also be that the wax moth hearing organ functions as a basic switch, taking a minimum displacement of the membrane to produce a nerve response. Therefore, the moth ear acts as a very broadband receiver, triggering a response at any frequency, given enough sound energy. This is supported by behavioural studies indicating that the moths respond to these high frequencies with the same bat evasion behaviour seen from lower frequencies.
Keywords:
bioacoustics,
Insect hearing
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Sensory: Audition
Citation:
Moir
H,
Jackson
J and
Windmill
J
(2012). Ultra high frequency hearing in a moth.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00125
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Received:
26 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Miss. Hannah Moir, University of Strathclyde, Department of Electronic and Electrical Engineering, Glasgow, United Kingdom, hannah.moir@eee.strath.ac.uk