Auditory mate or prey localisation is central to the lifestyle of many animals and requires precise directional hearing. In insects where the body is small compared to the sound wavelength the directional performance of auditory systems is limited due to the lack of diffraction and minute interaural time differences. Some insects, however, possess specialised microscale hearing systems with astonishing functional properties.
Recent experiments by a team from the Department have demonstrated directional hyperacuity of the hearing system in the Mediterranean field cricket Gryllus bimaculatus. Dr Stefan Schöneich and Dr Berthold Hedwig analysed the precision of acoustic orientation in female crickets walking on a highly sensitive trackball system by measuring their steering accuracy towards male calling song. The females reliably discriminated the side of acoustic stimulation, even when the sound source deviated by only 1° from the animal's length axis. Moreover, for angles of sound incidence between 1° and 6° the females precisely walked towards the sound source.
Measuring the tympanic membrane oscillations of the front leg ears with a laservibrometer revealed between 0° and 30° a linear increasing function of interaural amplitude differences with a slope of 0.4 dB/°. Auditory nerve recordings closely reflected these bilateral differences in afferent response latency and intensity that provide the physiological basis for precise auditory steering.
The data reveal the acoustic orientation of field crickets as one of the most precise among invertebrates and place it at the same level to the achievements of vertebrate directional hearing. The work was supported by The Royal Society