Acoustic orientation via sequential comparison in an ultrasonic moth.

Orientation of female lesser wax moths (Achroia grisella) to male calling song was tested on a locomotion-compensator device that withheld all inter-aural acoustic differences from the insect. Under these circumstances, females remained longer in the vicinity of the sound source if they experienced a variable sound level that increased when approaching the source rather than a level that remained constant at all times. Analyses of orientation paths revealed that greater retention near the source was achieved by enhanced turning when the perceived sound level remained unchanged or decreased but retaining the previous heading when the level increased. These findings suggest that acoustic orientation can be supplemented by mechanisms based on sequential, as opposed to instantaneous, comparison of auditory input. Such mechanisms may be valuable when binaural hearing is impaired or asymmetric or in environments where acoustic differences at the two ears are unreliable indications of direction to the sound source.