Acoustic communication and orientation in grasshoppers

Phonotactic orientation of Chorthippus biguttulus, a behaviourally well studied acri-did species, serves as an example to outline the function, capacities and limitations of the grasshopper’s auditory performance. Results of behavioural, electrophysiological and anatomical studies are combined to reveal the neural pathway of acoustic information processing, and the mechanisms involved in acoustical communication and orientation. In Chorthippus, both males and females stridulate. The male approaches the female in small, distinct steps, each being associated with a turn towards the side from which the sound arrives, thus bringing the sound source to a lateral position on the opposite side. This lateralization behaviour is based on the interaural intensity difference. For species-specific signal recognition and for sex dis crimination, the acoustic inputs from both sides are summed, whereas directional information is processed in parallel on either side via separate channels ascending to the brain. Although in both the task of signal recognition and the task of sound localization a substantial part of information processing occurs in the first stage of synaptic interactions in the metathoracical ganglion (TG3), the final step of song recognition, as well the final decision on the direction of turning, take place in the brain.