Phonotaxis inGryllus campestris L. (Orthoptera, Gryllidae)

Summary

One of the four sound entrances (two posterior tympana and two prothoracic spiracles; Fig. 1) of the auditory system of female field crickets (Gryllus campestris L.) was occluded with wax.

• 1. After single occlusions and in the absence of external directional stimuli the crickets behave like intact unorientated animals: they do not walk in any consistent direction (Fig. 2). Walking velocity (Fig. 3) is not reduced in comparison with that of intact crickets. Systematic changes in angular velocity do not occur (Fig. 4, Table 1). Thus, unorientated walking is not affected by the occlusion of sound entrances.

• 2. With calling song presentation, occlusions of one sound entrance (tympanum or spiracle) result in course deviations to the intact side (Figs. 5–7). As in intact, acoustically orientating crickets, oscillations around the mean walking direction occur, accompanied by occasional full turns to the intact side (Figs. 5 and 7). The response mechanism underlying the acoustic orientation of operated crickets is described by the nearly sinusoidal characteristic of their corrective turns (characteristic curve; Fig. 7). After single occlusions, the characteristic curves are shifted by a constant angular velocity towards the intact side. The accuracy of course maintenance is reduced in comparison to that of the intact animals.

• 3. The functional role of a prothoracic spiracle in hearing is shown to be virtually the same as that of the ipsilateral posterior tympanum. From our behavioural results the question arises, whether tympanal membrane vibration is necessary for the excitation of the auditory sense cells inGryllus campestris. In addition, our results do not support an ipsilateral pressure-gradient mechanism for directional hearing in this species.