Phonotaxis inGryllus campestris L. (Orthoptera, Gryllidae)

Summary

Phonotaxis of receptive female field crickets (Gryllus campestris L.) towards a taped model of the species-specific calling song (Fig. 1) presented azimuthally at 12 different sound pressure levels, ranging from 39 to 106.5 dB, is investigated using a locomotion compensator. The orientational performance of the crickets is analysed in the intact state (1.), as well as after occlusion of both prothoracic spiracles (2.), both posterior tympana (3.), both prothoracic spiracles and both posterior tympana (4.), one posterior tympanum and one prothoracic spiracle at a time (5.).

• 1. In intact female crickets acoustic orientation on average starts at 44 dB. The orientational performance improves steadily up to 79.5 dB, deteriorates slightly at 86 and 91.5 dB and remarkably at 106.5 dB calling song intensity (Figs. 3, 4 and 11).

• 2. Following wax occlusion of both prothoracic spiracles (Figs. 5 and 6) behavioural threshold of phonotaxis is raised by on average 5 dB to 49 dB. The course of the intensity curve is similar to that evaluated for intact crickets, the orientational performance at a given intensity being merely slightly reduced (Fig. 11).

• 3. Occlusion of both posterior tympana (Figs. 7 and 8) does not abolish the capability of acoustic orientation. Compared to intact animals the behavioural threshold is only raised by on average 17.5 dB to 61.5 dB (Fig. 11). Orientational performance at suprathreshold intensities improves with increasing song intensity, but remains inferior to that of intact crickets unless a 106.5 dB calling song is presented.

• 4. Phonotaxis is even evident after occlusion of the posterior tympana and the prothoracic spiracles with wax (Figs. 9 and 10). This operation results in an effective attenuation of on average 30 dB, the behavioural threshold being raised to 74 dB (Fig. 11). At suprathreshold intensities orientational performance is further reduced compared to that of crickets after occlusion of the posterior tympana only.

• 5. Occlusion of a posterior tympanum and a prothoracic spiracle on opposite sides results in a stable course deviation of on average 49 ° towards the side of the intact posterior tympanum at 61.5 to 91.5 dB (Figs. 13, 14A and B). This demonstrates that the effect of an occluded posterior tympanum overrides that of an occluded prothoracic spiracle. Occlusion of these sound entrances on the same side results in strong turning tendencies towards the intact side, which increase with calling song intensity (Fig. 14C and D). Except in a single cricket's run performed at 106.5 dB, stable courses are no longer found (Fig. 15). Thus, phonotaxis is more strongly impaired than after occlusion of these sound entrances on opposite sides.