Functional poperties of viboreceptors in the legs ofNezara viridula (L.) (Heteroptera, Pentatomidae)

Abstract

1. Responses of the leg vibratory receptor neurons of the bugNezara viridula to substrate vibrations were recorded electrophysiologically and analysed. 2. The low frequency receptor neurons (LFR) respond in a phase-locked manner in the frequency range below 0.12 kHz. The low frequency receptor neurons of the first type (LFR 1) have been analysed in detail. Receptor neurons of this type respond to the upward movement of the leg in a vibration cycle. Their threshold curves follow the line of equal displacement values above 0.05 kHz of the stimulus carrier frequency (Fig. 1). Increasing displacement brings about an increase in the number of spikes per phase (Fig. 2). 3. The higher frequency vibratory receptor neurons are of two types. The middle frequency receptor neurons (MFR) show the highest sensitivity to the velocity component of vibration at frequencies around 0.2 kHz (Fig. 1); the high frequency receptor neurons (HFR) are most sensitive to velocity at frequencies between 0.75 and 1 kHz (Fig. 1). In the frequency range below the best velocity sensitivity, the threshold curves of both types of neurons follow the line of equal acceleration values; above the best frequency the curves follow the line of equal displacement values (Fig. 1). The shapes and positions of the response curves of both types depend on the stimulus carrier frequency (Fig. 3). The middle (MFR) and high frequency receptor neurons (HFR) respond with characteristically prolonged responses to applied vibrational stimuli of 0.2 kHz carrier frequency (Figs. 4–6). The phase-locked response pattern is observed in both neuron types in the frequency range up to 0.2 kHz (Figs. 4–6). 4. The frequency and time characteristics of the femaleNezara viridula calling song (FS 1) are well followed by the middle (MFR) and high frequency receptor neurons (HFR) (Figs. 7, 8), but the low frequency receptor neurons (LFR) follow the lower frequency components of the same female sound emission only at higher displacement values. 5. The origins of the responses of the low (LFR), middle (MFR) and high frequency receptor neurons (HFR) are discussed. The special response characteristics of the higher frequency receptor neurons, i.e. the middle (MFR) and high frequency (HFR) receptor neurons, at 0.2 kHz stimulus frequency may be due to the resonance of the special flaglike structure of cap cells of the subgenual organ.