Reception of medium vibration by thoracal hairs of caterpillars ofBarathra brassicae L. (Lepidoptera, Noctuidae)
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- Tautz, J. J. Comp. Physiol. (1978) 125: 67. doi:10.1007/BF00656832
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A single sensory cell innervates each of the 8 filiform hairs on the thorax ofBarathra brassicae caterpillars.
It is not spontaneously active nor does it respond to a maintained deflection of the cuticular hair. It responds to changes in hair position away from or back to resting position in a purely phasic fashion (Fig. 1).
At a constant duration of hair motion for reaching the final deflection the number of occurring impulses (y) depends on hair-deviation-angle (x) according to the power functiony=6.76·x°0.38.
The impulse rate (y) drops with time (t) after onset of step stimuli according toy = 1174.9·t−0.67 (Fig. 3).
If one plots the first interpulse interval against angular velocity of hair motion a sigmoid shaped response curve results with its steepest slope in the range 50-100°/s (Fig. 6).
The directional characteristic of the sensory cell shows a cadioid-like profile of sensitivity (Fig. 15) with its sensitivity maximum for deflections in the direction where the dendrite inserts at the hair base.
The threshold of impulse initiation by sine stimulation drops from 2.5° hair deflection from resting position at 40 Hz to 0.5° deflection at 150 Hz and than stays at a nearly constant level up to 1000 Hz. The response breaks abruptly off around 1000 Hz (Fig. 9). Bristles on the thoracic segments show a minimum threshold curve with a sensitivity maximum of 0.3° at 150 Hz (Fig. 10).
At sine stimulation the sensory cell of the filiform hairs adapts only slowly. At a stimulus frequency of 100 Hz the response begins to decrease after 5 s and vanishes after ca. 20 s.
The impulses occur at a constant phase of the sine wave at a given stimulus frequency. At frequenciesf< 40 Hz every half sine wave is responded to, at frequenciesf≳= 40 Hz the response occurs only at hair motion to the ventral side. In the frequency range 40 Hz ≦f≦ 200 Hz every sine wave is responded to by one impulse.
Response to sine wave onset with different rise-time has an initial phasic or “quasi-phasic” peak of discharge rate (Fig. 13).
The medium vibration in the near-field of a flying wasp is an adequate stimulus for the filiform hair. A flying wasp can stimulate the sensory cell from a distance of maximally 70 cm.