Physiological characteristics of the tympanic organ in noctuoid moths

Summary

• 1. The tympanic organs ofSpodoptera frugiperda, Mocis latipes, Erebus odorata, Maenas jussiae andEmpyreuma pugione (Lepidoptera) were stimulated with acoustic pulses of 3.5 ms duration, 20 kHz intrinsic frequency and intensities ranging from 35 to 100 dB (0 dB=2×10⁻⁵ N/m²). The electric activity of the auditory receptors was recorded with a stainless steel hook electrode at the tympanic nervelet, in the zone where it adjoins the alar nerve in the mesothorax.

• 2. The increase of stimulus intensity above threshold evokes a linear increment in the number of spikes per acoustic pulse of the auditory receptors (A₁ and A₂ cells), without saturation even with the highest intensities used. At the same time the latency period of the response of both auditory receptors decreases exponentially. The interspike intervals during the response of these cells change with stimulus intensity, as well as with the time-course of the response.M. latipes shows the briefest interval value, around 1.0 ms, whileE. pugione has the longest, around 1.8 ms.S. frugiperda andM. latipes show brief latency periods (less than 2.0 ms for intensities 20 dB above the A₁-cell threshold), and during the response the briefest interval occurs sooner than in the other three species, which show longer latency periods (around 3.0 ms); the minimum interspike interval value is reached later.

• 3. These interspecific differences may be due to the temporal course of the generator potential of the auditory receptors.