Abstract. Considering the responses of both auditory receptors in Empyreuma pugione (Arctiidae, Ctenuchinae), it was found that this auditory organ maintains its frequency tuning and directionality over an intensity range of more than 60 dB. For the first time in the Lepidoptera we demonstrate a close frequency match between auditory sensitivity and the power spectrum of the sound emitted by the same species.Key words'. Moth audition; moth sound emission; Arctiidae; Ctenuchinae; sensory coding.The tympanic organ of Noctuoidea has two auditory receptor cells I 4, except in the Notodontidae, in which it has only one 5. Most existing data on the spectral characteristics of the two-celled auditory organs refer only to the most sensitive A1 cell 6 14; only three papers ~5 ~v deal with both receptors, A1 and A2 cells. All the above-mentioned results were obtained at threshold intensities; only Boyan and Fullard 1~ showed a suprathreshold Al-cell response curve at 70 dB SPL up to 30 kHz in Heliothis virescens (Noctuidae). In reports of directional responses only the Al-cell threshold responses of some Noctuidae were considered ~9.2~ Roeder 2~ states that the directionality characteristics of the Arctiidae are unknown. When considering the possible behavioral role of audition in moths, it should be kept in mind that in preypredator (moth-bat) relationships the speed of reaction is the most important feature, thus the information coding of stimulus characteristics such as frequency and position is not that important at high intensities (close range), when erratic maneuvers become decisive for the moth in evading the rapidly-approaching insectivorous bat 22. On the other hand, in intraspecific relations, the information coding of these same stimulus features becomes of paramount importance at close range, when intensity is high, for locating the conspecific insect precisely. In this study we describe the frequency response and directional sensitivity of the A1 and A2 cells at threshold and suprathreshold intensities in the noctuoid Empyreuma pugione (L.) (Arctiidae, Ctenuchinae). We also describe some characteristics of the sound pulses emitted by its microtymbalic organ, and demonstrate for the first time in the Lepidoptera a close frequency match between auditory sensitivity and the power spectrum of the sound emitted in the same species.
Material and methodsMoths of both sexes were collected in the field as imagines or as larvae, which hatched in the laboratory (for details of the rearing method, see Coroa3). For the electrophysiological recordings we mounted the animal ventral side up, as described by Roeder a4. E. pugione adopts this position naturally in the field, while perching on the lower surfaces of the leaves of Nerium oleander and plants, and also during copulation and oviposition. Spike activity of the auditory receptors was recorded with a stainless steel hook electrode from the tympanic nerve at the position where it joins the alar nerve in the mesothorax. Nerve activity was amplified, filtered (200 Hz high...
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