DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS FROM THE TYMPANIC ORGAN IN 2NOCTUOID MOTHS

Distortion-product otoacoustic emissions were measured from the tympan ic organ of Ascalapha odorata (Noctuidae, Erebinae) and Empyreuma affi nis (=pugione) (Arctiidae, Ctenuchinae) during stimulation with two pu re tones of different frequency (f1,f2) within a frequency range betwe en 5 and 60 kHz. The cubic distortion-product that appears at a freque ncy of 2f1-f2 showed the largest amplitude and could be used to obtain ''distortion audiograms''. In such audiograms, the maximal distortion -product otoacoustic emission levels were measured for stimulus freque ncies that correspond to lowest Al-cell thresholds in each of the two species. Newly emerged E. affinis showed very low levels of the 2f1-f2 distortion, most of which were within the noise range. In contrast to vertebrate distortion-product otoacoustic emissions, in neither of th e species could an optimum f2/f1 ratio be easily defined, and small ra tios were sufficient to induce the distortions. We conclude that the e ars of the two moth species exhibit distinctly non-linear mechanical p roperties. Distortion-product otoacoustic emissions are a good non-inv asive method for studying the spectral response characteristics of the mechanics of their auditory organs, despite the fact that their morph ological characteristics are very different from those in vertebrates.