D.N. LAPSHIN
DIRECTIONAL AND FREQUENCY CHARACTERISTICS OF AUDITORY RECEPTORS IN MIDGES (DIPTERA, CHIRONOMIDAE)
Individual characteristic frequencies and directional sensitivity of
the Johnston's organ auditory receptors were measured in the midges Chironomus
plumosus L. using the method of positive feedback stimulation: responses
of receptors recorded with a glass microelectrode from their axons in the
antennal nerve were amplified and fed to the stimulating speaker. With
the amplitude and the stimulating signal phase properly adjusted, the
whole feedback loop fell into auto-excitation with the frequency of
oscillations close to the characteristic frequency of the receptor. Three
separate groups of receptors were found with mean frequencies of 180, 221,
and 264 Hz. These groups differ in their directional properties: the
low-frequency receptors are mostly sensitive dorsoventrally, while the
directional maxima of mid- and high-frequency ones are combined to provide
equal sensitivity in the plane perpendicular to the flagellum. Our data
suggest that in Chironomidae a single Johnston's organ together with
the antenna can provide spatial localization of conspecific sounds and also
perform the initial stages of frequency analysis.