AUDITORY PERCEPTION IN MALE MOSQUITOES (DIPTERA, CHIRONOMIDAE)
DURING FLIGHT SIMULATION
As a part of mating behavior male mosquitoes detect and locate females by the sound
generated by their wingbeats. Up to date the auditory physiological properties
in mosquitoes were studied in a steady preparation. However, sensory organs of
a flying insect are affected by a strong vibration induced by the wings
and flight muscles. This effect can sufficiently modify the perception since
receptor cells possess non-linear characteristics. The aim of this study was
to demonstrate the effect of flight conditions on the functioning of the
Johnston's organs (hearing organs) in male Chironomus plumosus L.
To simulate the flight conditions around the mosquito a small amount of air was shifted at 400 Hz along the dorso-ventral axis. These air oscillations carried the mosquito feather-like antennae causing vibrations of the antennal flagellum that are transmitted to and sensed by Johnston's organ. Along with the flight simulation the mosquitoes were stimulated by a low-amplitude sinusoidal auditory signals of different frequencies. The responses were recorded from Johnston's organ neurons using glass microelectrode.
Auditory responses contained two rhythms of amplitude modulation which were produced due to non-linear processes in receptors: the first rhythm had the difference frequency of flight simulation and the stimulus; the second rhythm corresponded to the beating of heterodyne frequencies. Compared to the steady-state conditions the additional optimum of auditory sensitivity was found at 440-600 Hz (so-called image channel) during flight simulation. The second harmonic of conspecific female sound corresponds to this optimum. Also the improvement of sensitivity by 7 dB (2.2-fold) was observed at the main optimum (200 - 320 Hz).
We conclude that mechanical influence caused by locomotor movements not only adds noise to the sensory system but also can improve its sensitivity or add new properties.