MOSQUITO BIOACOUSTICS: AUDITORY PROCESSING IN MALES OF CULEX PIPIENS PIPIENS L. (DIPTERA, CULICIDAE) DURING FLIGHT SIMULATION
As a part of mating behavior, male mosquitoes detect and locate
a female by listening to the sound accompanying its 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 flight
muscles and the wings. This influence 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
Culex pipiens pipiens L.
To simulate the flight conditions around the mosquito a small amount of air was shifted at 500 Hz along the dorso-ventral axis. These air oscillations carried the mosquito feather-like antennae, causing the vibration of the antennal flagellum which, in its turn, was transmitted to and sensed by the Johnston's organ. Along with the flight simulation the mosquito was stimulated by a low-amplitude sinusoidal auditory signals of different frequencies. The responses were recorded from 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 540-640 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 (220 - 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 even add new properties.