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Abstract
Sexual recognition through wing-beat frequency matching was first demonstrated in
Toxorhynchites brevipalpis, where wing-beat frequencies of males and females are similar.
Here we show frequency matching in Culex quinquefasciatus, where the wing-beat frequencies
of males and females differ considerably. The wing-beat frequencies converge not on
the fundamental but on the nearest shared harmonic (usually female's third and male's
second). Frequencies in this range are, however, too high to elicit phasic sensory-neural
responses from the Johnston's organ (JO) or to drive the mosquito's motor neurons.
Potential cues for frequency matching are difference tones produced by nonlinear mixing
of male and female flight tones in the vibrations of the mosquito's antennae. Receptor
potentials and neural-motor activity were recorded in response to difference tones
produced when a mosquito was stimulated simultaneously by two tones at frequencies
outside the phasic response range of the JO but within range of the antennal vibrations.
We demonstrate sexual recognition through matching of flight-tone harmonics in Culex
mosquitoes and suggest that difference tones are used as an error signal for frequency
matching beyond the frequency range of the JO's sensory-neural range. This is the
first report of acoustic distortion being exploited as a sensory cue, rather than
existing as an epiphenomenon.