  We investigate the role of the noise in the mating behavior between
individuals of Nezara viridula (L.), by analyzing the temporal and spectral
features of the non-pulsed type female calling song emitted by single
individuals. We have measured the threshold level for the signal detection, by
performing experiments with the calling signal at different intensities and
analyzing the insect response by directionality tests performed on a group of
male individuals. By using a sub-threshold signal and an acoustic Gaussian
noise source, we have investigated the insect response for different levels of
noise, finding behavioral activation for suitable noise intensities. In
particular, the percentage of insects which react to the sub-threshold signal,
shows a non-monotonic behavior, characterized by the presence of a maximum, for
increasing levels of the noise intensity. This constructive interplay between
external noise and calling signal is the signature of the non-dynamical
stochastic resonance phenomenon. Finally, we describe the behavioral activation
statistics by a soft threshold model which shows stochastic resonance. We find
that the maximum of the ensemble average of the input-output cross-correlation
occurs at a value of the noise intensity very close to that for which the
behavioral response has a maximum.
