Effects of heterospecific and conspecific vibrational signal overlap and signal-to-noise ratio on male responsiveness inNezara viridula(L.)

Animals often communicate in environments with high levels of biotic noise that arises from the signals of other individuals. Although effects of background biotic noise on mate recognition and discrimination have been widely studied in air-born sound communication, little is known about incidental interference between signallers that use substrate-borne vibrational signals. In this study we investigated the ability of males of the southern green stink bug Nezara viridula (L.) (Heteroptera: Pentatomidae) to recognize conspecific female song in the presence of biotic noise originating from conspecific and heterospecific vibrational signals. We tested male responsiveness on a bean plant in playback experiments. One leaf was vibrated with conspecific female song, while to the other one we simultaneously applied either heterospecific female signal or various altered conspecific signals with different temporal parameters. We tested males in three levels of biotic noise, ranging from +6 dB to -6 dB and we compared male responsiveness in each treatment with response obtained in unilateral treatment with unaltered conspecific female calling song. Male responsiveness was reduced in the presence of heterospecific signals or when background noise from conspecific signals obscured the species-specific temporal pattern of conspecific female song. By contrast, the presence of two sources of conspecific female songs had a positive effect on male responsiveness, for as long as the signal repetition rate of perceived song did not differ from the species-specific value. In the presence of interfering background signals, searching activity was less affected than male signalling. Increased signal-to-noise ratio restored male responsiveness to the level expressed in unilateral stimulation with conspecific female song. The results are discussed with regard to male behavioural strategies for vibrational communication in a noisy environment.