On the spot: utilization of directional cues in vibrational communication of a stink bug

Although vibrational signalling is among the most ancient and common forms of communication, many fundamental aspects of this communication channel are still poorly understood. Here, we studied mechanisms underlying orientation towards the source of vibrational signals in the stink bug Nezara viridula (Hemiptera, Pentatomidae), where female vibrational song enables male to locate her on the bean plant. At the junction between the main stem and the leaf stalks, male placed his legs on different sides of the branching and orientation at the branching point was not random. Analyses of signal transmission revealed that only a time delay between the arrival of vibrational wave to receptors located in the legs stretched across the branching was a reliable directional cue underlying orientation, since, unexpectedly, the signal amplitude at the branching point was often higher on the stalk away from the female. The plant and the position of the vibrational source on the plant were the most important factors influencing the unpredictability of the amplitude cue. Determined time delays as short as 0.5 ms resulted in marked changes in interneuron activity and the decision model suggests that the behavioural threshold is in the range between 0.3 and 0.5 ms.