Transmission of Podisus maculiventris tremulatory signals through plants

Males of the predaceous stink bug Podisus maculiventris (Say) (Heteroptera: Pentatomidae: Asopinae) emit low frequency tremulatory signals. Laser vibrometry was used to record and analyze naturally emitted signals, focusing on variation in signal velocity and frequency during transmission through plants (Phaseolus vulgaris L. and Plumbago auriculata Lam.) as a function of distance from the vibrational source. Signal velocity varied individually between 2 and 15 mm/s recorded on a plant close to the calling male and decreased by 0.3 to 1.5 dB/cm on bean and 0.3 to 0.9 dB/cm on plumbago. The dominant frequency of signals was variable at frequencies below 50 Hz. On bean frequencies centered around 10 Hz or 20 Hz were dominant for signals recorded at the source. Transmission through bean resulted in an increase in the 20 Hz peak relative to other frequencies in the signal. Variation of the dominant frequencies of signals transmitted through plumbago stems were more predictable, showing typical changes in amplitude relative to the distance from the source. The regular variation of the dominant frequency along the stem with linear increase of signal velocity at decreasing distance from the source may provide plant-dwelling insects with information about the distance to the calling individual.