Range of corixid sound signals in the biotope

Abstract

ABSTRACT. The propagation of sound in the frequency band (2–12 kHz) used by the Corixidae was measured in two shallow natural ponds. At distances of more than 1 m from the shore the water was at least O.4 m deep. The first pond was eutrophic and contained no plants. The spread of sound into the open water obeyed approximately the geometric attenuation of the sound pressure level (SPL); a loss of 6dB for each doubling of the distance from the point sound source. Near the shore the attenuation was considerably greater, especially for low frequencies; for a 2 kHz signal the damping of the SPL was c. 40–50 dB/m.The second pond had dense plant growth, and the sound attenuation depended strongly on the photosynthetic activity of the waterplants. Measurements in winter, with an overcast sky, revealed only a slight damping effect of the plants for a 10kHz test signal. During intense sunlight in summer, however, in addition to the geometric attenuation the damping effect of the plants over a distance of O.5 m was 50 dB for a 2 kHz signal and 80 dB for 10 kHz. This effect was due to gas bubbles produced during intense photosynthesis.Song A of Corixa dentipes Thms. (Heteroptera) males elicits usually a response by male conspecifics. The threshold SPL for this response was measured to be c. 40 dB lower than the SPL at a distance of O.1 m from a stridulating animal. From the measurements of sound propagation it follows, therefore, that the effective range of Song A in the most favourable case is at least 10m, though in a pond overgrown with plants it can be less than O.4 m.