Generation and radiation of sound by stribulating water insects as exemplified by the corixids

Summary

• 1. The sound-pressure pulses emitted under water by stridulating corixids have decay envelopes typical of an approximately exponentially damped oscillatory system (Fig. 1). Loud pulses are more strongly damped than soft pulses. The logarithmic decrement Λ is between 1.0 and 0.4 (Fig. 8).

• 2. The Fourier spectra of these pulses have a pronounced, relatively narrow-band peak (Fig. 7). The apex of the peak (fundamental frequency) for male Corixa dentipes and C. punctata lies within a frequency band of about 1.5–2.8 kHz.

• 3. The volume of the bubble of respiratory air in and on the body of submerged animals varies between ca. 10 and 45 mm³ in C. dentipes. The natural frequencies of spherical air bubbles of the same volume in water are 2.5–1.5 kHz.

• 4. During a diving phase the fundamental frequency of the stridulatory sounds changes in accordance with the change in volume of the individual's air bubble (Figs. 3-5).

• 5. Thus Corixa generates underwater sound by means of the transient volume pulsations induced in the air bubble, at its natural frequency, by stridulation. It appears that this principle may be generally valid for stridulating water insects bearing air bubbles (Fig. 10).

• 6. The stridulatory sounds of one animal induce resonant oscillation in the air bubbles of a nearby animal, such that it in turn becomes a sound radiator (Fig. 9). The significance of the bubble of respiratory air in corixid auditory communication is discussed.