1997, 569, Session T3, Poster

Near-field sound reception by particle displacement receptors on the cerci of the praying mantis, Sphodromantis aurea

*J.D. Triblehorn, D.D. Yager (University of Maryland at College Park, College Park, Maryland)

The praying mantis (Sphodromantis aurea) has filiform hairs located on two posterior appendages (the cerci) which are sensitive to particle displacement. Particle displacement is the component of sound which dominates in the area close to a sound source, known as the near-field. The sensitivity and response characteristics of these receptors were compared to those of the male cockroach (Periplaneta americana) which is closely related to the praying mantis and in which the particle displacement receptors are well-studied. Physiological recordings from the cercal nerve were used to determine thresholds of particle displacement produced by sound ranging from 30-2500 Hz. Due to the very high sensitivity of these receptors, particle displacement was determined indirectly from pressure measurements. The results show that male and female mantises and male cockroaches have similar sensitivities to near-field sound. The best frequency region is at 100-400 Hz. Sensitivity to particle displacement decreases sharply below 100 Hz and gradually above 400 Hz, but still remains relatively sensitive over 1000 Hz. As sound frequencies decrease, the boundary layer (an area where there is no particle displacement) created on the surface of the cerci gets larger. The sharper decrease on the lower frequency end could result from the absence in both mantises and cockroaches of filiform hairs that are taller than the boundary layer. Therefore, sensitivity at these low frequencies decreases sharply. The cercal nerve recordings also show phase locking to the sound stimulus that was similar in male and female mantises and male cockroaches, occurring at 30-300 Hz. Phase locking begins to break down at 400 Hz, and at higher frequencies the cercal nerve shows primarily onset and offset responses to the stimulus. Although the function of the near-field auditory system of the praying mantis is not yet known, in other insects, it is important in intraspecific communication (especially sexual selection), detection of ground predators, and detection of air-borne predators.

Supported by NIDCD Training Grant T32 DC-00046 to JDT