Behavioral response to ultrasound by the tiger beetle Cicindela marutha dow combines aerodynamic changes and sound production

Abstract

Tethered flying tiger beetles, Cicindela marutha, respond to trains of bat-like ultrasonic pulses with a short-latency, multi-component behavior. The head rolls to one side, the metathoracic legs kick to the opposite side, the elytra swing backwards towards the hindwings and pronate, the hindwings increase their stroke excursion and frequency, and the plane of the hindwing motion tilts forward. In addition, the beetles produce trains of ultrasonic clicks typically containing 100-200 clicks in response to a 1 s stimulus. The clicks average 85-90dB SPL at 2 cm. The latencies for hindwing changes and elytra swing in response to stimuli more than 10dB over threshold are 90-110 ms; the latency to clicking is 120-150ms. Neither the head roll nor the leg kick appears to be directional relative to the sound source. The behavioral response is broadly tuned with greatest sensitivity at 30-60 kHz and mean behavioral thresholds of 75-80 dB SPL. Physiological audiograms from the auditory afferents show substantially greater sensitivity and sharper tuning than the behavioral response, which suggests that tiger beetles may use their hearing in other contexts as well as during flight. The combination of aerodynamic components and arctiid-moth-like clicking may provide these insects with a powerful defense against attack by echolocating bats.