Behavioural context regulates dual function of ultrasonic hearing in lesser waxmoths: bat avoidance and pair formation

Abstract

Abstract. Ultrasonic hearing in moths evolved to detect bat echolocation cries and has been co‐opted into the mating system of some species. Some moths evade or approach ultrasonic stimuli that overlap in their spectral and temporal features. The present study addressed the evaluation of ultrasonic stimuli by lesser waxmoths, a species in which ultrasonic hearing functions in bat evasion and pair formation. Playback experiments show that the role of different stimulus features varies with behavioural context. Flying moths have a single evasive response, which is performed mainly on the basis of pulse length and stimulus power: they dive upon hearing loud pulses ≥ 1 ms in length, and respond more strongly to high‐power stimuli above that pulse length. Female moths walking on the ground respond with positive phonotaxis mainly on the basis of pulse rate by orienting toward pulses delivered at rates ≥ 30 pulses s−1. Consequently, moths on the ground approach stimuli that elicit evasion when detected in flight. However, the different responses given to stimulus features by flying and walking moths match the distinguishing features of bat cries and conspecific males in both contexts. Stimulus evaluation, modified by behavioural context, gives lesser waxmoths the flexibility to show appropriate evasion or approach responses to stimuli that overlap in their features.