Sound production by hawkmoth larvae and pupae through abdominal spiracles

Some insect species produce defensive sounds across developmental stages. To test whether the characteristics, organs and mechanisms of sound production differ across stages within a single species, we examined how larvae and pupae of Phyllosphingia dissimilis (Lepidoptera: Sphingidae) produce sounds in response to simulated predator attacks via tactile stimulation. Laboratory experiments showed that final-instar larvae produce sound pulses (dominant frequency: 9.2-12.9 kHz; sound pressure level: 50.2-62.4 dB SPL) by expelling air through the pair of eighth abdominal (A8) spiracles, whereas pupae can produce sound pulses (3.8-21.6 kHz; 42.0-53.5 dB SPL) by forcing air through any of the spiracle pairs on the second to seventh abdominal segments (A2-A7). Despite differences in spiracle involvement, both stages employ a similar air-forcing mechanism. While the larval mechanism is known from other hawkmoth species, this is the first report of sound production via airflow through abdominal spiracles in insect pupae.