First recording of the sound produced by the black citrus aphid, Toxoptera aurantii (Boy.)

The black citrus aphid, Toxaptera aurantii (Boy.), produces a distinct scraping sound by rhythmic movements of whole colonies. It is the only species of aphid known to produce audible sounds and the acoustical content of a preliminary recording of these sounds is reported in detail. During one recording the aphids stridulated 15 times in 21 seconds, giving an average period of 1–4 seconds between emissions and this rate remained virtually constant for at least an hour. Analysis of the recording established a clear peak frequency band at about 4–6 kHz with another around 800 Hz-1 kHz and possibly another in the ultra-sonic range above 18 kHz. Morphological adaptations of the abdominal cuticle and of the hind tibiae to form a stridulatory apparatus are illustrated and possible functions of stridulation as a defence mechanism or as a means of intraspecific communication are briefly discussed.