Sound production by abdominal tymbal organs in two moth species: The greensilver-line and the scarce silver-line (Noctuoidea : Nolidae : Chloephorinae)

Male moths of the chloephorine species Pseudoips prasinana and Bena bicolor ana produce clicks (approximately 100 dB peSPL at 10cm) using ventral tymba l organs located in a cleft in the second abdominal sternite. Large muscles insert on the dorsal part of the tymbal frame and rhythmically flex a thin sheet of cuticle. Normally, each sound-production cycle contains four clic ks, the left and right tymbals producing clicks both on active buckling cau sed by muscle contraction and on the passive elastic return from buckling. Histochemical staining indicated the presence of elastic resilin-like prote ins in the tymbals, Obvious differences between the click patterns of the t wo species reflect differences in their tymbal morphology. P. prasinana has smooth tymbals and produces a single click (300 mu s, 40kHz) for each tymb al buckling, In contrast, B. bicolorana has striae on the medial part of th e tymbals, Accordingly, it produces many clicks per buckling. The click pat tern is a heterogeneous mixture of large clicks at 52 kHz, resembling those of P. prasinana, interspersed with series of broad-band clicks (20-100 kHz ) of lower intensity (15-20 dB), Thus, in chloephorine moths, there is a co rrelation between the structure and function of the smooth and striated tym bals that is strikingly similar to that in arctiid moths, although the two types of tymbals have evolved independently, The hearing of P. prasinana is tuned to its own sounds with lowest threshold (38 dB SPL) at 40-60kHz. We suggest that sound production in male chloephorines plays a part in sexual acoustic communication.