1975] 
Willey — Sound Production in Arphia 
333 
Because the femora often are out of phase and modulate one 
another, one can not merely count spikes of sound and numbers of 
pegs on the calculated route of the femur along the stridulatory file. 
However, the distance travelled during the io° change in the angle 
of the left femur between I'igs. io and 13 (inch) equals about 
0.6 mm at file level. Since about 22 pegs occur in 0.6 mm of file 
and 19 spikes appear in the frames mentioned, each acoustical spike 
^ one peg struck. 3 Such calculations depend on the file being per- 
pendicular to the femoral ridge, and parallel to the direction of 
stroke. Figures 3 and 4 show the convex curve of the file which 
would parallel rather accurately the path of the femoral rotation. 
Of course a one-legged male could solve the problem of interfemoral 
modulation. Motion pictures of such males in ideal positions for 
analysis have not yet been produced. 
Eisner (1974a) has published an elegant study of stridulations in 
several gomphocerine species, in which he also is impressed with the 
3 The correct spike count is from the calculated beginning of the synchro- 
nized oscillotrace with the image exposure to the end of the calculated 
synchronization (see Fig. 9). With each frame = 1.2 msec, the calculated 
frequency of 19 spikes per 4.1 msec synchronized oscillotrace corresponds 
to an average spike frequency of about 4650 Hz. Probably the file was 
first contacted by the left femur some distance posterior to the file’s proxi- 
mal end. These calculations are at variance by more than 10X with those 
of Pierce (1948, p. 250-254) who studied living specimens of A. sulphurea 
in eastern New England. He reported spike frequencies of the “insect at 
rest” of 360 Hz with a harmonic frequency of 7900 Hz. It is problematical 
whether this sound was the chirp or one of the other signals. 
Fig. 8 through 43. Ptenocinematographic sequence from the last frame of 
the upstroke (Fig. 8) and the entire downstroke of a unitary chirp filmed at 
800 (± 10) pictures per sec. Entire sequence is graphed in Fig. 44. 
Fig. 8, (a) oscillotrace of sound, (b) oscillotrace of 1600 Hz square wave 
(later calibrated at 1560), black arrows are along axes of measurement 
(right, left femoral axes, dorsal line of tegmen). Background grid, woven 
metal screening — 3 squares per cm. Amplitude of oscillotrace = 50mY/cm, 
square wave — X cm. 
Fig. 9, line at left illustrates the calculated synchrony of the audio oscillo- 
trace with the open shutter of the objective system (shutter speed is 0.5 
msec duration). 
Fig. 11 to 13, note regularity of oscillotrace as left femur begins down- 
stroke first and then the sonic (and perhaps mechanical) interference as 
the right femur begins the downstroke, the femoro-tibial angle is kept 
closed throughout. Fig. 22 shows probable sonic amplification as the femora 
move into phase. Finally, as left femur stops moving (Fig. 39), the sound 
of the right femur approximates the regular wave form and amplitude of 
Figs. 11 to 13. Refer to Fig. 44 for angle measurements and time relation- 
ships of the entire motion. 
