1974] 
W ussow et at. — Sounds and Motions of Insects 
215 
allowance for the time lag induced by the speed of the original sound 
in air (PL if, arrows). 
9) Close examination of CRTs can be a health hazard and the 
thickness of the protective cover can induce parallax error. There- 
fore, if exact angle and displacement measurements are desired the 
fields should be photographed with careful focussing on the video 
lines. Such photographs will form a permanent working record of 
key fields of the rather fragile video-tape which can be damaged or 
destroyed by the constant friction of scanning in the stopped position. 
Discussion and Conclusions 
This method allows relatively synchronous visualization of motions 
and the sounds produced by the movements if the actions are rela- 
tively slow. For example, it is possible to determine whether the stri- 
dulation by a single up-down motion of a grasshopper’s hind femur 
rubbing against the fore-wing is produced during the up-stroke or 
down-stroke, provided the entire motion has a duration of >60 msec. 
In the case of oedipodine grasshoppers, the chirps produced by males 
during courtship usually are produced by motions which last at least 
60 msec and often 100 msec (Willey, 1974). Since many such sig- 
nals are complicated by being segmented into pulses within a single 
up-down motion, normal-speed cinematographic and audiospectro- 
graphic investigations of Oedipodinae (Otte, 1970; Willey & Willey, 
1969) have concluded that the first pulse must be produced on the 
up-stroke. However, high-speed motion analysis (Willey, 1974) 
shows that Arphia sulphur ea produces the definitive chirp on the 
downstroke only. A very weak signal was produced on the up-stroke 
but was of such low amplitude that it had never been audiospectro- 
graphed. Video-tapes of Chimarocephala (Loher & Chandrashekaran, 
1970) and Chortophaga (Steinberg & Willey, 1974) also show that 
stridulations are produced only on the downstroke of the femur in 
these species. However, the mechanism for production of two-pulsed 
chirps must be analyzed by the higher speed methods (Willey, 1974). 
Further refinements of this system can involve direct synchrony of 
oscillotrace with the initial video-tape recording. Also the use of a 
light-emitting diode (LED) and a small high speed digital clock in 
the background, synchronized with each video field, would simplify 
identification of particular fields. However, the method we have 
reported can be used for improving the analysis of already existing 
tapes. 
