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Psyche 
[Vol. 88 
and backward in front of the female, and sometimes even sideways. 
Especially vigorous males were seen to perform small jumps, 
reminiscent of take-off behavior. 
A chrysopid usually flies with its head higher than its abdomen. If 
the insect is mounted on a flight mill and illuminated with a strobe 
light, the abdomen can be seen moving up and down in the same 
way as described for the courtship behavior (Fig. 2). When mounted 
horizontally, the abdominal movements were exaggerated (Fig. 3). 
In both orientations the strobe flashes revealed that the frequencies 
of the wing beat and of the abdominal vibration were the same. 
With each down-stroke of the wings the abdomen was lifted (Figs. 3 
and 4). The flow of the movements can be seen in Fig. 5. 
Observations made during this study indicate that the wing beat 
frequency was positively correlated with temperature and, in gen- 
eral, negatively correlated with wing length. At 23° C, a wing beat 
frequency of 27 Hz (strokes /sec) was recorded for C. carnea and 38 
Hz for the smaller M. basalis. Miller (1975) reported similar results, 
25 Hz at 21-24°C in tethered flying C. carnea. 
Discussion 
The frequencies of abdominal vibration during courtship have 
been reported for three species of Chrysoperla. For C. rufilabrus the 
rates were 14-18 Hz (Henry 1980a). No temperature data were 
given. In C. carnea the frequencies varied from 30 to 100 Hz at 
24-28° C (Henry 1980c), while the courtship behavior of C. downesi 
included volleys of abdominal vibration with a frequency of 60-80 
Hz, with a mean of approximately 73 Hz, at 24-29° C (Henry 
1980b). 
The greater variability in the frequencies of abdominal vibration 
during courtship, relative to flight, is probably related to two 
factors. First, there is no minimum rate of wing beats necessary to 
maintain flight. Second, the maximum possible rate is increased, 
since the wings merely vibrate rather than making full strokes. 
These would open a wide range of frequencies for chrysopids to use 
in tremulation. If character displacement occurred, as hypothesized 
by Henry (1980b), this would tend to expand the range of frequen- 
cies actually used by chrysopids. 
Tremulation has also been reported in the courtship behavior of 
other groups of insects. Plecoptera communicate via the substrate 
by drumming with their abdomens (Rupprecht 1968). Similar 
