294 
Psyche 
[June-September 
overall amplitude) volleys at 1/2 second intervals; each volley itself 
lasts about 1/3 second and is divided into a short, relatively intense 
initial section of 5-8 abdominal strokes and a longer, weaker portion 
of 20 or more strokes, every other one of which is usually empha¬ 
sized (Fig. ID). Part two consists of 10-20 distinctly different, shor¬ 
ter, simple volleys repeated every 1/5-1/4 second and each made up 
of 6-8 strokes of the abdomen; overall intensity is high at the onset 
of part two, but steadily declines almost to a null. Frequency of 
abdominal vibration is held fairly constant throughout, averaging 
68-80 strokes/second. Dueting insects, rather than interdigitating 
their solo sequences in the manner of C. carnea, alternate entire 
sequences politely with one another. Again, sexual differences are 
not profound in C. downesi, although during duets female sequen¬ 
ces are nearly always shorter than those of males (99 out of 127 
sequences). 
Discussion 
In summary, the calls of C. carnea and C. downesi differ greatly 
in overall complexity, duration, volley amplitude and frequency 
structure, and manner of exchange in heterosexual duets. Whereas 
C. carnea adults produce long homogeneous sequences of indeter¬ 
minate length and rapidly exchange volleys of jerking when dueting, 
those of C. downesi produce more structured sequences composed 
of two distinct classes of volleys and patiently exchange entire 
sequences when dueting. Additionally, pronounced frequency mod¬ 
ulation characterizes single volleys of C. carnea but not of C. dow¬ 
nesi. If, as is likely, the divergent calls function primarily to prevent 
interbreeding 2 , an allopatric origin of the two species is implicated. 
An alternative explanation of the observed dissimilarity in their 
“songs,” genetic drift following sympatric speciation, is not as con¬ 
vincing. It requires that two species showing grossly different calling 
patterns also display striking morphological similarity (Tauber, 
1974) and complete interfertility in the laboratory (Tauber and 
2 Species-specific calls can also originate in response to selective pressures unrelated 
to reproductive isolation—e.g., one type of call might communicate information 
more efficiently than another in a particular habitat. However, 1 am unable to 
identify any features of the two lacewings’ normal habitats that are simultaneously 
important to the production of sound and sufficiently different to account for the 
divergent calling patterns. 
