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[Vol. 85 
receptive, produce brief, repetitive volleys of low-frequency abdom- 
inal vibration at (approximately) one-second intervals for up to 
several minutes at a time (Henry 1979, 1980c); in heterosexual duets, 
the two partners alternately and repeatedly exchange single volleys 
until copulation is achieved. Each volley in Ch. plorabunda is 
characterized by a smoothly increasing and then decreasing ampli- 
tude envelope and by pronounced frequency modulation (see 
Fig. 1): the rate of abdominal vibration gradually declines to less 
than half its initial value during the course of the volley (Henry 
1980c). 
Green lacewings of the genus Chrysoperla are unusual among 
acoustical animals in that females are just as likely to sing as males 
(Henry 1983b). In contrast, males alone (or principally) sing and call 
conspecific females to them in most species of the best studied 
animal taxa like birds (Catchpole 1982), lizards (Frankenberg 1982), 
frogs (Littlejohn 1977), katydids (Dumortier 1963), homopterans 
(Ossiannilsson 1949, Young 1980), and crickets (Walker 1962, 
Dumortier 1963). Such unilateral male signalling has been inter- 
preted in most acoustical animals as indicative of sexual selection 
operating on the higher variance in reproductive success of males 
(Halliday 1978, Otte 1974, Alexander 1975). On the other hand, the 
unusual presence of calling behavior in both sexes of Chrysoperla 
species may stem from the proven importance of their vibrational 
signals in the reproductive isolation of closely related species. For 
example, neither of the sibling, interfertile species Ch. plorabunda 
and Ch. downesi (Banks) will respond to the song of the other, thus 
precluding courtship duets and preventing interspecific mating 
under natural conditions (Henry 1983b). If such signals are to be 
effective as reproductive isolating mechanisms, however, they must 
remain unambiguous to recipients over the wide range of tempera- 
ture typically experienced by lacewings in the field. Abundant doc- 
umentation exists of gross alteration in chirp rate, wing-stroke 
frequency, pulse or chirp duration, or call notes by temperature 
changes in many taxonomically disparate insect groups (Brooks 
1882, Hayward 1901, Alexander 1956, Walker 1962, Dumortier 
1963, Shaw 1968, Booij 1982), and similar temperature-related 
changes should be characteristic of lacewing songs (see Henry 1982b 
for preliminary work on Chrysopa oculata Say). One would also 
predict that the calls of the two sexes of a given species of Chryso- 
perla should vary in a closely parallel fashion over a wide range of 
