Charles S. Henry
Marta M. Wells
Dept. of Ecology & Evolution, Univ. of Connecticut, Box U-43, 75 N. Eagleville Rd., Storrs, CT 06269
Vibrational tremulation songs of Chrysoperla green lacewings have been shown to have a strong reproductive isolating effect on otherwise identical and interfertile populations, indicating the presence of cryptic, sibling species within the genus. The substrate-borne songs consist of pulses or volleys of abdominal vibration and are characterized by a modulated carrier frequency. To determine which features are essential for species recognition and how much change will be tolerated, synthetic songs were produced on a computer and played back to individual females of the common North American lacewing species, Chrysoperla plorabunda (Fitch). Responses of those females to selectively modified songs were then tabulated and compared to responses to unmodified songs. Song features tested included the first harmonic and modulation characteristics of the carrier frequency, as well as the length and spacing of the song volleys. It was found that females pay little attention to modest changes in volley duration, volley repetition rate, or fundamental frequency, but discriminate strongly against songs that lack smooth frequency modulation or that consist of random low-frequency noise. The significance of these findings to the evolution and speciation of members of the Chrysoperla plorabunda complex in North American and Europe is discussed.