Recognition of calls with exceptionally fast pulse rates: female phonotaxis in the genus Neoconocephalus (Orthoptera: Tettigoniidae).

Male Neoconocephalus robustus and Neoconocephalus bivocatus produce remarkably fast calls, with pulse rates of approximately 175-200 Hz. The temporal call patterns differ significantly between the two species. Male N. robustus produce calls with a single pulse rate of 200 Hz. In N. bivocatus, pulses are repeated with alternating periods, resulting in distinct pulse pairs: approximately 175 pulses s(-1) are grouped into 87 pulse pairs s(-1). In order to identify the temporal parameters used to recognize calls with such fast pulse rates, female call recognition in both species was tested during phonotaxis on a walking compensator. Female N. robustus were attracted to calls without amplitude modulation. Amplitude-modulated signals were equally attractive, as long as the silent intervals were short enough. The maximally tolerated interval duration varied with pulse duration. Female N. bivocatus did not require the paired-pulse pattern but were attracted to call models in which each pulse pair was merged into one long pulse. Females used the pulse rate to recognize such signals: pulse rates close to 87 Hz were attractive, largely independent of the duty cycle. Thus, females of the sibling species N. robustus and N. bivocatus used qualitatively different call recognition mechanisms.