Melanonotus powellorum Rentz, 1975

M. powellorum is a recently described species (Rentz 1975) of Monte Verde. Its song at 24 C in the laboratory was a sequence of raspy triple-train chirps, given at a chirp rate of 2/s (Fig. 12). The silent interval between the first and second train is substantially longer than that between the second and third. The pulses are sinusoidal and their frequency, calculated from the wave form, corresponds to the high-Q 25 kHz spectral peak revealed by the analyser.

The songs of M. powellorum and A. circumdatus show an in teresting convergence with that of M. sphagnorum, the Canadian decticine mentioned above. M. sphagnorum also produces short trains of 10-15 wave, ultrasonic pure tone pulses (Morris 1970). The carrier frequencies of these pulses are very similar in A. circum datus and M. sphagnorum, 32 and 33 kHz respectively; the carrier of M. powellorum, 25 kHz, is at least of the same order. The time relationship of these pulses suggests that each train is generated during a single tegminal closure. The stridulation of M. sphagnorum has been analysed using flash photography to cor relate song elements with tegminal displacement (Morris & Pipher 1972). A mechanism proposed for the decticine may plausibly be invoked for the two pseudophyllines: during a single run down the file, the scraper lodges at intervals behind a tooth, then drives at high speed over the next 10-15 teeth before lodging again. In this way elastic energy stored in the tegminal cuticle (scraper lobe) is made the basis of generating an ultrasonic high-Q sound.

Tremulation is a body-oscillating behaviour which generates vibrations in plant substrate. It has been described in the neotropical katydid Copiphora rhinoceros (Morris 1980). M. powellorum was observed to tremulate in the laboratory. It under went bouts of rapid body-shaking, each bout sustained through 20 or more oscillations. This was performed with the insect perched both vertically, on the side of a glass-walled cage, and horizontally on a metal screen. The movements were not as stereotyped as in C. rhinoceros.[1]

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