Eumecopoda cyrtoscelis (Karsch, 1888)

Morris, Glenn K, Ingrisch, Sigfrid, Willemse, Fer, Willemse, Luc, De Luca, Paul A. & Klimas, Dita, 2025, Stridulation songs of some Tettigoniidae (Ensifera, Orthoptera) from Papua New Guinea, Zootaxa 5600 (1), pp. 1-81 : 26

Eumecopoda cyrtoscelis (Karsch, 1888)

( Figs 22 –25, 30, 31, 82AB)

Specimens studied. PNG, Wau W.E.I. 30 vii & 4 viii & 23 viii 1981, remnant forest understory, G.K. Morris 3 males; Bulolo Gorge, McAdam Nat. Pk., 28 viii 1981, G.K. Morris (1 female). (Depository NBC Leiden) .

Systematics. .The specimens agree with the nominate form.

Habitat. Found on low vegetation alongside forest paths. Both Eumecopoda spp. descended to the bottom of their cages during the day becoming immobile. But when disturbed they reacted explosively: Dita was very effectively startled when she investigated one inert male that suddenly leaped away. Once it gets dark the insects climb back up in their cages and begin to sing.

Stridulation. Each E. cyrtoscelis call continues for several seconds at a time ( Fig. 30A ) and each call initiates with single high intensity sound (see arrow in Fig. 30A ). At increased time resolution these calls are seen to be composed of two sorts of simple sine waves, i.e., two different carrier frequencies ( Fig. 31A–C ). There is a less intense higher frequency and a more intense lower frequency. Both carrier frequencies, 3.1 and ~6.7 kHz, lie in the low audio range and are harmonically related, alternating rather than co-occuring, so providing an example of resonance stridulation together with sequential frequency modulation. Both species are very loud to healthy human ears. On first hearing calls in the field we remarked on the song’s odd quality, perhaps a response to the rapid alternation of the two close harmonics.

This would appear to be an instance of resonance stridulation. Yet the presence of the overmirror fold and a large terminal swelling blocking the basad terminus of the file, the lack of typical katydid count in file teeth: these are oddities of strigin morphology that suggest a differently functioning sound generator. See the Discussion for an attempt to imagine the workings of this strigin.

The spectral peaks ( Fig. 30D ) are quite high-Q even though the pulses are comprised of only two dozen waves. Yet there is little or no transient distortion. Perhaps this is because the pulses build slowly and slowly decay ( Fig. 31 BC). “The amount of transient distortion varies as a function of the time required for the amplitude to rise from zero to maximum or to decay from maxiumum to zero. …slowly rising and slowly decaying signals are characterized by less transient distortion than signals for which the amplitude rises and decays very quickly” ( Speaks 1992).

Figures

FIGURE 22. Eumecopoda cyrtoscelis (SEM). Dorsal aspect FIGURE 23. E. cyrtoscelis (SEM). Oblique view ventral of right tegmen shows mirror speculum below cantilevered aspect anal region right tegmen, shows charging ovoid ‘over-mirror fold’ (omf); wing base to upper left. Two-side speculum and harp; wing base (and scraper) upper right. charging of speculum and small area behind scraper indicates their thinness. Short but strong unguiform curved vein (cv) projects into the speculum.

FIGURE 30. E. cyrtoscelis acoustic analysis: A) At coarse time resolution 5 calls follow lower intensity ‘warm-up’, each call starts with brief high-amplitude emission; B) Onset detail of the last song of A (arrow); C) higher time resolution of a portion of this fifth call; D) spectrum showing emission of two high-Q audio peaks [3.1 kHz, 6.7 kHz] separated by about 3 kHz (harmonically related); call devoid of ultrasonics.

FIGURE 31. E. cyrtoscelis acoustic analysis: A) 3 pulse pairs of alternating low and high-magnitude sinusoids; B) lower amplitude pulse in A has higher frequency wave; C) higher amplitude pulse in A has the lower frequency wave.