Bioacoustics of Orchelimum

Diagnosis Body slender to robust, small to medium size as for the family; macropterous or mesopterous ( Figs. 3 A); tegumen smooth. Fastigium of vertex laterally compressed, rounded apically, never cone-shaped; no traces of genal carinae present; mandibles and labrum symmetrical; eyes relatively large. Pronotum short, lateral lobes approximately triangular, humeral sinus weak to well developed, posterior edge of lobe with well developed “secondary tympanum.” Stridulatory file with peg like teeth, strongly sinusoidal. All legs slender, fore and mid femora unarmed on lower margins. Male cercus always armed with one internal tooth; ovipositor weakly to distinctly curved, lower and upper edges of ovipositor parallel to divergent midlength.

Note: The genus Orchelimum is an example of a group maintained in the taxonomic literature by tradition rather than actual diagnostic characteristics that can identify it as a natural, monophyletic assemblage. Rehn and Hebard (1915a) present a combination of characters that supposedly identify Orchelimum as a genus distinct from Conocephalus , but even they admit that none of the characters is unique to Orchelimum and all of them occur, albeit less frequently, in Conocephalus . The only relatively consistent characteristics of Orchelimum spp. are their more robust appearance and larger body form, but even these characters broadly overlap with some species of Conocephalus . There are no consistent differences between the two genera either in the male or female genitalic structures, the male stridulatory apparatus, wing venation, leg armature, or any other structures considered diagnostic for Tettigoniidae . Glenn K. Morris (personal communication) provides two behavioral characters that may indicate a degree of separateness of the two genera. The dominant spectral peak of the male’s call in Orchelimum is in the acoustic range (about 18 kHz) whereas in Conocephalus (where unfortunately only a small fraction of species have ever been recorded) the dominant spectral peak is in the ultrasonic range (30 kHz and above). Morris notes, however, that “this song parameter is of course not unrelated to size, though it is not fair to say that frequency is simply dictated by size”. The second behavioral character apparently unique to Orchelimum is high incidence of male fighting, and many of the species known to fight do it by grappling. The latter is unknown to occur in males of Conocephalus . These observations, however, are based on a very limited number of species. Despite the lack of strong support for the separate status of the genus Orchelimum , it seems unwise to synonymize the two genera at this point as both names are well established in taxonomic literature and many species of Orchelimum are easily recognizable based on their larger size and sometimes distinct coloration. For the purpose of this review Orchelimum is treated as a separate, yet very closely related to Conocephalus genus of Conocephalinae s.l.

Description (male except where specified) Head.— Fastigium of vertex 0.75 to 1.4 times as wide as scapus ( Figs. 3 B-C), laterally compressed, rounded dorsally and apically, never hook- or cone-shaped, never projecting strongly in front of eyes; fastigium of vertex touching fastigium of frons. Eyes large relative to size of head, weakly protruding. Frons weakly convex, smooth; tegumen of head smooth, without traces of genal carinae; face slender to moderately wide. Mandibles and labrum symmetrical. Thorax and wings.— Dorsal surface of pronotum smooth, flat or metazona slightly raised; anterior dorsal margin straight, posterior one straight or weakly convex; lateral lobes approximately triangular, with acute posterior angle; posterior edge of lateral lobe with “secondary tympanum” – a somewhat raised, narrowly elliptical area of thinner cuticle covering thoracic auditory spiracle; humeral sinus poorly to well developed ( Fig. 3 A). Thoracic auditory spiracle large, elliptical, completely hidden under lateral lobe of pronotum; posterior edge of spiracle unmodified. Prosternum armed with two thin, short spines (modified basisternum); meso- and metasternum with lateral lobes of basisterna small, triangular, their inner margins touching; posterior part of metasternum strongly compressed causing hind coxa to nearly touch each other. Wings in both sexes fully developed, surpassing apices of hind femora , rarely somewhat shortened and not reaching hind knees; hind wings usually distinctly longer than tegmina. Stridulatory apparatus of male well developed; stridulatory area of left wing membranous, without a network of secondary veinlets; stridulatory file (vein AA1—new vein homology after Kukalova-Peck, personal communication; male stridulatory file used to be homologized with the vein Cu2) sinusoidal ( Fig. 41 A), teeth thick, peg-like, sparsely arranged, especially on distal end of file; mirror of right wing approximately rectangular, with secondary veinlet next to AA1 always well developed, divergent from AA1. Legs.— All legs long and slender; fore coxa with an elongate, forward projecting spine dorsally. All femora unarmed dorsally; fore and mid femora unarmed ventrally, hind femora armed ventrally with relatively few minute spines or unarmed; genicular lobes of femora usually armed with short spines. Fore and mid tibiae unarmed dorsally, both ventral margins with immovable spines as long as 1/4 to 1/2 diameter of tibia; hind tibia armed on all four dorsal and ventral margins; apex of tibia with two pairs of ventral and one pair of dorsal movable spurs. Tympanum on fore tibia bilaterally closed, tympanal slits facing forward, tympanal area weakly to distinctly swollen, with pair of small, elongated pits below tympanal slits. Abdomen.— Dorsal surface of abdominal terga smooth, unmodified. Male 10th tergite usually strongly sclerotized, with narrow apical incision, supraanal plate small, triangular. Male cercus always with one internal spine, often accompanied by more or less developed dorsal, sinusoid groove ( Fig. 41 C); female cercus, simple, slender and weakly incurved. Subgenital plate of male with a pair of styli, distinct median keel, truncated apically ( Fig. 3 D) or with triangular apical emargination; female subgenital plate approximately triangular, rounded or shallowly emarginated apically. Concealed genitalia of male with paired, heavily sclerotized, hook-like titillators ( Fig. 3 E). Ovipositor narrow, straight to distinctly curved; its length variable, from less than half the length to almost as long as hind femur; both dorsal and ventral margins of ovipositor smooth, parallel to divergent midlength; apex of upper valvula sharp ( Fig. 3 F). Coloration.— General coloration green to brown, almost invariably with dark, wide stripe on head and pronotum; head sometimes red dorsally ( O. erythrocephalum Davis ) or face with median brown stripe ( O. concinnum Scudder ); abdomen green or yellow; sometimes dorsal side of abdomen yellow, with dark, longitudinal stripes. Tegmina straw brown to light green; legs green to light brown.