**2. Materials and methods**

48 Zoology

The sound on Orthoptera serves to promote social relations in the broadest sense of the term. This type of acoustic behaviour cannot be studied in isolation and cannot be understood except within the framework of the general behaviour of the species that is not just the sound production. From this point of view, we show that an exact knowledge of the physical elements of the sounds, as well as the morphology of these sound-producing organs is essential (Busnel, 1954). The sounds produced by the Orthoptera are important from a taxonomic point of view and has an important role as a mechanism of identification. They are of great value to establish the real status of local populations that may have few

The process of acoustic communication in reproduction is amply documented in Ensiferan insects (crickets and katydids): males of singing Ensifera (Orthoptera) emit specific calling songs used for species recognition, while courtship songs are generally less specific and could be mostly under the influence of sexual selection. In contrast, singing Caelifera (Orthoptera) perform more diverse behaviour prior to mating. In the subfamily Gomphocerinae (Acrididae) more specifically, many species emit calling songs, which are sufficiently specific to be used for species identification in the field, but they also perform very complex, often multimodal, courtship behaviour involving sequences of acoustic,

Neotropical Gomphocerinae form a group of grasshoppers whose taxonomy, systematics and biology are still poorly known (Otte, 1979; Otte & Jago, 1979). Within this group, *Rhammatocerus* Saussure, 1861 is widely distributed, from southern USA to central Argentine. Its species have a great economic importance; many of them are important crop and grazing pests (Carbonell et al., 2006; Cigliano & Lange, 1998; Salto et al., 2003), especially in Brazil and Colombia (Lecoq & Assis-Pujol, 1998). The genus *Rhammatocerus* is related to other genera such as *Parapellopedon* Jago, 1971 and *Cauratettix* Roberts, 1937.

Since its description, the most important studies on this genus are due to Jago (1971) and Carbonell (1995), but no taxonomical revisions of its entire species have been performed. At present, the genus is composed of 13 species (Assis-Pujol, 1997a 1997b, 1998; Carbonell, 1995), some of them still not clearly defined (Carbonell pers. comm.). The group is characterized by a high intraspecific variation and certain heterogeneity of its external morphology. So, other characters than morphological have been searched to clearly separate the species. As regards the species identification, in tribe Scyllinini, like in other Gomphocerinae, the genitalia allow differentiation between close species in only rare cases (Carbonell, 1995). The phallic complex is an important morphological character among Acrididae but, in Gomphocerinae, it has not a practical value (Carbonell, 1995). The female genitalia, especially the spermatheca, have revealed its utility in identifying some species (Assis-Pujol & Lecoq, 2000). Furthermore, molecular studies have not provided information

As pointed before, the sounds produced by Orthoptera are of great taxonomic value. They play a well-known role as identification system during mating, and for this reason they are of great value for establishing the real status of local populations that display small morphological differences (Blondheim, 1990; García et al., 1995). The study of sounds produced by Gomphocerinae has repeatedly demonstrated its utility to solve species identification problems (Ragge & Reynolds, 1998); however the acoustic behaviour of

vibrational and/or visual signals (Nattier et al., 2011; Ragge & Reynolds, 1998).

morphological differences (Blondheim, 1990; García et al., 1995).

helping species identification (Loreto et al., 2008).

This study on the sound production and stridulatory structures of *Rhammatocerus pictus* and *Rhammatocerus brunneri* was conducted with males and females proceeding from the "Colección de Entomología de la Facultad de Ciencias de la Universidad de la República", Uruguay, and specimens captured in Uruguay.
