Cicada orni L. is one of the most abundant and common species of cicada in Greece. However, this species was not found during recent field work on the Greek islands of Samos and Ikaria. Instead, the very closely related C. mordoganensis Boulard was found practically everywhere on these islands. C. orni and C. mordoganensis are very closely related species which are morphologically very similar (sibling species), even the male genitalia, and the acoustic signals produced by males during courtship and pair formation have the same general pattern. In order to describe the acoustic signals produced by these sibling species, temporal and spectral analyses were made of the calling songs of the males and certain acoustic variables were measured. Based on the duration of echemes, the number of pulse units they contain, the intervals between echemes and the number of echemes per second, the song of C. mordoganensis is distinct from that of C. orni. Cluster analysis of the acoustic characteristics of C. mordoganensis from Samos and Ikaria and of C. orni from the Greek mainland (Dionysos, north of Athens) gave a clear and distinct separation of these species.
Moreover, as there has been very little divergence between these two species at the protein electrophoretic level, the acoustic divergence has evolved independently of allozyme divergence. This may imply that in these cicadas acoustic divergence, and therefore premating isolation, may have evolved rapidly and resulted in rapid speciation at low levels of general genetic differentiation.
The aim of this study was to obtain information on the karyotypes, testes and ovaries of three fulgoroid families, mainly in the Issidae but also in the Caliscelidae and Acanaloniidae. For the Issidae, the data is for 19 species belonging to 11 genera of the subtribes Issina (2 species, 1 genus), Hysteropterina (14 species, 9 genera) and Agalmatiina (3 species, 2 genera) of the tribe Issini. The male karyotypes are shown to be quite uniform across the tribe, with 2n = 26 + X in all species studied except Latilica maculipes (Melichar, 1906) with 2n = 24 + X. The modal karyotype, 2n = 26 + X, matches the most probable ancestral state in the Fulgoroidea. In the majority of cases the number of seminal follicles in males and ovarioles in females are stable within but fairly variable among the species, the modal value of the follicle number is 10 per testis. Contrary to what might be expected from other fulgoroid families, such as the Dictyopharidae and Delphacidae, the variability in these characters revealed neither regular trends nor evident correspondence with the taxonomy of Issidae. In the Caliscelidae, all species studied had testes consisting of 6 follicles each and karyotypes of 2n = 24 + X and 26 + XY, respectively, in 3 and 1 species. The only representative studied of the Acanaloniidae, Acanalonia bivittata (Say, 1825), had 2n = 24 + X and 13 follicles in its testis. The variability in all the characters investigated is discussed and compared to other fulgoroid families, primarily to the most extensively studied families, Delphacidae and Dictyopharidae.