A comparative study on the song and morphology of Isophya stysi Čejchan, 1958 and Isophya modestior Brunner von Wattenwyl, 1882 (Orthoptera, Tettigoniidae)

We studied the song and morphology of Isophya stysi Čejchan, 1958, and Isophya modestior Brunner von Wattenwyl, 1882, two closely related bush-cricket species, treated as endangered in Hungary. Our main goals were to find song and morphometric characters that can be used reliably for the identification of specimens and to present comparative results that help us to see the relationship of the two taxa more clearly. We have found that the syllables of Isophya stysi always begin with 1–5 slowly repeated, distinct pulses, while in I. modestior, pulse-repetition rate was evenly high throughout the whole main pulse series of the syllable. Discriminant analysis showed that on the basis of their morphology, all the examined male specimens can be classified correctly to their song-based identification; furthermore, the arrangement pattern of stridulatory pegs also differed for the two species. Our results confirm that the two taxa are best treated as specifically distinct as they are distinguishable and the observed song differences may well be able to maintain reproductive isolation between them. We provide classification functions (based on four morphometric characters) that can be used confidently for the identification of males; however, we could not find any reliable method for identifying females from their morphology. Our results suggest that within I. stysi the population of the central-Transylvanian mountain range differs from the others by producing a higher number of pulses per syllable and having more stridulatory pegs and less elongated left elytron.