RESUMO
The vibrational communication and mating behaviour of the graminicolous leafhoppers Zyginidia pullula, Z. ribauti, Z. scutellaris, Z. serpentina, Z. sohrab, and Z. biroi were investigated to explain why the first five species hybridize. Z. biroi was used as a control species. All species behaved in the same way and no significant statistical differences were detected with regard to male calls, while female calls and the male courtship song differed in Z. biroi, thus showing that a specific pre-mating isolation mechanism was used by the latter species and the first five ones lacked such a mechanism. In addition, Z. sohrab is missing in Italy, while the other species live allopatrically in Italy, with the only exceptions being Z. serpentina and Z. biroi, which live in Sicily and are often found in sympatry, and Z. scutellaris and Z. biroi, which live in Sardinia. All these species can be distinguished by means of male genital appendages; however, Z. biroi is longer and has a different body colour. The existence of natural hybrids of Z. pullula, Z. ribauti, and Z. scutellaris in the Italian peninsula and their hybridization in the laboratory with Z. serpentina and Z. sohrab require the investigation of possible post-mating reproductive barriers before re-considering their systematic validity.