On Mon, 28 Aug 1995, Richard Jensen wrote:

A very elegant demonstration of an isolating mechanism operating in leafhoppers was presented at the 8th International Auchenorrhyncha Congress in Delphi in 1993 by Hildegard Strubing. Dr Strubing showed a videotape she had made of mating behaviour between two closely related species of cicadellids. Female leafhoppers use a characteristic substrate vibration to "call" the males. The videotape showed the female making her call and the male responding and approaching. Finally the male parked himself next to the female, stretched his abdomen under her abdomen and connected. The pair then rotated so they were facing away from each other with the tips of their abdomens held tent-like between them and they settled in that position for sperm transfer. The videotape then went on to show the same sequence with the male of a different, but closely related, species. The same female made the same call, the male responded and approached. When he was alongside the female, his abdomen reached under hers, just as the other male's had done and they connected. However, when the two turned to face away from each other in the usual mating position, the connection came loose and every time they attempted to mate the connection was broken. The tape then went on to show another successful mating by the same female with the "correct" male.

This demonstrated to me the importance of the morphology of the male genitalia as an isolating mechanism for cicadellids. The male genitalia have long been recognised as providing extremely valuable characters for specific diagnoses throughout the Auchenorrhyncha but this video demonstrated the biological relevance of this for isolating the species. It also showed that the "calls" produced by closely related species had little impact on species isolation.