The importance of male and female acoustic behaviour for reproductive isolation in Ribautodelphax planthoppers (Homoptera: Delphacidae)

The importance for reproductive isolation of species-specific acoustic differences between closely related Ribautodelphax planthopper species is tested by measuring responses to playbacks of both conspecific and heterospecific signals. Females respond to heterospecific male calls at about 80% of the conspecific response level, irrespective of the degree of cross-insemination of the combination involved. In a combination involving R. albostriatus , a taxonomically more distantly related species, female response levels are only 15–33% of the normal level. Study of the development of both female responsiveness and receptiveness shows that response levels correspond fairly well with insemination levels. Female heterospecific response is far too high to explain isolation between the species. Female answers to heterospecific males calls have normal response-delay times and durations. When offered a two-way choice between female playback calls, males significantly more often approach the conspecific call in almost all combinations tested. Offering only a heterospecific female signal induces males to call, but not to search. Males are capable of maintaining at least part of the sexual isolation by distinguishing between different female calls. This seems in conflict with the popular theory that the sex with the greater parental investment, here the female, should be exerting the choice.