Discovery of an acoustically locating parasitoid with a potential role in divergence of song types among sympatric populations of the bush cricket Mecopoda elongata

The bush cricket Mecopoda elongata provides a striking example of sympatric intraspecific divergence in mating signals. Five completely distinct song types are found in various parapatric and sympatric locations in South India. While there is convincing evidence that population divergence in M. elongata is being maintained as a result of divergence in acoustic signals, cuticular chemical profiles, and genital characters, the causes of the evolution of such divergence in the first place are unknown. We describe the discovery of a tachinid parasitoid with an orthopteroid hearing mechanism affecting M. elongata. This parasitoid may have a role in driving the extraordinary divergence that had occurred among M. elongata song types. Over two years we sampled individuals of three sympatric song types in the wild and retained individuals in captivity to reveal rates of parasitization. We found that all three song types were infected with the parasitoid but that there were significant differences among song types in their probability of being infected. The probability of tachinid parasitization also differed between the two sampling periods. Therefore, it is possible that parasitoid infection plays a role in song type divergence among sympatric bush cricket populations.