Metapopulation structure of Cotesia melitaearum, a specialist parasitoid of the butterfly Melitaea cinxia

We describe a classical metapopulation structure in a threatened species of butterfly, Melitaea cinxia, and in its specialist parasitoid, Cotesia melitaearum, in a large network of small habitat patches. The incidence of the parasitoid in host populations was positively correlated with the size of the host population and the area of the habitat patch (dry meadows), and negatively correlated with isolation from existing parasitoid populations. Our results demonstrate that C. melitaearum increases the risk of local extinction of its host and may thereby play an important role in the metapopulation dynamics of the host butterfly. However, there is substantial population turnover in both species for reasons other than the host-parasitoid interaction as well. The parasitoid is affected by an abundant generalist hyperparasitoid, Gelis agilis, which showed a strong spatially density-dependent response to C. melitaearum cocoon group size, suggesting that it may contribute to population regulation of the primary parasitoid. We used an incidence function model to study the dynamics of the parasitoid metapopulation. The results indicate that the distribution of the parasitoid in the host populations is not at equilibrium, in agreement with the observed high turnover rate in the host metapopulation.