Discussion
The introduction and long-term persistence of the parasitoid waspH. horticola in the small island of Sottunga, on the East side of the Ă…land archipelago, offered a unique opportunity to investigate the spatio-temporal changes in the genetic structure, dispersal, and dynamics of a species introduced into a new habitat. Because the parasitoid carried along its Wolbachia symbiont, we could also investigate how symbionts might affect the spread of different host genotypes after introduction. Our results suggest that the H. horticola population that established in Sottunga persisted despite strong bottlenecks both during the founder event, and across its 22 years of persistence. Additionally, the introduction affected the genetic pool of the insect communities inhabiting the nearby islands through dispersal of individuals carrying the mainland genotypes, and by the establishment of populations carrying a costly Wolbachiastrain.