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.