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, spread, and dynamics
of a parasitoid species introduced into a new habitat along with its
host butterfly. Because the parasitoid carried along itsWolbachia 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 during population
fluctuations across its 22 years of persistence, and potentially in the
founding generation. Additionally, the introduction might have affected
the genetic pool of the population inhabiting the nearby islands through
dispersal of individuals carrying the mainland genotypes, and by the
establishment of populations carrying a costly Wolbachia strain.