Conclusion
The study of invasion, and of accidental or intentional introductions of
species are central to much of contemporary population and community
ecology (Davis, 2009). Parasitoids are used as insect biological control
agents (Wang, Liu, Shi, Huang, & Chen, 2019). Consequently, they are
intentional introduced into both agricultural and natural environments
(Grangirard, Hoddle, Petit, Roderick, & Davies, 2009) but often these
introductions do not persist in the long term (Goldson et al., 2014),
and if they do, their genetic structures might differ (Hufbauer et al.,
2004). Brought along during the introduction events, associated
symbionts can impact the success story of their host populations, by
affecting the phenotypes and genotypes of their hosts (Charlat et al.,
2009; Hornett et al., 2006). We use genetic evidence to document the
trajectory of a successful introduced parasitoid population over 22
years. We show persistence of the wasp on the previously uninhabited
island, and spread of the transplanted genotypes to surrounding island
populations, along with the associated symbiotic bacteriumWolbachia. The shuffling of the nuclear and matrilineally
inherited markers among islands suggests differential selection for the
infection-associated genotypes in the local host genetic pools under
relaxed predation pressures in an island where the hyperparasitoid
species is absent (van Nouhuys et al., 2016). The establishment of newly
introduced parasitoid genotypes might contribute to either the
persistence of the isolated island wasp populations, or the replacement
of the local wasp populations, or both. It may have also changed
environment for the pre-existing nearby isolated butterfly host
population, which previously did not have the parasitoid. The Glanville
fritillary butterfly is vulnerable to loss of genetic variability and
extinction in the Baltic Sea region due to habitat fragmentation, and
has gone extinct from the Turku archipelago in southwest Finland
(Fountain et al., 2016). The spread of an introduced parasitoid
population can represent another pressure for the host population, as
well as any competing local parasitoid populations (Benson, Van
Driesche, Pasquale, & Elkinton, 2003; Benvenuto, Cheyppe-Buchmann,
Bermond, Ris, & Fauvergue, 2012). This is especially true if newly
introduced parasitoid genotypes show greater fitness than native
genotypes (Dupas, Dubuffet, Carton, & Poirie, 2009; Kraaijeveld, Van
Alphen, & Godfray, 1998; van Nouhuys, Niemikapee, & Hanski, 2012).