Long‐term spatiotemporal genetic structure of an accidental parasitoid introduction, and local changes in prevalence of its associatedWolbachiasymbiont

Abstract

Population bottlenecks associated with founder events strongly impact the establishment and genetic makeup of populations. In addition to their genotype, founding individuals also bring along parasites, as well as symbionts that can manipulate the phenotype of their host, affecting the host population establishment, dynamics and evolution. Thus, to understand introduction, invasion, and spread, we should identify the roles played by accompanying symbionts. In 1991, the parasitoid wasp, Hyposoter horticola, and its associated hyperparasitoid were accidentally introduced from the main Åland islands, Finland, to an isolated island in the archipelago, along with their host, the Glanville fritillary butterfly. Though the receiving island was unoccupied, the butterfly was present on some of the small islands in the vicinity. The three introduced species have persisted locally ever since. A strain of the endosymbiotic bacterium Wolbachia has an intermediate prevalence in the parasitoid H. horticola across the main Åland population. The infection increases its susceptibility of to hyperparasitism. We investigated the establishment and spread of the parasitoid, along with patterns of prevalence of its symbiont using 323 specimens collected between 1992 and 2013, from five localities across Åland, including the source and introduced populations. Using 14 microsatellites and one mitochondrial marker, we suggest that the relatively diverse founding population and occasional migration between islands might have facilitated the persistence of all isolated populations, despite multiple local population crashes. We also show that where the hyperparasitoid is absent, and thus selection against infected wasp genotypes is relaxed, there is near‐fixation of Wolbachia.

Identity of wasp parasitoids (Hymenoptera) attacking Pieris brassicae (Linnaeus, 1758) (Lepidoptera: Pieridae) in South Africa

“…This mode of parasitoid introduction has occurred elsewhere, such as in the case of the 1991 accidental introduction of the Glanville fritillary butterfly (Melitaea cinxia Linnaeus, Nymphalidae), which included the parasitoid wasp, Hyposoter horticola (Gravenhorst) (Ichneumonidae: Campopleginae) and its associated hyperparasitoid Mesochorus cf. stigmaticus (Ichneumonidae: Mesochorinae), from the main Åland Islands in Finland to an isolated island in the archipelago (Duplouy et al 2021). To date no indigenous African wasp parasitoids have been reared from P. brassicae, and given the length of presence of the butterfly in South Africa it appears that they may not be able to adapt to this alien species, or that the conditions for host recruitment have not yet arisen.…”