Insect species introduced decades ago to small island has affected multiple insect populations – sciencedaily

Larvae of the Glanville fritillary butterfly, Melitaea cinxia, were introduced on the island of Sottunga in the Åland Islands, Finland, in 1991. The original research project for which this introduction was intended failed. However, although the island was previously butterfly-free, the displaced species have persisted, providing a ground for studying how an entire insect community might be affected by an introductory event.

“What researchers didn’t know 30 years ago was that the larvae carried the parasitoid butterfly wasp with them. Horticultural hyposoter. The parasitoid then carried its hyperparasitoid wasp Mesochore stigmaticus, and a bacterial symbiont transmitted from mother to offspring Wolbachia pipientis which somehow increases the susceptibility of the host H. horticola at Mr. stigmatic“, says Anne Duplouy, research fellow at the Academy at the University of Helsinki.

Through an annual survey of the Åland butterfly population, researchers at the University of Helsinki and Cornell University, USA, showed that the introduced butterfly population at Sottunga coped with several bottlenecks since 1991. It is therefore genetically quite reduced and faces a high risk of extinction.

“If the local butterfly populations are small and unstable, their parasitoids must be mobile enough to find hosts elsewhere. We were able to show that the parasitoid H. horticola is dispersive in Åland. In addition, it has persisted and shows less genetic structure than the host butterfly. This probably explains their genetic mixing with the populations of the neighboring island after introduction to Sottunga. The genotypes introduced have potentially prevented neighboring populations from becoming extinct during the decline of host populations, ”explains Anne Duplouy.

Hyperparasitoid Mr. stigmatic is not as mobile and has a smaller population, so it suffers from inbreeding and is absent from some islands. When the hyperparasitoid is absent, lines of parasitoids with Wolbachia can flourish.

“The genetic signature of the introduced wasp lineages gives us a window into what has happened in an island archipelago in the 25 years since their accidental introduction, including persistence through population bottlenecks, the dispersal and interbreeding, as well as sorting between lineages based on a hyperparasitoid and bacterial symbiont, ”explains Dr Saskya van Nouhuys of Cornell University, USA, who has been studying parasitoid populations in Åland since 1998.

Researchers are excited to see how genetic methods can complement ecological studies and be useful for studying and making inferences about a population introduced decades ago.

“We integrated methods of population genetics and population ecology to find interesting information on the ecology of hosts and parasitoids, as well as the influence of their bacterial symbionts over such a short period of time”, concludes academic researcher Dr Abhilash Nair from the University of Helsinki.

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