A Century of Invasion: How Biosecurity Influenced Populations of Sirex noctilio and Its Fungal Symbiont in Australasia.

The woodwasp, Sirex noctilio, and its mutualistic fungal symbiont, Amylostereum areolatum, are native to Eurasia and northern Africa. Sirex noctilio was first reported outside its native range in New Zealand in 1900, Tasmania in 1952 and mainland Australia in 1961. In this study, we consider the invasion history of these organisms across Australasia through population genetic analysis using mitochondrial sequence data and microsatellite markers and compared them with a previously published dataset from global collections. The study included contemporary (n = 461) and historical (n = 41) samples of S. noctilio dating back to 1952 and fungal (n = 176) samples from across the range. No population structure was found in Australian and New Zealand populations of S. noctilio or the fungal symbiont A. areolatum, reflecting both the natural (within the countries) and human-assisted (between the countries) spread of these symbionts. The S. noctilio populations in these countries had lower genetic diversity than other populations sampled globally. Amylostereum areolatum populations from Australia and New Zealand clustered separately from all other countries and were highly clonal. While the results suggested multiple early introductions in these two countries, it also reflected an efficient recent quarantine system that isolated these populations and reduced their complexity compared to other parts of the world. The findings also have relevance to the application of biological control for the pest complex.