Hosts and their associated microbes are being increasingly introduced around the world, which can lead to novel host/microbe associations via new sympatries. Woodwasps (Hymenoptera: Siricidae) are able to utilize wood for its nutrients due to obligate mutualistic associations with white rot fungi in the genus Amylostereum and when invasive woodwasps are introduced to new areas, their symbionts accompany them. There is increasing evidence that woodwasp-fungus associations previously believed to be highly specific are actually flexible. We show that in North America, both Urocerus albicornis and Urocerus cressoni, which develop in trees in the Pinaceae, usually use Amylostereum chailletii but sometimes carry an Amylostereum areolatum strain putatively introduced to North America by the invasive woodwasp Sirex noctilio. Symbiont spillover from invasive to native hosts is a source of new host/introduced symbiont associations that could result in changes in microbes and host fitness with the potential to impact communities.
Keywords: Amylostereum; Fungal fidelity; Mutualist; Symbiont; Urocerus; White rot fungus.