Interactions between the Fungal Symbiont of Sirex noctilio (Hymenoptera: Siricidae) and Two Bark Beetle-Vectored Fungi

Abstract The woodwasp Sirex noctilio F. is invading North American forests, where it will interact with a large guild of pine-inhabiting beetles and their associated fungi. The woodwasp's obligate fungal symbiont, Amylostereum areolatum (Fries) Boidin (Stereaceae), plays an essential role in the wasp's larval development but is expected to be a poor competitor in the presence of fungi vectored by co-occurring insects. We examined the outcomes of competitive interactions between A. areolatum and two fungal species vectored by bark beetles, Leptographium wingfieldii Morelet (Ophiostomataceae) and Ophiostoma minus (Hedgcock) H. and P. Sydow (Ophiostomataceae), and the effect of temperature and substrate on these interactions. Beetle-associated fungi were usually able to capture more uncolonized resource than A. areolatum regardless of substrate or temperature. Amylostereum areolatum was able to colonize relatively more space in some cases but could not gain substrate already colonized by the ophiostomatoid competitor. These findings suggest that competitive interactions between beetle-vectored fungal species and A. areolatum could influence the reproductive fitness and distribution of S. noctilio within individual trees and also across a wide geographic area.