Detection and identification of Amylostereum areolatum (Russulales: Amylostereaceae) in the mycangia of Sirex nigricornis (Hymenoptera: Siricaidae) in central Louisiana
The woodwasp Sirex noctilio F. (Hymenoptera: Siricidae) has become established in North America. A primary tactic for the management of S. noctilio in the southern hemisphere has been the development of a biological control agent, Deladenus siricidicola Bedding. This nematode has a bicyclic life cycle including a mycetophagous free-living and parasitic cycle. During oviposition, female Sirex woodwasps inject a symbiotic fungus. Because D. siricidicola only develops well on Amylostereum areolatum (Chaillet ex Fries) Boidin (Russulales: Amylostereaceae) and North American woodwasps were thought to all have Amylostereum chailletii (Persoon) Boidin as their fungal symbiont, the risk of unintended impacts from D. siricidicola in North America was considered low. Specific polymerase chain reaction primers were designed to amplify the intergenic spacer region of Amylostereum symbionts in a population of the native woodwasp Sirex nigricornis F. located in central Louisiana (i.e., well outside the known distribution of S. noctilio); identity of the symbiont was confirmed by phylogenetic analyses. Overall, 95 out of 100 fungal isolates obtained from the mycangia of S. nigricornis were identified as Amylostereum species. Contrary to expectations, 60% were identified as A. chailletii (N 60), while 35% were identified as A. areolatum (N 35). The remaining 5% of these isolates (N 5) were identified as Bipolaris papendorfii (Aa) Alcorn, Alternaria alternata (Fr.) Keissl, Penicillium marneffei Segretain, Scytalidium cuboideum (Sacc. & Ellis) Sigler & Kang, and Hyphopichia heimii (Pignal) Kurtzman based on sequencing of the internal transcribed spacer (ITS) region. The five non-Amylostereum isolates were likely contaminants during mycangia-spore extraction process. This study confirms the presence of A. areolatum in a population of the native woodwasp S. nigricornis well outside the known distribution of S. noctilio.