Detection and Identification of the Invasive Sirex noctilio (Hymenoptera: Siricidae) Fungal Symbiont, Amylostereum areolatum (Russulales: Amylostereacea), in China and the Stimulating Effect of Insect Venom on Laccase Production by A. areolatum YQL03

The Eurasian woodwasp Sirex noctilio F. was first detected in Daqing, Heilongjiang Province, in the northeast region of China in 2013. Here, we investigated the S. noctilio's fungal symbiont, Amylostereum areolatum, and insect venom produced in its acid (venom) gland. Overall, seven out of 10 fungal isolates obtained from the mycangia of 10 adult S. noctilio females in this study were identified as A. areolatum. The remaining three isolates were identified as Trichoderma viride, Verticillium dahlia, and Geosmithia pallida, which were probably contaminants that entered during the mycangia-spore extraction process. The enzyme activity bioassay showed that the level of laccase activity of A. areolatum YQL03 in liquid medium is prominently enhanced by insect venom, but was relatively low when venom was not available as an inducer. This study confirms the presence of A. areolatum in S. noctilio specimens from China. The putative heat-stable factors identified in S. noctilio venom may contribute novel information about the pathogenic mechanism of the S. noctilio-A. areolatum pine-killing pest complex on host trees.

Biomarker genes highlight intraspecific and interspecific variations in the responses of Pinus taeda L. and Pinus radiata D. Don to Sirex noctilio F. acid gland secretions

Sirex noctilio F., a Eurasian horntail woodwasp recently introduced into North America, oviposits in pines and other conifers and in the process spreads a phytopathogenic fungus that serves as a food source for its larvae. During oviposition the woodwasp also deposits mucus produced in its acid (venom) gland that alters pine defense responses and facilitates infection by the fungus. A 26,496-feature loblolly pine cDNA microarray was used to survey gene expression of pine tissue responding to S. noctilio venom. Six genes were selected for further assessment by quantitative real-time polymerase chain reaction (qRT-PCR), including one that encoded an apparent PR-4 protein and another that encoded a thaumatin-like protein. Expression of both was strongly induced in response to venom, while expression of an apparent actin gene (ACT1) was stable in response to the venom. The pattern of gene response was similar in Pinus taeda L. and Pinus radiata D. Don, but the magnitude of response in P. radiata was significantly stronger for each of the induced genes. The magnitude of the biomarker gene response to venom also varied according to genotype within these two species. The qRT-PCR assay was used to demonstrate that the primary bioactive component in S. noctilio venom is a polypeptide.