Multilocus Genotyping and Intergenic Spacer Single Nucleotide Polymorphisms of Amylostereum areolatum (Russulales: Amylostereacea) Symbionts of Native and Non-Native Sirex Species

Functional and Compositional Changes in Sirex noctilio Gut Microbiome in Different Habitats: Unraveling the Complexity of Invasive Adaptation

The mutualistic symbiosis relationship between the gut microbiome and their insect hosts has attracted much scientific attention. The native woodwasp, Sirex nitobei, and the invasive European woodwasp, Sirex noctilio, are two pests that infest pines in northeastern China. Following its encounter with the native species, however, there is a lack of research on whether the gut microbiome of S. noctilio changed, what causes contributed to these alterations, and whether these changes were more conducive to invasive colonization. We used high-throughput and metatranscriptomic sequencing to investigate S. noctilio larval gut and frass from four sites where only S. noctilio and both two Sirex species and investigated the effects of environmental factors, biological interactions, and ecological processes on S. noctilio gut microbial community assembly. Amplicon sequencing of two Sirex species revealed differential patterns of bacterial and fungal composition and functional prediction. S. noctilio larval gut bacterial and fungal diversity was essentially higher in coexistence sites than in separate existence sites, and most of the larval gut bacterial and fungal community functional predictions were significantly different as well. Moreover, temperature and precipitation positively correlate with most of the highly abundant bacterial and fungal genera. Source-tracking analysis showed that S. noctilio larvae at coexistence sites remain dependent on adult gut transmission (vertical transmission) or recruitment to frass (horizontal transmission). Meanwhile, stochastic processes of drift and dispersal limitation also have important impacts on the assembly of S. noctilio larval gut microbiome, especially at coexistence sites. In summary, our results reveal the potential role of changes in S. noctilio larval gut microbiome in the successful colonization and better adaptation of the environment.

Pest categorisation of Sirex nitobei

The EFSA Panel on Plant Health performed a pest categorisation of Sirex nitobei (Hymenoptera: Siricidae), the nitobe horntail, for the territory of the EU. S. nitobei is not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072 but was identified as a potential regulated pest in a commodity risk assessment of Pinus thunbergii artificially dwarfed plants from Japan. This species is present in Japan (except Hokkaidō), the Republic of Korea and 13 Chinese provinces. S. nitobei attacks several Pinus species and has been reported less frequently on Abies firma and Larix spp., including L. leptolepis. The females oviposit into the sapwood. Eggs are deposited together with a phytotoxic mucus and a symbiotic fungus, Amylostereum areolatum or A. chailletii. The combined action of the venom and the fungus results in the death of the host trees. The fungus degrades the lignocellulosic components of the wood, and the larvae feed on the liquid fraction of the digested residues left by the fungus. All immature stages live in the hosts sapwood. The lifecycle of the pest lasts 1 year. S. nitobei can travel with conifer wood, wood packaging material or plants for planting, but these pathways from third countries are closed by prohibition. However, a derogation exists for artificially dwarfed Japanese black pine (Pinus thunbergii) from Japan, which therefore provides a potential pathway. Climatic conditions in several EU member states and host plant availability in those areas are conducive for establishment. The introduction of S. nitobei is potentially damaging for pines. Phytosanitary measures are available to reduce the likelihood of entry and further spread, and there is a potential for biological control. S. nitobei satisfies all the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.