Monitoring of Bursaphelenchus xylophilus and focus on B. abietinus in the Italian territory

The pinewood nematode (PWN), Bursaphelenchus xylophilus, is one of the most important phytosanitary problems in conifers worldwide, as it can infest most Pinus species and other conifers, causing rapid wilting of the trees. It has been included in the EPPO A2 list as a quarantine organism and classified as a priority pest in the EU due to its serious potential economic, environmental and/or social impact (Regulation 2019/1702/EU). The risk of introduction and spread of PWN in Italy is high due to the intensive trade between the countries where the organism occurs and the availability of a wide range of susceptible hosts, as well as the presence of its vector on the Italian territory. According to the European legislation, annual phytosanitary surveillance programs are carried out to confirm the presence or absence of the pest in national coniferous forest stands. On the Italian territory, annual monitoring includes the sampling of standing declining and dead trees, pallets and bark mulch, and vector insects through baited traps. To date, no samples from the forest have tested positive for B. xylophilus, but a progressive and increasing decline in silver fir (Abies alba) stands has been observed for several years. More detailed investigations in these environments have made it possible to isolate numerous specimens of Bursaphelenchus abietinus from almost all the silver fir samples collected and analyzed. It is possible that this nematode contributes to the observed declines which, in combination with abiotic and biotic factors (e.g. temperature, drought and high density of bark beetles), can also lead to tree mortality. Further investigations on the pathogenicity of B. abietinus will be investigated in future studies.