Description
ORIGIN AND SPREAD. It is assumed that Bursaphelenchus xylophilus originated in North America and was accidentally introduced to the southern Japanese island of Kyushu via infected timber at the beginning of the 20th century, where it caused a veritable ecological catastrophe within a few years, leading to the death of plants belonging to the genus Pinus. From this first outbreak, it was subsequently reported in other Asian countries. In Europe, it was first found in Portugal in 1999 (Madeira) and later in Spain.
Monochamus species of concern, as known or possible vectors of B. xylophilus, are only found in the northern hemisphere and often the distribution range of these insects overlaps with the currently known range of the nematode.
HOST PLANTS The nematode is polyphagous within the genus Pinus, although it can be found on other conifers such as Picea, Abies, Larix, Cedrus, Chamaeciparis, Pseudotsuga, etc. The main forest species attacked are : Asiatic pines (P. bungeana, P. densiflora, P. luchuensis, P. massoniana, P. thumbergii) and European pines (P. mugo, P. nigra, P. pinaster, P. sylvestris).
BIOLOGY. Bursaphelenchus xylophilus is spread by vector insects, in particular cerambicid beetles of the genus Monochamus.
When, in late spring, Monochamus adults flicker emerging from dead wood trunks in which they have overwintered, and fly over healthy plants they begin to gnaw soft wood, producing wounds into which nematodes carried in their tracheae can penetrate. The nematodes, once they contaminate a healthy plant, change from larvae to adults and begin to reproduce in the resin ducts and cambial tissues of the plant. The plant, already compromised by nematode infestation, also becomes the target of fungal settlements carried by other insects(Ceratocystis spp., Ophiostoma piceae), which not only give the wood a bluish colour but also become a food reserve for the nematodes. Under favourable environmental conditions, Bursaphelenchus xylophilus reproduces very quickly, leading to the death of the plant within a few months, with progressive symptoms of desiccation.
The larvae of the nematode, feeding on fungi, approach the pupal chambers of the Monochamus larvae in diapause and when the insect turns into a pupa, the nematodes enter the Monochamus, which is about to flicker, restarting the infection cycle.
SYMPTOMATOLOGY. The first symptom of its presence is an evident reduction in the production of oleoresin in the attacked plants; leaf transpiration decreases and then stops altogether causing yellowing and wilting of the needles and the subsequent death of the host plant. Wilting may first appear on a single branch giving the characteristic 'flag-like' habit, but may affect the entire tree and show generalised symptoms.
PHYTOSANITARY CONTROL. In view of its high phytosanitary risk, this species is included in the list of quarantine pests of relevance to the European Union (Annex II, Part B of Regulation (EU) 2019/2072), and is considered one of the 20 priority quarantine pests in the Union. Indeed, as a harmful organism that has spread through the trade in infested wood, the greatest risk of its introduction is linked to the movement of wood packaging materials, with which most goods are transported in international trade.
In order to prevent this risk, the IPPC/FAO (International Plant Protection Convention) has approved an International Standard ISPM-15 which stipulates that packaging material must have undergone treatment (heat or fumigation) in order to circulate and then be duly marked.
REPORTS. To provide reports and receive information contact the Provincial Plant Protection Service (tel. 0461/495660; e-mail: serv.agricoltura@provincia.tn.it; pec: serv.agricoltura@pec.provincia.tn.it)
REFERENCE LEGISLATION. Regulation (EU) 2016/ 2031; Implementing Regulation (EU) 2019/2072; Legislative Decree No. 19/2021; Commission Implementing Decision (EU) 2018/618 of 19 April 2018.