Panel statement on young pine plants used for afforestation or reforestation as pathway for pinewood nematode (PWN) Bursaphelenchus xylophilus

Pinewood nematode (PWN) (Bursaphelenchus xylophilus) is a destructive pest of Pinus trees worldwide which depends for transmission on the cerambycid insects of the genus Monochamus. EFSA was asked to assess the potential role of young host plants for afforestation or reforestation planting as a pathway for PWN. According to legislation (EU COM/2023/415 final), these seedlings are not older than 2 years. Based on communication with SNPF (Syndicat National des Pépiniéristes Forestiers), such pine seedlings are assumed to have a collar diameter no more than 12 mm. It was evaluated that seedlings, by their physical dimensions, cannot sustain the complete developmental cycle of the vector insect Monochamus galloprovincialis. In particular, the reported empirical data on the minimum width of the head capsule of the phloem-based larval stage (L2) of 0.89–1.03 mm would not fit the 0.44-mm thick phloem of a 2-year-old pine tree, and the minimum 15-mm long pupal chamber with minimum observed inclination of 30° from the vertical of the heartwood, where L3 + L4 end feeding, would ultimately stretch beyond the 6-mm radius of the seedling and hence stick outside of the seedling. Observations of over 2000 beetle exit holes revealed that the branch diameter associated with successful insect development was larger than 20 mm, with a median of 90 mm. It was further evaluated that a vector-independent transmission between seedlings would necessitate direct contact of injured roots, which contrasts with prescribed procedures and good practice. The Panel considers the sequence of events leading to the transmission of nematodes through a seedling is highly implausible. Transmission would necessitate (i) nematode infestation of seedlings in a nursery, (ii) trade and planting of a symptom-free but nematode-infested seedling, (iii) its asymptomatic growth in the field to a tree size that allows vector development after years, (iv) the decline of this tree to attract vector egg laying while keeping nematodes in a developmental stage enabling insect vector transmission. Therefore, the Panel does not consider pine seedlings for afforestation or reforestation that are not older than 2 years and that have a root collar diameter of no more than 12 mm a pathway for PWN.