EFSA assesses pine wood nematode threat

EFSA has concluded that the stone pine, a tree species found widely in Portugal and Spain, must still be considered a potential host for pine wood nematode. The Authority’s Panel on Plant Health called for further research to assess the threat posed by this pest to European trees.

The conclusions are part of a scientific opinion on the phytosanitary risk associated with some coniferous tree species for the spread of pine wood nematode (Bursaphelenchus xylophilus), a significant disease present in North America and the Far East. In Europe the problem is largely confined to mainland Portugal, which suffered a first outbreak of pine wood nematode in 1999, and which is subject to emergency measures to prevent its further spread[1].

The nematode causes pine wilt disease, which results in the sudden death of pine trees. Susceptible coniferous tree species suffer invasions of the pest through the feeding or egg-laying scars created by nematode-carrying beetles.

The Commission asked the Panel on Plant Health specifically to clarify the risk associated with the species Pinus pinea, the Mediterranean stone pine, following a request from Portugal and Spain that it be removed from the EU’s list of plants considered susceptible to the nematode. The Panel was also asked to look at plants belonging to the genera Chamaecyparis, Cryptomeria and Juniperus, which are not on the EU’s list of susceptible plants[2].

On P. pinea, the Panel undertook a comprehensive literature review and analysed a risk assessment submitted by Portugal. They rejected the assertion in the Portuguese dossier that P. pinea is not a host plant for the pine wood nematode, pointing out that the small number of P. pinea trees sampled in the study was insufficient to support such a conclusion and that the results could not be extrapolated to other areas of Portugal. The Panel also cited evidence that other coniferous trees in North America can become infested with the pine wood nematode but remain free of symptoms for many years.

With regard to the vector beetle Monochamus galloprovincialis, the Portuguese study reported an experiment which showed a relatively low rate of egg-laying on P. pinea compared with the susceptible species Pinus pinaster. However, the EFSA Panel pointed out that oviposition (egg-laying) on P. pinea was still possible and also concluded that the finding from the experiment could not be extrapolated to forests with different tree compositions and environments.

In addition, the Panel noted that M. galloprovincialis is distributed over a vast geographical area and local populations could have host preferences different from those of the beetles found in Portugal. For example, attacks on P. pinea by M. galloprovincialis have been recorded in Italy.

Overall, the Panel considered the risk of pine wood nematode spreading through the plants and wood of P.pinea to be low if trade volumes are small. However, they emphasised that this assessment is highly uncertain, because of the lack of data concerning the interaction between the vector beetles, the nematode and P. pinea.

The Panel concluded that the available information on Chamaecyparis, Cryptomeria and Juniperus suggested that they would not suffer from pine wilt disease and would not act as efficient hosts of the pine wood nematode. However, the experts again highlighted the lack of data concerning the nematode-beetle-plant interaction, which made it difficult to make firm statements about the risk.

The Panel called for further research – particularly on the association between the pine wood nematode, its vector beetles and Chamaecyparis, Cryptomeria, Juniperus and P. pinea plants – and suggested that studies be carried out on the ability of the nematode to survive in field-grown trees that have been inoculated against the pest.

[1] The European Commission requires Member States to take measures against coniferous plants considered to be susceptible to the nematode, and which might support its spread through the movement of infested plants or untreated plant products.
[2] P. pinea is cultivated extensively for its edible nuts. Its wood is used for light construction timber, containers, and as mechanical pulp for cellulose and paper. The bark can be used in plant growth media and the cones can be commercialised for mulches for plant nurseries. P. pinea is also cultivated widely as an ornamental plant and for soil conservation and protection of coastal agricultural crops. Chamaecyparis and Cryptomeria trees are valued in Europe as ornamentals and garden specimens. Juniperus plants are distributed widely in Europe and the northern hemisphere.

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