The pinewood nematode: a threat to conifers

The pinewood nematode (Bursaphelenchus xylophilus) is a microscopic worm that infests conifers, particularly those of the genus Pinus, and can lead to wilting of the affected trees. This parasite is therefore closely monitored, especially in the European Union, where it is classified as a priority quarantine organism. In France, an annual monitoring programme for the pinewood nematode has been in place since 2000. An outbreak was detected for the first time on 3 November 2025 in the Landes administrative département, and by March 2026 it had spread over an area of about two kilometres. ANSES is the National and European Reference Laboratory for plant-parasitic nematodes. It also carries out expert appraisals to assess the risks of this pest entering and becoming established in mainland France, and to make recommendations for managing monitoring of the nematode's vector, Monochamus galloprovincialis, via trapping, and for managing felled trees during this insect’s flight period.

What is the pinewood nematode?

The pinewood nematode is a microscopic worm that attacks certain conifers, mainly pine trees. Once inside the trees and when climate conditions are favourable, the nematodes multiply and block the flow of sap. Affected trees turn red, lose their needles and can die within a few weeks. Originally from North America, the pinewood nematode spread to Asia before arriving in Europe. In several regions of the world (Asia, Europe), this particularly destructive parasite has had serious consequences for forests and the related industries. It has been widespread in Portugal since 1999 and has been found in certain areas of Spain since 2008. The first outbreak in France was detected and confirmed on 3 November 2025 in the Landes département. The nematodes are spread from tree to tree via their insect vector, M. galloprovincialis, which is found in all regions of mainland France. This insect can become a carrier when it comes into contact with the nematode during its larval development in a contaminated tree. When the adult insect emerges from this tree, it may be carrying pinewood nematodes and will then transmit them from one tree to another while feeding on sap or laying its eggs.

What is the risk of infestation?

The international spread of the pest is mainly due to the transport of wood or plants. Infested wood packaging and bark were first discovered in France in 1992 and have been found repeatedly since 2000.

The Landes de Gascogne forest is a high-risk area because it has several factors favourable to the parasite's establishment: the presence of the insect vector and a forest area made up of pine species that are susceptible to the nematode, including maritime pines.

The risk of the disease spreading from an outbreak is linked to the ability of the insect vector to transmit the nematode from tree to tree and depends on:

the nature of the products and by-products resulting from forestry exploitation and in particular their dimensions;
the fate of these materials: storage for varying lengths of time and transport;
the period considered: during or outside the insect vector’s flight period.

What measures should be taken if a pinewood nematode outbreak is detected?

If pinewood nematodes are detected, European Union legislation requires mandatory management measures to be taken. These aim to limit the risk of the spread of the pinewood nematode and its insect vector. The French Directorate General for Food and its regional delegations then coordinate the deployment of the national health emergency plan. These measures involve establishing an infested zone with a radius of 500 metres around the contaminated trees, within which all conifers susceptible to the nematode must be felled and removed. In addition, a 20-kilometre buffer zone must be established around the outbreak site, within which management measures are implemented, including a ban on forestry exploitation and timber transport. These measures are combined with active surveillance of susceptible trees in the zone.

ANSES’s role in combating the pinewood nematode

National and European Reference Laboratory

The Nematology Unit of ANSES's Plant Health Laboratory (in Rennes, Ille-et-Vilaine) is the National and European Reference Laboratory for identification of plant-parasitic nematodes such as the pinewood nematode. In this capacity, it has been working for more than 25 years to develop innovative detection methods to ensure enhanced biological monitoring in France and Europe. Every week, the laboratory supervises or conducts tests on wood samples taken from ports, forests or factories, as well as sampling of the insect vector.

Expert appraisals with a view to preventing and managing pinewood nematode outbreaks

Before the first pinewood nematode outbreak in France was discovered in 2025, ANSES had already conducted several expert appraisals to assess the risk of introduction and establishment of this parasite and to recommend wood management measures to be applied in France.

Transport, storage and treatment of wood or bark if an outbreak of this parasite is declared

ANSES assessed the risk of the pinewood nematode spreading during the transport and storage of timber, following a request from Portugal to authorise the export of contaminated wood following the devastating forest fires of 2017.

Species likely to facilitate the multiplication of the pinewood nematode

The Agency also assessed the susceptibility of different plant species to the pinewood nematode. This parasite mainly affects species of the genus Pinus, but also other conifers such as firs and cedars.

Management of pine bark potentially contaminated by the pinewood nematode

In 2018, following the discovery of bark from Portugal contaminated by the pinewood nematode and intended for sale in France, ANSES conducted an expert appraisal on management of the risk posed by pine bark.

Following the first detection in France, ANSES published several opinions to support efforts to combat the pinewood nematode:

Improving the vector trapping strategy for early detection of new outbreaks
In April 2026, the Agency published an expert appraisal on the most appropriate strategy for trapping the insect vector (PDF in French) in order to monitor the pinewood nematode. It recommended prioritising potential entry points for insect vectors infected with the nematode, such as ports, airports, sawmills and nearby wooded areas.

Find out more

Tassus X., Grosdidier M., Hotte H., Jactel H., Kersaudy E., Mariette N., Robinet C., Roux G. 2025. Chapitre 7, L’association entre le nématode du pin invasif et un insecte local menace les forêts françaises. Dans : Invasion et expansion d’insectes bioagresseurs forestiers. Quels risques pour la forêt française dans le contexte des changements globaux ? [Chapter 7, The association between the invasive pinewood nematode and a local insect is threatening French forests. From Invasion and expansion of forest insect pests. What are the risks to French forests in the context of climate change?], published by Quæ, 312p. DOI: 10.35690/978-2-7592-4048-7 [CM1]