Pine nematode detected in France’s forests

This parasite, responsible for devastating losses in countries across the Iberian Peninsula, has been feared by the scientific community for almost 20 years.

Tiny and almost impossible to see with the naked eye, this worm could wipe out vast areas of France’s forests. It particularly targets maritime pine (Pinus pinaster), on which it relies for survival, although it can infect every conifer except thuja. Its name is Bursaphelenchus xylophilus, more commonly known as the pine nematode. On 4 November, the Ministry of Agriculture announced that it had identified the first specimens on French soil, in the municipality of Seignosse (Landes).

The pine nematode is a highly virulent invasive species from North America, now threatening the ecological and economic cornerstone of the Landes forest. Its arrival could jeopardise decades of forest management in an area already weakened by heatwaves and wildfires.

Pine nematode: the new nightmare for French forests

Measuring less than a millimetre long, the pine nematode is nevertheless a voracious pest with an insatiable appetite. It enters the resin-conducting tissues - the tree’s vascular system - and obstructs their flow. Deprived of this essential sap and unable to transport water to its upper branches, the pine dries out, turns yellow and dies within only a few weeks. Its reproductive cycle is also exceptionally brief: during warm periods, in spring and summer, it can be completed in as little as four days.

Unlike other parasitic insects or fungi that attack trees, the nematode leaves almost no visible mark on the bark, making detection even more difficult. It invades the pine from within, initially without any apparent symptoms, before its needles lose their colour and the tree dies standing upright.

How the pine nematode spreads through trees

The parasite is carried by the pine sawyer beetle (Monochamus galloprovincialis), a beetle that feeds on weakened trees. When an adult insect eats bark or lays eggs in a trunk, the nematodes it unwittingly carries on its body or in its respiratory passages enter the wood, where they can then begin their cycle.

When it was first found in Europe in 1999, it destroyed millions of trees in Portugal, forcing the country to launch an emergency reforestation operation. Less than ten years later, in 2008, the nematode crossed into Spain, causing devastation on the same scale. The Pyrenees have evidently not been enough to halt its advance and, now that it has reached the Landes, it will have every opportunity to infest the vast forests for which the region is known.

Why the pine nematode may become endemic in France

Already established in several parts of the world, including Japan, Taiwan and China, France must now be added to the list of affected territories. How did it get there? A combination of factors has encouraged its establishment and spread: milder temperatures linked to climate change, drought, and forestry monoculture practices that undermine forest resilience. Worse still, once the nematode has adapted to an ecosystem, it is almost impossible to eradicate. Only containment measures - preventative tree felling, destruction of cut infected timber and control of insect vectors - can slow its progression; eliminating it altogether is beyond reach. Everything suggests that the nematode will continue to spread through France’s forests, as it has elsewhere, and it is highly likely that the pine nematode will eventually become endemic.