Predicting the spread of the most threatening invasive pest for European coniferous forests


A recently published article co-authored by Begoña de la Fuente of the Technical University of Madrid (and visiting scientist at the JRC in 2016-2017), and Santiago Saura and Pieter Beck of the JRC, describes a new model for predicting the spread of the pine wood nematode (PWN), one of the most harmful pests for EU forests, and therefore regulated as a "quarantine pest" under EU law.

Dying pine trees with red and brown leaves as a result of the pine wilt disease caused by the pine wood nematode. © www.rephrame.eu

A microscopic worm originally from North America, it can reproduce rapidly in the wood of most European pine trees, blocking their sap flow which causes the leaves to turn brown, and ultimately kills the tree.

The PWN was first detected in Europe in 1999 in south-western Portugal.

Thanks to its symbiosis with Monochamus galloprovincialis, a flying beetle native to Europe, it has since spread to more than 30% of the country, and caused extensive damage to Portugal’s coniferous forests, which are made up largely of maritime pine trees.

Furthermore, the PWN has been detected in four areas in Spain, three of which it has been eradicated from through EU measures.

Portuguese authorities are implementing the EU Decision to contain the outbreak area and keep a 20-km-wide buffer zone along Portugal's entire mainland border with Spain free from the pine wood nematode.

This includes identifying and removing all coniferous trees in poor health in this ca. 2 million ha area, as they might attract beetles carrying the pest.

As the nematode continues to spread in Portugal, the pressure on this buffer zone is likely to increase.

Tools for forecasting what will happen next could thus help the authorities to plan and prioritize actions and control measures on the ground.

The new study describes a network-based model that simulates the natural spread of the PWN based on the flight behaviour of the Monochamus beetles, and by accounting for all disease infection pathways and sources.

When initiated from the first detection site in Portugal in 1999, the model reproduces the yearly spread of the PWN remarkably well.

Besides capturing the natural spread of the pest, and hence forecasting where and when PWN invasions are more likely to occur in Portugal and Spain in the coming years, the model can also be used to simulate the effect of certain management measures.

For example, simulations indicate that by the year 2006, clear-cut belts could only have stopped the spread if they had been wider than 30 km, as thinner belts merely delayed the invasion.

In contrast, mass trapping of the vector beetle combined with the early detection and removal of infected trees in adjacent areas emerged as more viable control strategies from the simulations.

The authors found that, unless effective containment measures are put in place, the PWN could spread naturally to Spain in about 5 years.

In less than 10 years, it may reach the major forest corridors that provide a gateway for subsequent expansion towards the rest of the Iberian Peninsula and, in the longer term, towards other European countries.

The new model can help management, surveillance, prevention, and treatment efforts by forecasting when areas are at highest risk of invasion by the pine wood nematode and the effects of specific control measures.

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