Bursaphelenchus xylophilus
, the pinewood nematode (PWN) and causal agent of Pine Wilt Disease (PWD), was detected for the first time, in 1999, in Portugal, and in Europe. Despite the efforts of the ...Portuguese National Forestry and Quarantine Authorities, the disease has spread to new forest areas in the centre of mainland Portugal, in 2008, and to the island of Madeira, in 2009. More recently, two foci of PWD were reported from Spain. The free circulation of non-treated wood and wood products, as part of global trade, may explain this phenomenon, which constitutes a threat to other European forestlands. This review gathers the most recent up-to-date information about PWD in Europe, as well as in other countries, presenting integrative management procedures for detection and control, and the scientific knowledge generated over the last decade, to understand the complex biological system behind the disease.
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•An individual-based dispersal model was developed for flying pine sawyers.•This model was parameterized with flight mill and mark-release-recapture data.•According to simulations, ...beetles could fly on average 63 km in total.•Clear-cut zones of 500 m could not prevent the spread of the pine wood nematode.
The number of invasive species is increasing throughout the world. One of the corner stones to successfully control them is to better estimate their dispersal capabilities. For flying insects, dispersal performance is commonly estimated through flight mill and mark-release-recapture experiments. However, each approach has its own bias, over- and under-estimating flying distances respectively. The objective of this study was to develop an individual-based dispersal model to circumvent these drawbacks. The shape of the dispersal kernel was calibrated on distances recorded in flight mill experiments (previously done) and then model parameters were fine-tuned based on mark-release-recapture experiments (presented in this study). The pine sawyer beetle, Monochamus galloprovincialis, was used as case study because it is the European vector of the invasive pine wood nematode, Bursaphelenchus xylophilus, recognized as one of the biggest threats to pine forests worldwide. The best fitted model to mark-release-recapture data was parameterized with a mean flying distance of 2000 m per day, which is consistent with flight mill data. It was used to further simulate the dispersal of 100 beetles in non-fragmented pine forests. The cumulative flight distance was 63 km on average at the end of their adult life stage, and the mean dispersal distance as the crow flies was of ca. 13 km. At the end of the maturation period, when most nematodes have been already transmitted to host pines via shoot feeding, about 80% of the insects were located at more than 500 m from the emergence point. These outcomes clearly question the relevance of clear-cut zones of 500 m radius required by the European regulation for the eradication of the invasive nematode. Such dispersal model could be used to support decision-making for eradication programs.
1. Invasive tree pests are increasingly threatening forest ecosystems. Understanding and controlling their spread presents a major challenge for managers, researchers, and policy makers. In 1999, the ...pine wood nematode (PWN) Bursaphelenchus xylophilus, causal agent of pine wilt disease and native to North America, was first detected in Europe, more precisely in south-western Portugal. Since then, it has spread to more than 30% of the country, producing large-scale damages in Portuguese forests. 2. We applied a new spatio-temporal network-based model to predict, at yearly intervals, the natural spread of the PWN on the Iberian Peninsula, as dispersed by the longhorn beetle Monochamus galloprovinaalis, its only known vector in Europe. We compared the model predictions with independent observations of the natural spread of pine wilt disease in Portugal between 2005 and 2015. We simulated the effect of potential containment measures on the disease spread. 3. The model predicted the status (infected or non-infected) of forest areas with 93% accuracy, had 93% sensitivity and specificity, and AUC = 0.96 (averages for 8 years with validation data). 4. Simulated clear-cut belts stopped the spread only if they were wider than 30 km, although thinner belts delayed invasion. Furthermore, clear-cuts were much more effective in slowing down the invasion when reinforced, in the adjacent areas, by the reduction in the vector beetle population through mass trapping and by the early detection and removal of infected trees. 5. Model projections identified areas through which the nematode is most likely to invade, by natural means, the phytosanitary buffer zone established along the Portuguese border, and Spain. 6. Synthesis and applications. In the absence of effective containment measures, the pine wood nematode may naturally spread into Spain in about 5 years. In less than 10 years, it may reach the major forest and climatic corridors that provide a gateway for subsequent expansion towards the rest of the Iberian Peninsula and, in the longer term, towards other European countries. Our model can considerably support management efforts by forecasting when areas are at highest risk of vector-mediated invasion as well as the effects of specific control measures on the disease spread.
Pine Wilt Disease (PWD) has a significant impact on Eurasia pine forests. The microbiome of the nematode (the primary cause of the disease), its insect vector, and the host tree may be relevant for ...the disease mechanism. The aim of this study was to characterize these microbiomes, from three PWD-affected areas in Portugal, using Denaturing Gradient Gel Electrophoresis, 16S rRNA gene pyrosequencing, and a functional inference-based approach (PICRUSt). The bacterial community structure of the nematode was significantly different from the infected trees but closely related to the insect vector, supporting the hypothesis that the nematode microbiome might be in part inherited from the insect. Sampling location influenced mostly the tree microbiome (P < 0.05). Genes related both with plant growth promotion and phytopathogenicity were predicted for the tree microbiome. Xenobiotic degradation functions were predicted in the nematode and insect microbiomes. Phytotoxin biosynthesis was also predicted for the nematode microbiome, supporting the theory of a direct contribution of the microbiome to tree-wilting. This is the first study that simultaneously characterized the nematode, tree and insect-vector microbiomes from the same affected areas, and overall the results support the hypothesis that the PWD microbiome plays an important role in the disease's development.
The invasive pine wood nematode (PWN) Bursaphelenchus xylophilus is one of the most serious threats to pine forests across the world. Detected in Europe in 1999, it has largely spread despite ...containment measures.
Following the European Union regulations, the requested eradication measure is to fell, remove and dispose of all susceptible plants within a clear‐cut zone (CCZ) of a radius of 500 m around any infected tree. This measure is controversial since its effectiveness is questioned.
An individual‐based model, describing the dispersal of the nematode vector and the nematode transmission, was used to estimate the relationship between the radius and the effectiveness of the CCZ at eradicating the PWN.
Clear‐cutting of a 500‐m radius is poorly effective in non‐fragmented pine forests since it reduces the number of PWN transmissions by only 0.6%–11.5%. To significantly reduce the number of transmissions, the radius should be between 14 and 38 km, which is not technically nor ethically feasible.
Policy implications. Our results, based on model simulations at a fine spatial scale, prove that clear‐cutting susceptible trees 500 m around any infested tree—as requested by EU regulation to eradicate the PWN—is not effective in large and continuous pine forests. Instead, strengthened surveillance and sanitation felling could be explored.
Résumé
Le nématode du pin (PWN), Bursaphelenchus xylophilus, est l'une des plus importantes espèces invasives menaçant les forêts de pins dans le monde. Après avoir été détecté en Europe en 1999, il s'est rapidement propagé au Portugal puis en Espagne, malgré les mesures mises en place pour le contenir.
Selon la réglementation de l’Union Européenne, la mesure relative à l’éradication consiste à abattre, retirer et éliminer tous les végétaux sensibles dans une zone de coupe à blanc (CCZ) d'un rayon de 500 m autour de tout arbre infecté par le PWN. Cette mesure est controversée car son efficacité est incertaine.
Un modèle individu‐centré, décrivant la dispersion de l'insecte vecteur ainsi que la transmission du PWN, a été utilisé pour estimer la relation entre le rayon de la coupe à blanc et son efficacité à éradiquer le PWN.
Une coupe à blanc d‘un rayon de 500 m est très peu efficace dans une forêt de pins non fragmentée car elle ne peut réduire le nombre de transmissions du PWN que de 0.6% à 11.5%. Pour réduire de manière significative ce nombre de transmissions, le rayon devrait être de 14 à 38 km, ce qui n'est de façon évidente pas envisageable d'un point de vue technique ou éthique.
Implications politiques. Nos résultats, issus de simulations conduites à une échelle spatiale fine, prouvent que la coupe des végétaux sensibles dans un rayon de 500 m autour de tout arbre infecté—comme demandée par la réglementation de l’Union Européenne pour éradiquer le nématode du pin—n'est pas efficace dans les grandes forêts de pins non fragmentées. À la place, le renforcement de la surveillance et des coupes sanitaires ciblées devraient être envisagé.
Our results, based on model simulations at a fine spatial scale, prove that clear‐cutting susceptible trees 500 m around any infested tree—as requested by EU regulation to eradicate the pine wood nematode—is not effective in large and continuous pine forests. Instead, strengthened surveillance and sanitation felling could be explored.
was detected in association with the pine sawyer beetle (
) during the implementation and testing of cross traps with insect attractants as an efficient tool for detection survey for pine wood ...nematode (
) in Bosnia and Herzegovina and Georgia in 2017 and 2018, respectively. This nematode was characterized by morphological, morphometric and molecular features. This is the first report of
in association with a
in Bosnia and Herzegovina and in Georgia.
Pheromone traps are widely used for monitoring or managing insect pest populations. However, it is important to know their range of attraction to optimize the setting of pheromone trap networks.
We ...propose an easy method based on the use of pairs of adjacent traps located at decreasing distance from each other. The range of attraction is deduced from the observation of reduced trap capture when the attraction range of two adjacent traps starts overlapping. The relationship between the relative trap capture and the distance between paired traps is fitted with a logistic curve.
To empirically test these predictions, we conducted trapping experiments with the beetle Monochamus galloprovincialis, the insect vector of the pine wood nematode. Fifteen pairs of traps separated by 25 to 300 m, in France, and 18 pairs of traps distant from 25 to 400 m, in Portugal, were installed in maritime pine plantation landscapes.
In both countries, the relative percentage of capture per trap per week was best fitted by a logistic model with two parameters. The estimated attraction ranges were 92 m (confidence interval = 62–211 m) in France and 123 m (confidence interval = 64–491 m) in Portugal.
The interference between paired traps thus provides a simple and robust method for estimating the attraction range of pheromone traps.
Key message
In mixed stands of
Pinus pinaster
and
Pinus pinea
, fewer insect vectors of the pinewood nematode (PWN) were captured than in pure
P. pinaster
stands. This finding has practical ...implications for PWN disease management, including the recommendation to improve the diversity of maritime pine plantations and to conserve stone pines in infected areas.
Context
The PWN is an invasive species in European pine forests, being vectored by the longhorn beetle
Monochamus galloprovincialis
. The presence of less preferred host trees may disrupt the insect vector dispersal and slow the spread of the disease.
Aims
The aim of the study was to compare the abundance of
M. galloprovincialis
in pure stands of
Pinus pinaster
, a preferred host tree, pure
P. pinea
stands, a less preferred host, and mixtures of these two species.
Methods
We selected 20 mature pine stands varying in %
P. pinaster
and %
P. pinea
in Spain. In each stand, we installed 3 pheromone traps to catch
M. galloprovincialis
. We related trap catches to stand and landscape composition.
Results
The level of capture of
M. galloprovincialis
was highest in pure
P. pinaster
stands and decreased with increasing proportion of
P. pinea
.
Conclusions
The presence of stone pine mixed with maritime pine significantly reduces the local abundance of the PWN insect vector. The most plausible mechanism is that
P. pinea
emits odors that have a repulsive effect on dispersing beetles.
Context
The pine wood nematode (PWN) is an invasive species which was introduced into Europe in 1999. It represents a major economic and ecological threat to European forests. In Europe, the maritime ...pine is the main host and
Monochamus galloprovinciallis
is its only vector.
Objectives
Our goal was to analyze the effect of landscape heterogeneity on the vector’s dispersal. We further aimed at developing a new method to locate the origin of insects captured in a systematic network of pheromone traps.
Methods
A mark-release-recapture experiment was carried out in a heterogeneous landscape combining maritime pine plantations, clear-cuts and isolated patches of broadleaved and mixed forests in the southwest of France. Least-cost path analysis was used to model dispersal trajectories and assign friction values to each land-use type in the landscape. We used the trap’s geographical coordinates, capture levels and mean friction values of neighbouring patches to calculate a weighed barycentre and the position of the release of marked beetles.
Results
Least Cost Path modelling revealed the vector’s tendency to avoid habitat patches such as mixed or deciduous forests and not avoid clear-cuts. The weighted barycentre method was greatly improved when the friction values of the trap’s surrounding land-uses were used.
Conclusions
Our study demonstrates the value of applying landscape ecology concepts and methods to improve our understanding and prediction of pest invasion processes. A practical application is the design of systematic grids of pheromone traps to locate the infection focus from which PWN vectors originate in a newly colonized area.
Invasive pests, such as the pine wood nematode (PWN), threaten European forests. In De la Fuente, Saura, and Beck, Journal of Applied Ecology, 2018, 55, 2374, we modelled the natural spread of the ...PWN by the longhorn beetle (Monochamus galloprovincialis) on the Iberian Peninsula. We used the model to evaluate the effectiveness of several management measures to control the PWN spread: early detection and removal of infected trees, beetle mass trapping and clear‐cut belts. We simulated these particular measures because they have been or are being applied in PWN containment efforts on the Iberian Peninsula.
Martínez‐Abraín and Jiménez, Journal of Applied Ecology, 2019, suggested that two other management measures would be appropriate to halt the PWN expansion: installing nest boxes for insectivorous birds in order to increase predation on vector beetles and increasing the populations of large mammalian herbivores to lower forest tree density.
The results of De la Fuente, Saura, and Beck, Journal of Applied Ecology, 2018, 55, 2374 showed that a combination of measures is more likely to control PWN spread than any single one in isolation, indicating that halting this, and many other invasive species, requires a comprehensive approach.
Here, we review current evidence on the efficacy of the measures proposed by Martínez‐Abraín and Jiménez, Journal of Applied Ecology, 2019, as PWN management tools. This evidence suggests that, by themselves, these measures are unlikely to significantly slow down, let alone halt, the PWN spread on the Iberian Peninsula. Furthermore, we indicate how the model presented in De la Fuente, Saura, and Beck, Journal of Applied Ecology, 2018, 55, 2374 lends itself to assessing this quantitatively in future research.
Synthesis and applications. Lost biotic interactions in ecosystems can make them more vulnerable to invasions, and restoring interactions can in turn increase resilience. Ecosystem restoration can thus, in theory, also benefit invasive species management. Current evidence indicates however that managing natural species interactions, such as beetle predation from insectivorous birds or herbivory by large mammals, would need to be applied in combination with other measures if they are to halt or significantly slow down the expansion of the PWN in Europe.
Resumen
Las especies invasoras, y entre ellas el nematodo de la madera del pino, amenazan los bosques europeos. De la Fuente, Saura, and Beck, Journal of Applied Ecology, 2018, 55, 2374 modelizaron la dispersión natural de esta plaga invasora a través de los movimientos realizados por su insecto vector (Monochamus galloprovincialis) en la península ibérica. Aplicaron este modelo para evaluar la efectividad de diferentes medidas para contener su expansión: detección temprana y eliminación de árboles infectados, captura masiva del insecto vector del nematodo, y cortas a hecho de la vegetación vulnerable en franjas de distintas anchuras. Estas medidas son las que se han aplicado o se están aplicando en la península ibérica para intentar contener la propagación del nematodo de la madera del pino.
Martínez‐Abraín y Jiménez, Journal of Applied Ecology, 2019, sugieren que otras dos medidas de gestión podrían ser apropiadas para contener la expansión del nematodo: instalar cajas nido para aves insectívoras con el objeto de aumentar la depredación sobre el insecto vector e incrementar las poblaciones de mamíferos herbívoros para disminuir la densidad del arbolado.
Los resultados obtenidos en De la Fuente et al. (2018) mostraron que una combinación de medidas, en lugar de una sola medida de control, es más efectiva para detener o ralentizar significativamente la propagación de esta plaga, lo que indica la necesidad de estrategias de gestión integradas para hacer frente a esta y otras especies invasoras.
En este artículo revisamos las evidencias actuales sobre la eficacia de las medidas propuestas por Martínez‐Abraín y Jiménez, Journal of Applied Ecology, 2019, como herramientas de gestión para el control de la expansión del nematodo. Estas evidencias sugieren que, por sí mismas, estas medidas no serían capaces de detener ni reducir significativamente la velocidad de dispersión del nematodo de la madera del pino en la península ibérica. También apuntamos cómo el modelo presentado en De la Fuente et al. (2018) podría permitir evaluar cuantitativamente los efectos de estas medidas en futuros estudios.
Síntesis y aplicaciones. La pérdida de interacciones bióticas dentro de los ecosistemas puede provocar que estos sean más vulnerables a los agentes invasores. Restaurar estas interacciones y los ecosistemas forestales en su conjunto puede aumentar la resiliencia de nuestros bosques frente a estas amenazas y, por tanto, favorecer el control de las especies invasoras. Sin embargo, las evidencias disponibles indican que las medidas de gestión para potenciar ciertas interacciones naturales entre las especies, tales como la depredación del insecto vector por aves insectívoras o el ramoneo de la vegetación forestal por grandes herbívoros, serían por sí mismas insuficientes y requerirían ser aplicadas conjuntamente con otras medidas para conseguir frenar la expansión del nematodo de la madera del pino en Europa.
Lost biotic interactions in ecosystems can make them more vulnerable to invasions, and restoring interactions can in turn increase resilience. Ecosystem restoration can thus, in theory, also benefit invasive species management. Current evidence indicates however that managing natural species interactions, such as beetle predation from insectivorous birds or herbivory by large mammals, would need to be applied in combination with other measures if they are to halt or significantly slow down the expansion of the pine wood nematode in Europe.
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