English name: Pine Wood Nematode (PWN), Pine wilt disease
Nordic names: Fyrrevednematod (DK), Mäntyankeroinen(FI), Furuvednematod (NO), Tallvednematod (SE)
Estonian name: Männi-laguuss
Major host plants
B. xylophilus is found mainly on Pinus spp. Other susceptible plants are Abies, Cedrus, Larix, Picea, Pseudotsuga and Tsuga. Reports of damage on other plant species than Pinus are rare. Dead wood of all conifer species (except Thuja) can act as a substrate for the development of B. xylophilus.
Several of the Monochamus spp. are either known or possible vectors of B. xylophilus. They mainly develop in Pinus spp. but other coniferous genera can also act as hosts.
Symptoms usually become evident in late spring or summer. The first indication of the presence of nematodes in the tree is a reduction of oleoresin production. The resin canal cells are destroyed, the tree's water-moving system becomes clogged and resin flow stops.
The first obvious external symptom is the yellowing and wilting of the needles, eventually leading to death of the tree after 30-40 days. The wilting may appear on only one branch although the whole tree may later show symptoms.
Symptomless infestations occur in cold climates when summer temperatures are low (below 20oC). Such infections can remain latent for considerable periods of time and probably forever.
The longhorn beetles only oviposit on recently felled trees and in nearly dead or highly stressed trees. The feeding of the larvae results in bore tunnels and timber degradation.
See pictures on EPPO's website
It is presumed that B. xylophilus originates in North America and was transported from there to Japan in infested timber. From Japan, B. xylophilus has spread to other Asian countries.
In Europe, the nematode was detected in 1999 in Portugal where it now is widely spread and presents a major threat to the rest of Europe.
The different species of Monochamus are widespread in the northern hemisphere.
A map can be downloaded from EPPO’s website. See instructions here.
B. xylophilus has two different life cycle modes. In its propagative life cycle, nematode larvae are transmitted to recently dead or dying trees during oviposition by the female vector. The nematodes enter the tree through a slit in the bark cut by the beetle. Within the wood, the nematodes feed on the hyphae of blue-stain fungi, and the nematode population multiplies rapidly. In the other dispersal mode, the nematode larvae gather in the wood surrounding the pupal chambers of the Monochamus vector. Fungal hyphae also develop around the pupation chambers. This fungus forms long-necked perithecia into the chamber, and the nematodes gather at the tips of the perithecia. When the young adult beetle emerges from the pupa, it brushes against the perithecial necks, picking up the nematodes which enter the beetle. As many as 100.000 larvae may enter a single beetle. The beetle then flies from the wood to healthy pines, where it introduces the nematodes into feeding wounds.
Monochamus beetles emerge through circular exit holes from spring to fall. The immature adult beetles feed on fresh thin bark on living trees, and then they mate and begin to lay eggs in the bark of dying or recently dead conifers. A single female lays up to 100 eggs during a two month period. The eggs hatch within 4 to 12 days depending on the temperature. The larva feeds under the bark and later it bores tunnels in the wood. At the end of these tunnels the larva constructs a pupal chamber. The whole life cycle can be completed within one year, but normally it takes two years.
Pine wood nematode can spread via two different ways:
- Local dispersal by the insect vector Monochamus spp.
- World trade of wood products such as timber, wood chips and wood packing material etc. plays an important role in the potential spread of the pine wood nematode, especially if the wood is infested by the vector beetles too. The nematodes can move actively from infected material and invade wood which contains a vector.
Detection and inspection
Imported wood damaged by longhorn beetles should be sampled if there is any risk of infection. Nematodes are extracted from samples of chipped wood. Identification is done in the laboratory. Pine trees that rapidly wilt should be inspected.
Oval-shaped larval entrance holes and circular exit holes in the wood are characteristic. The galleries and tunnels are filled with frass from larval activity.
Pest status and importance
The pine wood nematode is a major forest pest in the Far East, and also in Portugal despite enormous eradication efforts. Once the nematodes are established, both large areas of pine forests and international wood trade are threatened. Heat treatment of wood is the only effective method to prevent further spread.
Source of information
See further information here:
Author: Christiane Scheel
Editor: Dorthe Vestergaard