Cheng nematode

The Cheng nematode Bursaphelenchus chengi is a microscopic worm belonging to the order Aphelenchida, family Aphelenchoididae. It is a dangerous wood-inhabiting endoparasite, morphologically related to the notorious pine wilt nematode.

Adult individuals have a thread-like body approximately 0.6–0.8 mm long. To identify the species, specialists use molecular genetic analysis (PCR) and detailed microscopy of the reproductive organs, as they are visually similar to other related species.

The main vectors of this nematode are longhorn beetles of the genus Monochamus. Nematodes enter the beetle's body at the larval stage and move into the trachea, using the insects to disperse between weakened or healthy trees.

The pest's life cycle is closely linked to the developmental phases of the beetle vector. Nematodes actively multiply in the wood, feeding on parenchyma cells and the mycelium of fungi that develop in the tunnels made by beetle larvae.

The spread of the nematode occurs mainly during the warm season when longhorn beetles emerge from infested wood and feed on young conifer shoots, infecting them with the pathogen.

This pest primarily affects coniferous trees, including various species of pine and spruce. The distribution area of the Cheng nematode covers East Asian regions, where it causes significant economic losses in the forestry sector.

The nematode colonizes the tree's vascular tissues, disrupting the flow of water and nutrients. This leads to rapid wilting and the subsequent death of even mature, ostensibly healthy forest stands.

The damage manifests by blocking resin canals, causing the tree to cease resin production. This leaves the plant defenseless against secondary pests, such as bark beetles, which ultimately finish off the weakened tree.

Infested trees lose their ornamental properties and the commercial value of their wood. In forest environments, mass outbreaks of the nematode can lead to local epidemics, causing the death of large forest areas in just one or two seasons.

Young plantations and nurseries are at particular risk, as plant immunity is lower and high planting density facilitates the rapid transmission of the parasite from tree to tree via vectors.

The first visual sign of infestation is a sudden change in needle color, turning yellow and then brown. The yellowing process is rapid, covering the entire tree within a few weeks.

A cessation of resin flow on the trunk is observed. In the areas where beetle exit holes are present, resin flow is completely absent, which can be identified by a careful inspection of the tree bark.

The wood of infested trees often has a specific bluish tint due to the development of associated fungal infections that nematodes carry into the tree tissues. This is confirmed by a cross-section of the trunk.

In dry weather, wilting occurs faster. If a branch of an infested tree is broken, one can notice its dryness and brittleness, as well as the lack of the luster and elasticity typical of healthy needles.

The presence of longhorn beetles on the site, emerging from the wood with characteristic round or oval flight holes, is an indirect but important signal of a potential nematode infestation.

The primary control measure is sanitary logging and the immediate destruction of infested trees. The wood must be burned or fumigated to prevent further spread of the nematodes and their insect vectors.

The use of insecticides against adult longhorn beetles during their active flight period allows for a reduction in the risk of infecting healthy stands. Treatments are applied to tree canopies using systemic and contact-acting products.

It is crucial to restrict the movement of wood products from quarantine zones to safe areas. All export and import timber must undergo mandatory phytosanitary certification and heat treatment.

Maintaining high agronomic standards in forest cultures, including regular fertilization and watering, is recommended, as stressed trees are the most vulnerable to the nematode.

• Regular monitoring of forest areas.
• Removal of deadwood and fallen debris.
• Use of pheromone traps to capture longhorn beetles.
• Biological control using entomopathogenic fungi.