The Great Capricorn Beetle (Cerambyx cerdo) is a xylophagous insect that feeds on wood. Its larvae, whitish in color and reaching up to 5 cm in length, dig galleries in trees, weakening their structure and potentially leading to their death. This beetle, recognizable by its imposing size (up to 5 cm long) and its long antennae, represents a significant threat to the health of trees in France.
Biology and Life Cycle of the Great Capricorn Beetle
The life cycle of the Great Capricorn Beetle is relatively long, possibly extending over several years. It unfolds in several well-defined stages:
Complete Life Cycle
- Laying eggs: The female Capricorn lays her eggs in the cracks or wounds of the wood, favoring weakened or senescent trees.
- Hatching: The eggs hatch after a few weeks, giving rise to larvae.
- Larval development: The larvae feed on wood, digging deep galleries in the trunk and branches. This stage can last from 2 to 4 years, depending on climatic conditions.
- Pupation: After their larval development, the larvae transform into pupae in a lodge arranged in the wood. This stage usually lasts a few weeks.
- Emergence of the adult: The adult emerges from the wood by digging a characteristic emergence hole, leaving traces of sawdust at the foot of the tree. The adults live for a few weeks and reproduce, ensuring the sustainability of the species.
Duration of the Life Cycle and Number of Generations
The life cycle of the Great Capricorn Beetle lasts on average 3 years, but can reach 5 years in some cases. The duration of the life cycle is influenced by factors such as temperature and food availability. In France, we generally observe only one generation per year.
Early Signs of a Great Capricorn Beetle Infestation
Early detection of a Great Capricorn Beetle infestation is essential to limit damage and implement appropriate treatment solutions. There are several visual and indirect signs that can alert to the presence of this harmful insect.
Visual Signs
- Emergence holes: Circular holes, with a diameter of 1 to 2 cm, are often visible on the trunk or branches of infested trees. These holes are created by adults when they emerge from the wood.
- Sawdust at the foot of the tree: The presence of fine and powdery sawdust at the foot of the tree may indicate larval activity inside the wood.
- Galleries in the wood: Galleries dug by larvae can be seen on exposed wood. They are often irregular and sinuous in shape.
- Deformations of the trunk: The trunk of the tree may show deformations or hollows related to the presence of larval galleries.
- Yellowing and falling leaves: Premature yellowing of the leaves and their fall may be a sign of weakening of the tree due to Great Capricorn Beetle infestation.
Indirect Signs
- Presence of adult capricorn beetles: Observing adult capricorn beetles flying around trees or feeding on flowers is a clear sign of infestation.
- "Gnawing" noises: By listening carefully, it is possible to perceive "gnawing" noises coming from inside the wood. These noises are characteristic of the activity of larvae digging galleries.
Methods for Detecting the Great Capricorn Beetle
To ensure rapid and effective intervention, it is essential to deploy reliable detection methods. Visual methods remain the first step, but other more advanced techniques are available for precise identification.
Visual Methods
- Careful visual inspection: Carefully examine trees, especially the trunk, branches, and leaves, for signs of infestation.
- Use of magnifying glasses or binoculars: To facilitate the observation of emergence holes, galleries or larvae, it is recommended to use magnifying glasses or binoculars.
Acoustic Methods
- Use of microphones: Sensitive microphones can be used to detect the sounds of the larva feeding in the wood.
- Recording mating sounds: Adult capricorn beetles emit characteristic mating sounds. Recording these sounds can be used to identify their presence.
Olfactory Methods
- Pheromone traps: Pheromone traps are used to attract adult capricorn beetles and confirm their presence. Pheromones are chemical substances that mimic the sexual pheromones of females, attracting males.
Imaging Methods
- 3D scanners and thermographic imaging: These technologies can detect galleries inside the wood, even if they are not visible to the naked eye.
- Tomography: Tomography is a non-destructive imaging technique that uses sound waves or X-rays to analyze the internal structures of trees and identify infested areas.
Early Treatment: Interventions and Solutions
As soon as an infestation is detected, it is crucial to act quickly to limit damage and protect trees. Preventive and curative treatments can be put in place, each with its specificities and advantages.
Preventive Solutions
- Promote tree health: Regular watering, fertilization, adapted pruning and removal of dead or weakened branches.
- Remove dead or weakened trees: Eliminate dead trees or those showing signs of weakness because they are more vulnerable to Great Capricorn Beetle infestations.
- Preventive treatment of healthy trees: Apply appropriate insecticides to healthy trees to prevent infestations.
Curative Solutions
Chemical Treatments
- Injection of insecticides: Insecticides are injected into the galleries dug by the larvae to kill them.
- Spraying of insecticide products: Apply insecticide products to the trunk of the tree to fight against adults and larvae.
Biological Treatments
- Entomopathogenic nematodes: These microscopic worms parasitize the larvae of the Great Capricorn Beetle and kill them. They are usually injected into the galleries.
- Natural parasites: Some natural parasites, such as parasitic wasps, can help regulate the population of Great Capricorn Beetles.
Physical Treatments
- Injection of resin or mastic: Introduce resin or mastic into the galleries to prevent the larvae from developing.
- Microwave application: Microwaves can be used to kill larvae in wood.
- Ultrasound devices: Ultrasound devices can be used to repel adults.
Alternative Solutions
- Light traps: Attract adults using light traps.
- Pheromone traps: Attract adults using pheromone traps to prevent them from reproducing.
- Nets: Install nets around trees to prevent females from laying their eggs in the wood.
Special Cases and Practical Advice
Managing infested trees and preventing Great Capricorn Beetle infestations requires a personalized approach based on the situation. Here are some practical tips and solutions adapted to specific cases.
Management of Infested Trees
- Felling and destruction of infested wood: In severe cases, felling the infested tree and destroying the wood is necessary to prevent the spread of the insect.
- Heat treatment of infested wood: The infested wood can be heat-treated to kill the larvae and adults.
- Use of wood for uses not sensitive to infestation: The infested wood can be used for uses not sensitive to infestation, such as the manufacture of furniture or frames, after adequate treatment.
Legislation and Regulations
French legislation imposes obligations on owners of trees infested by the Great Capricorn Beetle. It is important to inquire about the administrative procedures to be carried out in case of infestation.
Tips for Managing Trees in High-Risk Areas
- Regular inspection of trees: Regularly inspect trees, especially those that are old or weakened, to detect signs of infestation.
- Increased monitoring of at-risk trees: Pay particular attention to trees located in areas where the Great Capricorn Beetle is present.
- Use of appropriate products: Apply appropriate products to protect trees and prevent the spread of the insect.
Prevention is the best weapon against the Great Capricorn Beetle. By following practical advice and implementing appropriate treatment solutions, tree owners can contribute to the protection of trees and the preservation of biodiversity.