The box tree moth (Cydalima perspectalis), a moth native to East Asia, was introduced to Europe in the early 2000s. Since its arrival, this pest has rapidly spread, causing considerable damage to boxwoods and threatening their survival.
The box tree moth is considered a serious threat to the ecosystem and the economy. Boxwoods are important native trees that provide a vital habitat for many species of birds and insects. The disappearance of boxwoods due to the moth can lead to ecological imbalance and loss of biodiversity. In addition, the damage caused by the moth can lead to significant costs for nurserymen, landscapers, and garden owners.
Faced with this threat, biological solutions offer an ecological and sustainable alternative to traditional chemical methods. They make it possible to control the box tree moth while minimizing negative impacts on the environment and human health.
Understanding the Box Tree Moth
The box tree moth reproduces several times a year and has a relatively short life cycle, which explains its rapid spread. This pest develops in four stages:
Life Cycle
- Eggs: The moths lay eggs in clusters on the leaves of boxwoods. The eggs are light yellow in color and turn gray-brown before hatching. A female can lay up to 1000 eggs during her lifetime.
- Caterpillars: The caterpillars are light green with black stripes and black dots. They feed voraciously on the leaves, buds, and stems of boxwoods. The caterpillars are particularly active during the day and can cause significant damage in a few weeks.
- Pupae: The caterpillars transform into pupae in silken cocoons that they weave on the leaves or stems of boxwoods. The pupa remains motionless for about two weeks.
- Moths: Adult moths are beige to brown in color with black-flecked wings. The moths are active at night and reproduce rapidly.
Signs of Infestation
Several signs can help detect a box tree moth infestation:
- Presence of webs: The caterpillars of the moth weave webs on the boxwoods to protect themselves and move around. These webs are visible and can be a sign of a significant infestation.
- Visible damage to leaves: The caterpillars of the moth feed on the leaves, causing holes and partial or total defoliation. Infested boxwoods can lose much of their foliage in a few weeks. Affected boxwoods may also have whitish or brownish leaves.
- Visible caterpillars: The caterpillars of the moth are generally visible on the boxwoods, especially during the day. It is possible to observe them moving on the leaves or feeding.
Impacts
The box tree moth has significant impacts on the environment and the economy. In France, it is estimated that 80% of boxwoods have been infested by the box tree moth.
- Disappearance of boxwoods: Boxwoods infested by the moth can lose their foliage and die in a few years. The disappearance of boxwoods can have a significant impact on the ecosystem and lead to a loss of biodiversity.
- Disturbance of the ecosystem: The disappearance of boxwoods can have a significant impact on the ecosystem in general, as they provide a vital habitat for many species of birds and insects.
- Economic loss: Nurserymen, landscapers, and garden owners are heavily affected by the box tree moth. The damage caused by the moth can lead to significant costs for the production, maintenance, and replanting of boxwoods.
Biological Solutions: A Range of Options
Biological solutions offer an ecological and sustainable alternative to traditional chemical pesticides. They make it possible to control the box tree moth by relying on natural processes and minimizing negative impacts on the environment and human health.
Natural Enemies
Nature offers a multitude of natural enemies that can help regulate populations of the box tree moth.
Predatory Insects
- Parasitoid wasps: These wasps lay their eggs inside the caterpillars of the box tree moth. The larvae of the wasp feed on the caterpillar, gradually killing it. In France, the species Cotesia glomerata is particularly effective in controlling the box tree moth. This wasp was introduced to France in 2012 and has helped slow the spread of the moth.
- Ladybugs: Some species of ladybugs feed on eggs and caterpillars of the box tree moth. The seven-spot ladybug (Coccinella septempunctata), a common species in Europe, can consume a large number of caterpillars. The Asian ladybug (Harmonia axyridis), introduced to Europe to control aphids, can also contribute to the control of the box tree moth, but it is also considered an invasive species.
- Hoverflies (Syrphids): Hoverflies are flies that resemble wasps, but are completely harmless. The larvae of hoverflies feed on aphids and can also consume eggs and caterpillars of the box tree moth.
The production and use of predatory insects have become a viable alternative to chemical pesticides. It is possible to buy parasitoid wasps and ladybugs in specialized stores or from companies specializing in biological control. The introduction of predatory insects into gardens is an effective and sustainable practice for regulating populations of the box tree moth.
Insectivorous Birds
Insectivorous birds play an important role in regulating populations of the box tree moth. Studies have shown that species such as the great tit (Parus major), the European robin (Erithacus rubecula), and the Eurasian wren (Troglodytes troglodytes) consume caterpillars of the box tree moth.
To encourage the presence of insectivorous birds in gardens, it is important to create favorable habitats:
- Plant native trees and shrubs: Native trees and shrubs offer nesting sites and food sources for birds.
- Install birdhouses: Birdhouses can provide additional nesting sites for birds.
- Create water sources: Birds need water to drink and bathe. Installing a water source in the garden, such as a bird bath or a small fountain, can attract birds.
Traps
Traps are an effective way to capture adult moths and limit their reproduction.
Pheromone Traps
- How they work: Pheromone traps contain chemical substances that mimic the sex pheromones of females, attracting males. The traps are usually equipped with a sticky container that captures the moths.
- Advantages: Pheromone traps are an effective and selective way to capture male moths, thus reducing the chances of reproduction.
- Selection: There are different types of pheromones, adapted to different regions and times of the year. It is important to choose the appropriate pheromones for the geographic area.
- Placement: Optimal placement of traps is crucial to maximize their effectiveness. Traps should be placed in strategic locations where moths are likely to pass. It is recommended to place the traps near infested boxwoods.
Light Traps
- How they work: Light traps attract nocturnal moths, including the box tree moth. Light traps are usually equipped with a UV light that attracts moths, which are then captured in a sticky container.
- Effectiveness: Light traps can be effective in capturing a large number of moths. However, they can also attract other nocturnal insects, which can have an impact on biodiversity.
- Wavelength: The wavelength of the light emitted by light traps is important to maximize their attractiveness to the box tree moth. Light traps should emit a UV light that is particularly attractive to moths.
Biological Products
Biological products based on natural agents are available to combat the box tree moth.
Bacillus thuringiensis (Bt)
- Mode of action: The bacterium Bacillus thuringiensis (Bt) produces a toxin that paralyzes the digestive system of caterpillars, preventing them from feeding. Bt is effective against a large number of pests, including the box tree moth.
- Formulations: Bt is available in different formulations (powders, suspensions) and can be applied to boxwoods. Powder formulations are generally easier to apply, while suspensions may be more effective at covering boxwoods.
- Responsible use: The use of Bt must be responsible to minimize impacts on the environment and other organisms. It is important to follow the manufacturer's instructions and not apply Bt in excess.
Vegetable Oils
- Mode of action: Vegetable oils, such as neem oil, act by blocking the respiratory pores of caterpillars, suffocating them. Vegetable oils can also have a repellent effect on adult moths.
- Choice and use: It is important to choose vegetable oils that are certified organic and non-toxic to the environment and other organisms. Vegetable oils should be applied with caution, avoiding overuse.
- Effects: Vegetable oils can have negative effects on plants and insects. It is important to test vegetable oils on a small part of the boxwoods before applying them to the entire plant. It is also recommended not to use vegetable oils during the flowering of boxwoods.
Prevention
Prevention is essential to limit infestations of the box tree moth. There are several measures that individuals and professionals can take to minimize the risk of infestation.
Choice of Resistant Varieties
- Resistant varieties: Some varieties of boxwood are more resistant to the box tree moth, such as Buxus microphylla 'Faulkner'. These varieties are generally less vulnerable to moth attacks and can better withstand damage.
- Role of nurseries: Nurseries play an important role in the production and marketing of resistant varieties. It is important to choose boxwoods from reputable nurseries that offer varieties resistant to the box tree moth.
Maintenance and Monitoring
- Pruning: Regular pruning of boxwoods improves ventilation and light penetration. This reduces the risk of infestation because moth caterpillars prefer dense, shady boxwoods.
- Monitoring: Regular monitoring of boxwoods makes it possible to detect the first signs of infestation and take early action. It is important to regularly check boxwoods for the presence of webs, caterpillars, or damage to the leaves.
- Elimination: It is important to remove infested leaves and caterpillars to limit the spread of the box tree moth. The infested leaves and caterpillars must be burned or placed in a tightly closed trash bag to prevent them from dispersing.
Promote Biodiversity
- Create favorable habitats: Plant native trees and shrubs to attract natural predators of the box tree moth. Native trees and shrubs provide habitat and a food source for birds and insect predators of the moth.
- Diversify plantings: Diversify plantings to create a more resilient ecosystem that is less vulnerable to pests. The introduction of varied plants maintains a natural balance and reduces the concentration of the box tree moth.
Biological Solutions: Advantages and Limitations
Biological solutions for controlling the box tree moth have many advantages, but they also have some limitations.
Advantages
- Environmentally friendly: Biological solutions are generally less harmful to the environment than chemical pesticides. They do not pollute the soil, water, and air.
- Non-toxic to humans and animals: Biological solutions are generally non-toxic to humans and animals, which is important for the safety of people and pets.
- Long-term protection: Biological solutions help maintain a natural balance in the ecosystem and prevent future infestations. They are not a temporary solution, but a long-term approach to controlling the box tree moth.
- Sustainable and economical in the long term: Biological solutions are often more economical in the long term than chemical pesticides. The initial cost may be higher, but biological solutions do not require regular applications and are generally more effective in the long term.
Limitations
- Slower effectiveness: Biological solutions may take longer to show their effects than chemical pesticides. It is important to note that biological solutions act gradually and do not provide an immediate solution.
- Requires monitoring and regular application: Biological solutions require monitoring and regular application to maintain their effectiveness. It is important to regularly check boxwoods for the presence of the box tree moth and apply biological solutions as needed.
- Higher initial cost: The initial cost of biological solutions may be higher than that of chemical pesticides. However, biological solutions are often more economical in the long term because they do not require regular applications.
- Not always effective against massive infestations: Biological solutions may not be as effective against massive infestations of the box tree moth. In some cases, it may be necessary to combine biological solutions with other control methods, such as pruning or removing infested leaves and caterpillars.
The Role of Institutions and Individuals
Controlling the box tree moth requires collaboration between institutions and individuals.
- Research programs: Research institutions are developing new biological solutions and improving existing methods. Research is essential to understand the box tree moth, its life cycle, and its modes of spread.
- Public awareness: It is important to raise public awareness of the dangers of the box tree moth and the benefits of biological solutions. The dissemination of information and public awareness are essential to encourage the adoption of ecological and sustainable control methods.
- Citizen initiatives: Individuals can get involved in the fight against the box tree moth by applying biological solutions in their gardens and participating in citizen initiatives. Individual actions have a collective impact and can help slow the spread of the box tree moth.
The protection of the environment and the preservation of biodiversity require collective efforts. The use of biological solutions to control the box tree moth is an important choice to protect boxwoods and the balance of the ecosystem. By adopting environmentally friendly practices, we can contribute to the preservation of biodiversity and the fight against invasive species.