Box tree moth: life cycle, identification & treatment

Box tree moth: life cycle, identification & treatment

Learn everything you need to know in order to recognise and treat an infestation by the voracious box tree moth and its caterpillars here.

Have you noticed any discoloured leaves, dead branches, white webs and caterpillars on your box tree (Buxus) – or observed these symptoms in the neighbourhood? These signs very possibly point to an infestation of the infamous box tree moth (Cydalima perspectalis). Now is the time to inform yourself and act fast in order to minimize the damage on your shrubs.

Box tree moth

The box tree moth is an invasive species from East Asia. It was introduced to Central Europe a few years ago and it specializes in box trees, which in many areas led to a complete devastation of these evergreen shrubs. This article will give you a brief overview of the box tree moth: around which time of the year the box tree moth is active, how it can be recognised and how to effectively treat it whether it be chemically or naturally.

Box tree moth: a life cycle in a year

The problem with the box tree moth is that it leads a rather hidden existence. The moths are nocturnal, so the laying of the eggs happens unnoticed – unless you use a pheromone trap. Directly below this paragraph, you can see a table which shows the development of the moth in the course of the year. Unfortunately, this is not an all-encompassing representation because the speed of larval development is temperature-dependent, among other things. A very mild spring can cause a delay in the development of several weeks. The observation of the moth flight with traps and the regular control of the shrubs between March and September is therefore unfortunately the only possible and reliable way to notice the start of an outbreak in time.

Developmental stageCaterpillars (overwinter)CocoonsMoths, eggsEggs, caterpillarsCocoons, mothsMoths, caterpillars, eggs
GenerationLast year's generationGeneration 1Generation 2

How to recognise the box tree moth

Fortunately, it is possible to detect the moth long before the dead yellow branches appear on the shrub. The yellowish eggs are located in the outer areas of the box tree in densely packed formations. The larvae, that are just a few millimetres in size, hatch from those eggs. They are light green-yellow in colour and have a typical black head. Immediately after hatching, they make their way to the protected interior of the shrub to hide in webs and eat the poisonous boxwood leaves. After the larvae have grown a little bigger and have several moults behind them, the colour of the caterpillars changes. They become a little darker and the characteristic black and white pattern emerges. At this point, they leave the interior of the box tree and return to the exterior. After the six larval stages, the pupation, which occurs also in the hidden webs, follows. As a result, the caterpillars transform into moths. The adult moth is usually brightly coloured. It will produce the next generation of ravenous caterpillars.

box caterpillar
Caterpillars of box tree moths are green and yellow and have a characteristic black head [ SanderMeertinsPhotography]

We have created detailed articles with pictures for you, which describe the eggs and the caterpillars of the box tree moth in detail. However, if you suspect another disease of your box tree, here is a comprehensive guide to other diseases of Buxus.

Summary of how to recognise the box tree moth:

  • Severe infestation leads to the branch parts dying off
  • You can recognise an infestation earlier by the webs and the max. 5 cm long caterpillars; the caterpillars are green-yellow, later with black-and-white markings and white bristles; they have a characteristic black head
  • The eggs are yellowish and are deposited in the outer shrub areas, under the leaves
  • The approximately 4.5 cm long butterflies are not always the same colour but they are usually bright with black wing edges

Getting rid of box tree moths

If you have recognised the infestation early or if it is still small, we recommend reading this article on effective household remedies. It describes various interesting effective methods – such as using a strong jet of water from a garden hose – and less effective approaches – such as baking powder or algae lime. However, if your situation is more severe and you are dealing with a rapidly dying box tree full of caterpillars, then your approach has to be different. You need to make up your mind: are you looking for alternatives for the box tree or is your goal to eliminate the caterpillars? You can find out how to get rid of the box tree moth here. If you are not interested in treating the caterpillars with poison, you can find natural methods that achieve good results without chemicals. The use of nematodes, neem oil and preparations with Bacillus thuringiensis work amazingly and yet they are gentle to the environment. Insecticides are often effective, but they can harm important beneficial animals in the garden, which could only worsen the pest problems in the long run.

Tip: You don’t have to be afraid of touching the box tree caterpillars. The caterpillars are not harmful to the skin. But you should not eat them – and wash your hands diligently after handling them. The animals contain several toxic compounds which they absorb from the poisonous box tree. You can learn more about the poisonous nature of the moth here.

When is the best time to treat the box tree moth?

Note the following: the right time of treatment is essential for the success. For example, applying a spray onto the caterpillars when they are still wrapped in leaves, will have no effect whatsoever. The same goes for the boxwood eggs and cocoons. You might be asking, when you should use the spray or other remedies to treat the moth? This article will explain when the perfect time to treat the box tree moth is.

Natural control of box tree moths with XenTari

If you are looking for an effective, simple and yet environmentally friendly method of control, we recommend choosing a product with the active ingedient XenTari. These products are often used in organic farming because they tend to have less negative effects on beneficial humans and humans.

The active ingredient contained in many natural product is the spores of a specialized bacterium with high endurance, Bacillus thuringiensis. If they are applied to the leaves of the infested plant, they are absorbed by the caterpillars as they feed. In the caterpillar’s intestine, the bacteria release a toxin which hinders further feeding and thus causes the box caterpillars to perish in around five days. We recommend such sprays because they specifically target the box tree moth, are safer for users and tent to have better results that commercial insecticides.

Tip: You can also use products with XenTari as the active ingredient to treat the caterpillars on fruit trees and cabbages – such products work well with cabbage pests Evergestis forficalis and coddling moths that infest apple trees.

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