If you want to fight box tree moth caterpillars, you must be able to recognize them for sure. We provide good pictures, descriptions and information for identification.
The caterpillar of the box tree moth (Cydalima perspectalis) has an enormous damage potential and can get through the beloved box tree (Buxus) in a very short time put an end to bald frass. Identifying the pest is important so that you don't accidentally use sprays or other time-consuming methods for no reason - or, conversely, allow a beautiful piece of greenery in the garden to be destroyed.
Know your enemy: what does the caterpillar of the box tree moth look like? When do you meet them and how do the different larval stages live? We answer these important questions and show ways to combat the borer caterpillar.
What does the caterpillar of the box tree moth look like?
Approximately three days after the moth lays its eggs, small, yellowish-green caterpillars with a jet-black head capsule hatch from the box tree moth eggs. This conspicuous black head also distinguishes all upcoming larval stages. After several molts, the caterpillars grow to a maximum length of five centimeters and develop the typical yellow-green coloring with black-and-white markings, black dots and white bristles. They have three pairs of well-moving sternums at the front end and five pairs of ventral legs at the rear end. Pupation after the sixth larval stage occurs in a web in a pupa about two centimeters long, which also has black and white vertical stripes.
When can you find the caterpillar of the box tree moth?
The box tree moth overwinters as a caterpillar in the third or fourth larval stage, spun in a protective cocoon. If the temperatures rise to around 12 °C from mid-March, the caterpillars become active again, eat and continue to develop. Depending on the weather at the beginning of the year, the first caterpillars can be observed as early as March - earlier in warmer springs, in colder oneslater.
After the metamorphosis of these overwintered caterpillars, eggs are laid again around June, so that this year's first generation of box tree moth caterpillars can be found in July. After their complete development, the second and final generation of caterpillars will be in September. It now in turn develops only up to the third or fourth larval stage and then hibernates in a cocoon. The table below shows the development cycle of the box tree moth.
| month | April | May | June | July | August | September |
|---|---|---|---|---|---|---|
| Development State | Caterpillars (overwintered) | Cocoons | Moths, Eggs | Eggs, Caterpillars | Cocoons, moths | Moths, Eggs, Caterpillars |
| Generation | Generation previous year | Generation 1 | Generation 2 | |||
Note: In warmer regions it is possible that in one year instead of two generations there may be three generations of borers. In this case, the development periods differ from those mentioned above. Only by observing the flight of moths using pheromone traps - such as the Plantura moth trap - can reliable predictions be made about the imminent emergence of voracious caterpillars.
Box tree moth caterpillar: Habitat
The caterpillars of the box tree moth have a high damage potential on our box trees due to their many larval stages and the development period of one month. Due to their cryptic, i.e. well-hidden way of life, they often escape hungry birds and human methods of combating them. Young larvae hide inside the boxwood, spun between leaves, and prefer to feed on older leaves with higher concentrations of the boxwood's toxic alkaloids. In this way, the larvae of the box tree moth become poisonous or inedible and spurned by most predators. Living in fine webs underneath the leaves and the coloring of the caterpillars mean considerable protection. Older caterpillars also venture into the outer areas of the shrub, by this time there is often nothing left to eat inside. Before the transformation into the adult form - the box tree moth - pupation takes place in the cocoon, which is also often protected by webs.
Tip: If you are looking for box tree moth caterpillars,should always check the inside of the shrub for droppings and webs. If the caterpillars are already outside, the infestation is usually already very advanced.
Moon caterpillar discovered: what to do?
The following applies to the box tree moth: The earlier you discover an infestation, the easier it is to contain the damage that has occurred. If it is recognized too late, complete defoliation and the death of the box tree are possible. If you only discovered a few larvae in March, you should try collecting them by hand or hosing them off with a hard jet of water. At this point the larvae are too well spun in and cannot be reached by spraying agents. If the small pests are already numerous in spring, you can only wait until they venture out of their protective webs and start eating freely. This is the case from around the second half of April. Now the use of suitable pesticides is also having an effect, because the caterpillars have given up their vital cover to access the entire food supply. We recommend biological agents such as spores of the bacterium Bacillus thuringiensis, which very specifically only parasitizes and kills the caterpillar of the box tree moth. Our Plantura Zünslerfrei XenTari® contains this strain of bacteria and is therefore a biological alternative to conventional sprays.
This year's first and second generation fights earlier: Use traps to determine when moths fly. Two weeks after the flight of the moth, you can get rid of both the eggs and many newly hatched caterpillars with a normal hedge trimming. The resulting clippings belong in a tightly sealed bag with the residual waste to prevent further spread. Once the caterpillars have moved inside the bush, you will have to wait again until the larvae feed freely before spraying them in July or September. With any type of control or control, be sure to also consider the inside of the bush.
Tip: Some birds and wasps have evidently already become accustomed to the toxicity of the borer caterpillars and have accepted them as food alongside the moths. The same applies here: Promoting beneficial insects in the garden is always the right step when it comes to controlling pests.
Summary: What to do when borer caterpillars are spotted?
- In case of slight infestation: collect or spray with water.
- Two weeks after the flight of the moth, the eggs and young larvae can be removed by cutting. Use pheromone traps like the Plantura moth trap to avoid missing the flight of the moth.
- If you can observe freely eating larvae, sprays with Bacillus thuringiesis like our Plantura Zünslerfrei XenTari® show an effect.
- With any control method, make sure that the inside of the bush is also treated.
- Encourage birds and insects in the garden to keep the caterpillars at bay naturally.
We have compiled more detailed information for successfully combating the moth here for you.