Box tree caterpillar

Box tree caterpillars feed within webbing and can completely defoliate box plants. It is a relatively new insect to Britain. Whilst the adult moth was first reported in Britain in 2007, caterpillars were not found in private gardens until 2011, it has since become widely distributed across England (particularly London and surrounding areas) and is present in Wales, Scotland, Ireland and Northern Ireland.

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Box tree caterpillar (Cydalima perspectalis)

Quick facts

Common name Box tree caterpillar
Scientific name Cydalima perspectalis
Plants affected Box (Buxus)
Main symptoms Foliage is eaten and covered in webbing
Most active April-October

What is box tree caterpillar?

Box tree caterpillars are the larvae of a moth that feeds on box (Buxus) plants. It is native to East Asia and it became established in Europe in 2007. Although the first adult moth arrived in Britain during 2007, followed by several moths to light traps in 2008, it was not until 2011 that larvae were reported in private gardens in the home counties. By the end of 2014 the moth had become established in parts of London and surrounding areas; in many cases the caterpillars causes severe defoliation. For growers in the south-east of England it is now a problem that is likely to ​reoccur repeatedly throughout the growing season and in successive years.

Survey

Seen box tree moth? We would like to know.

As part of our research the RHS would like to know where box tree moth has been seen.

Please submit your records via our box tree moth survey (expected time to complete survey = two minutes).

Submissions to our pest and disease surveys are stored permanently in an anonymised form in order to monitor the spread of the pest or disease. We may contact you within 2 months of your submission in order to verify your sighting but your personal data will not be permanently stored in connection with your submission and will be deleted after 1 year. We publish and share only non-identifiable data from survey submissions (such as a six figure grid reference) with third parties and the public for the purposes of scientific research and advancing understanding among gardeners.

Between 2015 and 2016 over 800 records of the moth were received, this jumped to over 3000 in 2017, over 6 000 in 2018 and approaching 12000 in 2019. The box tree moth is now considered to be a "common resident" being widely distributed across England, particularly the south-east. it is also present in Wales, Scotland, Ireland and Northern Ireland.

Thank you to everyone who has submitted records so far – read a blog about the surveys 

Watch an animated map of the results from the box tree caterpillar survey (links to YouTube)

Symptoms

Gardeners are likely to become aware of box tree caterpillar when they find webbing and caterpillars on box plants.

  • The pale yellow flattish eggs are laid sheet-like, overlapping each other on the underside of box leaves
  • Newly hatched caterpillars are greenish-yellow, with black heads. Older caterpillars reach up to 4cm (1¼in) in length and have a greenish/yellow body with thick black and thin white stripes along the length of the body
  • The pupae are concealed in a cocoon of white webbing spun among leaves and twigs
  • The adult moth usually has white wings with a faintly iridescent brown border, although the wings can be completely brown or clear. The moth has a wingspan of around 4cm (1¼in)
  • The caterpillars eat box leaves and produce webbing over their feeding area. Plants may also show patches of dieback which may be especially apparent on trimmed plants. This is not to be confused with dieback caused by the disease known as box blight
  • Caterpillars are also capable of stripping bark which can result in girdling of affected sections

Control

Non-pesticide control

  • Where practical, caterpillars should be removed by hand
  • Pheromone traps which can help monitor adult moth activity are available from several suppliers including Agralan, Dragonfli and Solabiol
  • The mixed nematode biological control sold as Fruit and Vegetable Protection has some effect on the larvae
  • The caterpillars do have a range of natural enemies including parasitoid flies, parasitoid wasps, earwigs, spiders and ants
  • There have been reports of birds such as blue tits feeding on the caterpillars in some locations. It is not yet clear if this predation will result in a reduction of box tree moth numbers
  • Consider choosing alternatives to box plants (see below)

Pesticide control

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

  • Extensive infestations can be treated with an insecticide. Thorough spray coverage is required if control is to be achieved
  • Forceful spraying is needed to penetrate into the interior of box plants through the webbed together leaves
  • Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer). Several applications of these short persistence products may be necessary to give good control
  • More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
  • Follow label instructions when using pesticides 
Plants in flower should not be sprayed due to the danger to pollinating insects. Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.

Downloads

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biological control suppliers (Adobe Acrobat pdf document)

The first occurrance of larvae of the box tree moth Cydalima perspectalis (Lepidoptera: Crambidae) in private gardens in the UK (Adobe Acrobat pdf document)

The box-tree moth Cydalima perspectalis (Walker, 1859) in Britain: an overview of its spread and current status (Adobe Acrobat pdf document)

First records of two natural enemies of box tree moth, Cydalima perspectalis (Lepidoptera: Crambidae), in Britain (Adobe Acrobat pdf document)

Choose alternatives to box

Where it has become impractical to control box tree caterpillar an alternative hedge or topiary plant can be used. Ongoing trials of a variety of compact, evergreen shrubs at RHS Garden, Wisley are showing promise as alternatives. The following all have small leaves and can be clipped into formal hedging styles:

Berberis darwinii 'Compacta'
Berberis thunbergii ‘Atropurpurea Nana' AGM
Elaeagnus × submacrophylla 'Compacta'
Euonymus fortunei (various cultivars)
Ilex crenata
Lonicera nitida 'Maigrün'
L. nitida 'Baggesen's Gold' AGM
Luma apiculata 'Glanleam Gold'
Osmanthus delavayi AGM
Pittosporum 'Arundel Green' AGM
P. 'Collaig Silver'
P. 'Oliver Twist'
P. tenuifolium 'Golf Ball' (PBR)
Podocarpus 'Chocolate Box'
P. 'Young Rusty'
Rhododendron Bloombux ('Microhirs3'PBR)
Taxus baccata 'Repandens' AGM
Ugni molinaeUgni molinae 'Butterball'

Biology

There are at least two generations of the box tree moth a year with the majority of the feeding damage caused between March and October. Box tree moth overwinters as small caterpillars, hidden between box leaves that have been webbed together in late autumn. These caterpillars begin to become active as the weather warms in the spring; larvae have been observed feeding as early as February on particularly warm days. By June caterpillars will have finished feeding, pupated and emerged as adult moths. There is then a second emergence of adults in late July/early August as the next generation of box tree moths emerge looking for mates. Across the summer months over-lapping of generations has been observed, with multiple life stages of the moth present at the same time, however, by late September/October the majority of the population are early instar caterpillars. The adult moths are good flyers and are attracted to light.

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