a white moth and a green caterpillar on a boxwood branch

Box tree moth (Cydalima perspectalis) is a new invasive pest in the United States (not yet in Maryland as of August 2024). 

Updated: August 23, 2024
one page handout about box tree moth

 

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Key points

  • Box tree moth (Cydalima perspectalis) is an invasive insect (moth) native to eastern Asia. This moth was first detected in North America (in Toronto, Canada) in 2018. Though not currently present in Maryland (as of August 2024), box tree moth is a potential new threat to boxwoods. USDA/APHIS has confirmed that box tree moth has been found in Delaware, Massachusetts, Michigan, New York, and Ohio.
  • Box tree moth caterpillars damage boxwood plants by chewing boxwood leaves and bark, leading to leaf browning, defoliation, and girdling. 
  • If you see chewing damage on boxwood leaves, it may be caused by box tree moth. 
  • In the United States, box tree moth caterpillars have only been found feeding on boxwoods (Buxus spp.) so far.
  • Applying preventative pesticides to boxwoods will not effectively control box tree moth. Unnecessary pesticide applications can negatively impact beneficial insects and can even cause secondary pest outbreaks. 
  • Monitor your boxwoods regularly (April through October) and look for the below signs and symptoms of box tree moth. 
  • Be aware of up-to-date federal quarantines for box tree moth. These quarantines help to prevent the further spread of box tree moth through the movement of infested plant material. See this Box Tree Moth Federal Quarantine Boundary Viewer.

Identification

Eggs

small yellow flat eggs on a boxwood leaf
Box tree moth eggs on the underside of a boxwood leaf.

Eggs: Pale yellow, flat-like, overlap, and usually laid in clusters of 5-20 eggs. Each egg is approximately one millimeter in diameter. The eggs are typically laid on the underside of boxwood leaves.

Larvae (caterpillars)

green and black striped caterpillar on boxwood
A box tree moth caterpillar among boxwood leaves and silk webbing. 

Larvae (caterpillars): A black head capsule with a green and yellow body patterned with white, yellow, and black stripes and black spots. The caterpillars like to hide within protective structures made out of silk webbing and leaves, making them difficult to spot at times. Their size varies since they grow larger through each instar (life stage between molts).

Pupae

a green pupal case of box tree moth
A young box tree moth pupa.

Pupae: Young pupae are green with brown stripes. Mature pupae become more translucent and you can begin to see the adult moth wing patterns. Pupae are around 20mm (0.8 inches) long and are typically found within damaged boxwood leaves and webbing/silk.

in a pupal case of box tree moth you can see the wings forming
A mature box tree moth pupa.

Adult moths

a white and black moth - box tree moth
One of the two adult box tree moth color variants: white body and white wings with brown-bronze wing margins and a small white marking on both top wings.

Adult moths: There are two different color variants. One variant has a white body and white wings with bronze-brown wing margins and a small white marking on both top wings. The second color variant has a brown body with brown wings with a small white marking on either top wing. Box tree moth wingspans range from 40-45 mm (~1.5 inches). Adult moths are nocturnal (active at night).

brown boxwood moth
One of the two adult box tree moth color variants: brown body and brown wings with a small white marking on both top wings.

Damage

chewed boxwood leaves and the box tree moth caterpillar
Box tree moth feeding damage, silk webbing, and caterpillar.

Chewing damage: Injury begins with young caterpillars that chew on the undersides of leaves, removing one layer of leaf tissue. Older caterpillars can defoliate leaves either by consuming the entire leaf or by just leaving behind the leaf edges and/or leaf midvein (creating a "curlicue" leaf appearance). Extensive feeding can result in "see-through" brown boxwoods and potentially plant death. Box tree moth caterpillars have also been observed chewing boxwood bark, leading to girdling (a circular groove around a woody stem that cuts off the movement of nutrients) and potentially plant death.

a boxwood plant with chewed up leaves and caterpillar webbing
Box tree moth damage. Photo: Joe Boggs, OSU Extension

Silk and Frass

pellets of frass from box tree moth
Box tree moth caterpillar with silk webbing and frass pellets (excrement).

Silk and frass: Caterpillars produce wispy silk webbing, sometimes used to connect leaves and branches together to create protective structures. Small light green-brown frass pellets (excrement) can be found within silk or on the ground underneath infested plants.

Overwintering structures (hibernacula)

box tree moths overwinter as caterpillars
A box tree moth hibernaculum (overwintering structure). Photo: Joe Boggs, OSU Extension

Overwintering structures (hibernacula): Hibernacula (sing. hibernaculum) are structures created by caterpillars for protection during the cold winter months. The structure is usually created out of a silken pouch attached to one or more leaves.

a striped caterpillar emerging from a damaged boxwood leaf - box tree moth
A box tree moth hibernaculum (overwintering structure) pulled apart to reveal the caterpillar. Photo: Joe Boggs, OSU Extension

Annual timeline

a timeline for box tree moth through the year - caterpillars active starting in April

Caterpillars emerge from their leaf and silk overwintering structures around April, developing over a span of ~28 days, through a pupal stage, to reach their adult moth form. Adult moths will lay eggs and a course of multiple overlapping generations will take place between May and October. Around October, caterpillars will create their overwintering structures and remain there until the following spring. This is a generalized annual timeline and is subject to change based on further data and records. Figure created by Madeline Potter, UME.

Lifecycle

  • Box tree moth can have several overlapping generations; the number of generations and length of the different developmental stages varies by location and weather conditions. So far box tree moth has been observed to have between two to five overlapping generations per year. 
  • Around April caterpillars emerge from their overwinter structures, called hibernaculum (created out of silk and leaves attached to a boxwood). The caterpillar will begin feeding and grow through as many as seven instars (life stages between molts), over a span of approximately 14 days, before reaching their pupal stage. 
  • Mature caterpillars will form a pupa, attached to a boxwood plant, to finish their development. The pupal stage lasts approximately 14 days.
  • Adult moths emerge from their pupa to seek mates and lay eggs. They have a lifespan of about 14 days.
  • Eggs develop and hatch in approximately three days. 
  • Between May and October box tree moth will produce several overlapping generations.
  • Around October caterpillars will create their overwintering structures where they will remain, in diapause (dormancy/suspended development), through the cold winter months until the following spring. 

Management

  • Confirm the identification of box tree moth by submitting photos through Ask Extension before applying controls. Unnecessary treatments can harm beneficial insects and cause secondary pest outbreaks. Do not apply preventative insecticide applications.
  • With small infestations, hand-pick or prune caterpillars off plants and place them in a bucket of soapy water.
  • For large infestations, use a horticultural oil or insecticidal soap spray on small caterpillars, following all label instructions. Please note: adequate coverage is needed for effective control, aiming for the underside of leaves (where the young caterpillars feed). A professional pest control company can be contacted for further guidance.
  • Heavily infested plants may need to be removed and destroyed to prevent further spread.
  • Further management options are currently being researched.

Reducing the spread of box tree moth

  • Box tree moth is spread through the movement of infested boxwood nursery stock and adult moth flight. One study in Europe suggested adult moths can sustain flights of over 20 miles. Be sure to check for signs of box tree moth on any boxwoods you purchase and on any existing boxwoods in your landscape.  If you believe you have seen box tree moth or its damage, send reports and photos to Ask Extension.
  • Within current box tree moth quarantined areas (see Box Tree Moth Federal Quarantine Boundary Viewer), boxwood (Buxus spp.) plants may only be moved interstate from an establishment operating under a compliance agreement (PDF) and a certificate issued by a State Agricultural Authority (see May 2024 Federal Order (PDF)). There are currently no box tree moth quarantine areas within Maryland.

Video: Check Your Boxwoods for the Box Tree Moth! Source: USDA Animal and Plant Health Inspection Service

Additional resources

Author: Madeline Potter, Faculty Specialist, Entomology & Integrated Pest Management (IPM), University of Maryland Extension, August 2024. Unless otherwise noted, all images are from Adobe Stock.

Still have a question? Contact us at Ask Extension.