​​Box Tree Moth

What is it and why does it matter?

The box tree moth or BTM, Cydalima perspectalis (Walker), is an invasive moth native to eastern Asia. It has invaded Europe and North America.  It has not been found in Pennsylvania, but is currently known to be in Ontario, Canada, Michigan, Ohio, New York, and Massachusetts. The primary means of introduction in all areas outside its native range is through importation and sale of infested boxwood nursery stock. 

The BTM feeds on the foliage of boxwood plantings (Buxus spp.) as a caterpillar and heavy infestations can fully defoliate plants. Caterpillars also feed on bark, girdling the plants and causing death. Because there are no natural predators, box tree moth populations can reach high densities, limited only by available food sources.

Boxwoods are an important part of landscaping in Pennsylvania and is a traditional plant used for topiary and hedges. It is planted in many historic and public gardens. It is the highest-selling evergreen shrub in the U.S. Approximately 150 cultivars of boxwood are available to homeowners, and all are susceptible to this invasive pest. 
  

Lifecycle and what to look for and look-alikes

The eggs are laid as clusters of flat, scale like deposits, typically on the underside of leaves. The clusters can be made up of 5-20+ yellow orange eggs, occasionally with a black spot as they near maturity. The eggs hatch in about 3 days and the caterpillars begin feeding on the leaves. 

Newly hatched caterpillars are green to yellow with black heads. As the caterpillars mature horizontal stripes of white, yellow, and black begin to appear along the length of the body. Black spots on the top of the caterpillar are located between the darker stripes. 

Early caterpillars are approximately .25" long and older caterpillars reach up 1.5". Damage from the feeding will be from the leaf margin early on. As the infestation progresses feeding will lead to skeletonization, removing almost all leaf tissue and leaving the midrib behind. Silk webbing made by the caterpillars will also start to appear as loosely placed strands between branches and leaves. Severely infested plants may take on a scorched brown look. 

Adult moths have two distinct forms, a light and a dark morph. The light morph has mostly white wings with a white body. The dark morph has dark wings with small patches of white and a dark body. The wingspan of both morphs ranges from 1.5 to 1.8 inches and have comma shaped marks on the forewing. 

Look-alike moths you might encounter include the melonworm moth (Diaphania hyalinata) and the pickleworm moth (Diaphania nitidalis). These moths do not regularly occur in Pennsylvania and lack the white comma mark on the wings, but my occasionally drift up from the southern United States.

Recognizing Boxwood and Look-alikes

Boxwood have been grown in the United States since colonial times, brought over by colonists. The most frequently seen are common boxwood (Buxus sempervirens) and the English variety (Buxus sempervirens 'Suffruticosa'). Boxwoods are often grown in trimmed hedges of various sizes and shapes but can reach 25 ft in height if unpruned. The new foliage is blue green that darkens into a glossy dark green on top and a yellow green on the underside. The narrow ½ to 1 ½" leaves grow opposite on a square stem and produce dense foliage that is evergreen. Boxwoods also carry a distinctive smell that some consider unpleasant. 

• Bayberry (Myrica pensylvanica) - Leaves has a spicy scent when crushed.  Fruits are a waxy gray color with a bumpy irregular surface. 
• Inkberry Holly (Ilex glabra) – Leaves are longer than a boxwood, tend to overlap and are alternate on the branches.  If the plant produces fruit, the berries are a showy black color.
• Japanese Holly (Ilex crenata) - Leaves are alternate on the branches.
  
  

How to stop Box Tree Moth and Report Sightings

Early detection is key to preventing to significant damage, loss, and spread of BTM if it appears in Pennsylvania. If you become aware of something that looks like BTM, please submit a report to badbug@pa.gov or to 1-888-253-7189. Please indicate which life stage was found, if damage was present, and include any photos you have. You can contact your local PSU Extension office for treatment information.