Box Tree Moth

Damage caused by box tree moth caterpillar feeding viewed on plants in Barnstable County, MA in 2023. Photo courtesy of Russ Norton, Cape Cod Cooperative Extension.
Box tree moth caterpillar, webbing, and frass pellets. Seen in Barnstable County, MA in 2023. Photo courtesy of Russ Norton, Cape Cod Cooperative Extension.
Box tree moth caterpillar feeding, webbing, and frass pellets. Seen in Barnstable County, MA in 2023. Photo courtesy of Russ Norton, Cape Cod Cooperative Extension.

Order: Lepidoptera
Family: Crambidae
Cydalima perspectalis

Overview

The box tree moth (Cydalima perspectalis) is a non-native insect that originated in the temperate and subtropical regions of Asia. It was found to be invasive in Europe in 2007 and has since spread to western Asia, northern Africa, and Canada (2018). In the United States, it has been detected previously in New York (2021), Michigan (2022), and Ohio (2023). It was first detected in Massachusetts in communities on Cape Cod (Barnstable County) in August of 2023. Thus far, the established populations of box tree moth in MA are in landscape plantings that are two or more years of age. It is currently unclear how widespread box tree moth is on Cape Cod, or how the infestation was introduced. The MA Department of Agricultural Resources (MDAR) and the United States Department of Agriculture, Animal and Plant Health Inspection Service (USDA-APHIS) are currently working to delimit the infestation found on the Cape. It is important that if you suspect you have found this insect in Massachusetts, you report it to MDAR, here: https://massnrc.org/pests/report.aspx . (If you are in Barnstable County, MA, there is no need to report box tree moth to MDAR. All other counties in Massachusetts should report suspicious insects or damage to boxwood.) More information about box tree moth in Massachusetts can be found from MDAR, here: https://massnrc.org/pests/pestFAQsheets/boxtreemoth.html .

Host Plants

As the common name would suggest, the primary hosts of the box tree moth are boxwood (Buxus spp.). However, this insect has previously been reported to feed on the following in its native range: burning bush (Euonymus alatus), Japanese spindletree (E. japonicus), purple holly (Ilex chinensis), and orange jessamine (Murraya paniculata) if heavily infested boxwoods are present in the same area. Recent assessment of the likely host range of box tree moth in the United States by the USDA APHIS has concluded that Ilex spp. are not hosts of box tree moth and that the initial reports of Euonymus as hosts for this insect are also incorrect. As such, APHIS has determined that Ilex and Euonymus are unlikely pathways for this insect to spread. However, due to the newness of this information, printed and online resources may still list them as potential host plants.

Identification/Life Cycle

Adult box tree moths are white with a brown head and abdomen. Wings are white and slightly iridescent, with an irregular thick brown border (1.6 to 1.8 in. wide). Part of the adult population has completely brown wings with a small white streak on each forewing. Both color forms may be found in the male as well as the female. 

Eggs of the box tree moth are pale yellow and average 0.04 in. in size. They are laid in flat clusters (gelatinous mass) of about 5 - 20 on the underside of boxwood leaves. Eggs take approximately 3 days to hatch. 

The box tree moth overwinters in the caterpillar life stage in a cocoon protected by webbing in the leaves. They can withstand temperatures as low as -22F. Once temperatures warm in the spring, the caterpillars begin feeding again. Young caterpillars feed on host plant leaf undersides. As they mature, a black spot appears on the head of the larval caterpillar. Newly hatched caterpillars have black heads and are green to yellow in color. As they age, the coloration of the caterpillar changes even further and dark brown stripes develop on the body. The most mature caterpillars are approximately 1.6 in. long and have thin white and thick black stripes and black dots outlined in white along the length of the body. 

Depending upon local temperatures, caterpillars may feed from approximately March until they pupate in April or May in warm locations. In cooler areas, feeding may not occur until late May to early June. As they develop, they spin silken webs to hold leaves together and create protected areas to feed. They tend to feed on leaves in the lower portion of host plants but can also be found in the upper portion of the plant. Subsequent generations of caterpillars can remain active until September or October. 

Pupae develop inside a silk cocoon and are 0.6 to 0.8 in. long. They are initially green, with black stripes on the back, and turn brown as they mature. Pupae can be present continuously from the summer into the fall. Adults can emerge from the overwintering generation from April-July. Subsequent generations of adults may be found from June-October. Adults live for two weeks on average. The exact timing of the life cycle in Massachusetts is not fully understood at this time. Several overlapping generations are expected to occur per year, with an estimated 1-5 generations possible from May to September.

Damage

The most damaged host plants of the box tree moth are boxwoods (Buxus spp.). In the United States, the USDA estimates that boxwood sales are worth approximately $126 million (2015). Heavy defoliation of ornamental boxwoods can occur if this insect is not managed. Defoliation of existing or new growth can eventually lead to plant death. Once the caterpillars have eaten all of the host plant leaves, some have been observed to strip bark from branches or main stems, which may also lead to host plant mortality. This damage may be difficult to see in the beginning of an infestation. Young, tiny larvae are good at hiding among host plant leaves and branches. Eventually, defoliation, webbing, and green-black frass pellets may be noticed as a result of box tree moth infestation. Defoliated leaves may appear “peeled” or with only a midrib remaining. Severely infested plants look brown or scorched. 

Management Strategies:

Box tree moth is a Federally regulated species and its distribution in MA is currently very limited. The most important and first management step at this time is to report box tree moth, if found in Massachusetts, to the MA Department of Agricultural Resources, immediately: https://massnrc.org/pests/report.aspx . (If you are in Barnstable County, MA, there is no need to report box tree moth to MDAR. All other counties in Massachusetts should report suspicious insects or damage to boxwood.) Take photos and note your exact location. Do not move infested boxwood plants or other susceptible hosts from the area. Be aware that box tree moths are readily transported via infested boxwood plants, and in Europe it is estimated that they travel up to an average of 96 miles per year this way. These moths are also good fliers, and natural dispersal (in Europe) has been estimated to be 3-6 miles per year.

Visual monitoring for box tree moth in boxwood plantings can be conducted by searching for defoliation including leaves eaten to the vein, browned/scorched appearance of leaves, webbing, and dark green frass pellets. Pheromone lures and traps for monitoring box tree moth exist, and may be commercially available. Traps and lures are (at this time) assumed to be able to attract box tree moths from 25 meters away.

Cultural/Mechanical Management:

Take care to reduce the risk of spreading box tree moth to new locations. If you are removing clippings or entire shrubs from a previously confirmed (with MDAR) infested site, bag the infested plant material and safeguard it on site. Potential methods of dealing with infested plants include burial, chipping, or burning. Consult local ordinances if burning. On small plantings or lightly infested plants, caterpillars can be hand picked and dropped into a bucket of soapy water to kill them. 

If replanting is necessary, choose an alternative replacement shrub. Consider not replanting with boxwoods in an infested area. Some suggested alternatives to boxwood, depending upon site conditions and the needs at the site, include but are not limited to: bayberry (Myrica pensylvanica), dwarf hinoki cypress (Chamaecyparis obtusa ‘Nana’), inkberry holly (Ilex glabra), Japanese holly (Ilex crenata), and plum yew (Cephalotaxus harringtonia).

Biological Control/Natural Enemies:

At this time, the effectiveness of natural enemies at reducing box tree moth populations to acceptable levels in the United States is unknown. Classical biological control, or the release of parasitoids or predators from the native range of the insect, is not currently available.

Natural enemies of the box tree moth are reported in the literature. Chelonus tabonus, Tyndarichus spp. and Trichogramma spp. are reported to parasitize box tree moth eggs. Casinaria spp., Compsilura concinnata, Dolichogenidea stantoni, Exorista spp., Protapanteles mygdonia and Pseudoperichaeta nigrolineata are reported as larval parasitoids of box tree moth. In laboratory studies, entomopathogenic nematodes Steinernema carpocapsae and Heterorhabditis bacteriophora caused high mortality of box tree moth larvae. Brachymeria lasus and Apechthis compunctator are reported pupal parasitoids of box tree moths. 

Chemical Management:

With large plantings or thoroughly infested plants, chemical management options to treat box tree moth may be practical. Integrated Pest Management (IPM) strategies to reduce dependency on chemical insecticides and protect the health of the applicator and the environment are encouraged. When possible, choose the lowest risk active ingredient to manage any insect pest.

If using contact insecticides, thorough coverage of the interior of the boxwood shrubs as well as penetration of the webbing created by the caterpillars is necessary to increase the effectiveness of the application. The lower area of the plant may be most fed upon, however caterpillars may be living in the upper area of the plant.

Homeowners in areas of Massachusetts where box tree moth has become established may need to hire a professional, licensed pesticide applicator to help with chemical management. Box tree moth is present in a small area of Massachusetts. Chemical management in areas of the state where this insect has not been confirmed to exist is unnecessary at this time. 

Some active ingredients that may be used to manage caterpillars, such as box tree moth, include but are not limited to:

*Abamectin (NL) (systemic insecticide, injection)

Acephate (NL) (systemic insecticide, injection)

Acetamiprid (L) (systemic insecticide, injection)

Azadirachtin (NL) (systemic insecticide, injection, soil drench)

Bacillus thuringiensis Aizawai (L) (contact insecticide)

Bacillus thuringiensis Kurstaki (NL) (contact insecticide)

Bifenthrin (NL) (contact insecticide)

Carbaryl (L) (contact insecticide)

*Chlorantraniliprole (NL) (systemic insecticide, soil drench)

Cyantraniliprole (NL) (systemic insecticide, soil drench, soil injection)

Cyfluthrin (NL) (contact insecticide)

Deltamethrin (L) (contact insecticide)

*Emamectin benzoate (L) (systemic insecticide, injection)

Gamma-cyhalothrin (L) (contact insecticide)

Insecticidal soap (NL) (contact insecticide)

Lambda-cyhalothrin (L) (contact insecticide)

*Methoxyfenozide (NL) (contact insecticide)

Neem oil (NL) (systemic insecticide, soil drench)

Pyrethrins (L) (contact insecticide)

Pyrethrins + sulfur (NL) (contact insecticide)

*Spinosad (NL) (contact insecticide)

*Tau-fluvalinate (NL) (contact insecticide)

Zeta-cypermethrin (L) (contact insecticide)

*Active ingredients that are noted to have >95%-100% efficacy in Table 5-1, Page 29, from the USDA-APHIS New Pest Response Guidelines for Box Tree Moth.

Read and follow all label instructions for safety and proper use. If this information contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations.

References

Authors

Tawny Simisky, Entomologist, UMass Extension
Russ Norton, Horticulturist, Cape Cod Cooperative Extension

Author: 
Tawny Simisky and Russ Norton
Last Updated: 
August 2023