Boxwoods usually have to contend with insect issues like boxwood leafminer or boxwood psyllid. In recent years, we have had concerns arise over boxwood blight, also impacting Kentucky boxwood plants. Now, it seems like a new invasive is on the horizon that could attack these commonly planted shrubs— box tree moth.
What is the box tree moth?
Box tree moth is an invasive species originally from Asia (specifically China, Japan, Korea, and Eastern Russia) and it has been highly problematic for over 25 European nations since first appearing in Germany in the mid-2000s.
Previously, the only North American infestation was located in Ontario, Canada. However, that changed at the end of May 2021 when reports were released that this pest had been discovered in Michigan, Connecticut, and South Carolina. The USDA is taking immediate action to try and contain the issue and stop this from happening again, but we need to be vigilant to make sure we help contribute to monitoring programs.
In its final instar, the box tree moth caterpillar is about a half inch long. They are primarily yellow green in color, with black and white stripes that run vertically down the body on each side (Figure 1). On each abdominal segment there is a pair of black dots.
The adult moth is broadly fan shaped. For the majority of adults, the exterior margins of their wings are brown and there is an inner white triangle that spans the wings and body. Some adults may be completely brown. The box tree moth superficially resembles the melonworm moth in coloration and the patterns on their wings. The box tree moth has white comma-like markings near the wing margins that the melonworm lacks.
Thus far, box tree moth has only been observed to feed on boxwood plants in the genus Buxus. Currently, there are no known resistant varieties of boxwood.
What does it do?
Box tree moth larvae feed on the leaves and the bark of boxwood plants. The younger larvae feed on the undersides of leaves, creating a papery or peeling appearance. As they mature, larvae will eat entire leaves, leaving behind only the midrib. As the plant is defoliated, the larvae will move to feed on the bark, inducing girdling and possibly killing the plant. Older caterpillars also produce noticeable webbed enclosures. These are messy and may contain the caterpillar, its frass, and old cast off “skins.”
How is it different from other boxwood insect pests?
Boxwoods are also hosts to boxwood leafminers and boxwood psyllids that may leave behind damage. Box tree moth is the only caterpillar pest of boxwoods, and their damage is different in comparison to our other pests. Boxwood leafminers cause the leaves to appear blistered as they feed from the inside. There is also an orange or bronzed color caused by their damage, which is focused in the newest growth. Similarly, boxwood psyllid prefers to attack the newest foliage, but they cause the leaves to cup inward on themselves.
What to do if you believe you have found this pest
If you fear you have spotted damage from this pest or have captured a specimen, please contact us at the Department of Entomology or reach out to the Office of the State Entomologist to begin the process of confirmation. We are hopeful we can keep this invader from the state and we appreciate receiving tips from the field.
By Jonathan L. Larson, Entomology Extension Specialist
Kentucky Pest News 