Meet Delaware’s newest invasive species: the box tree moth.
The box tree moth is native to East Asia and primarily feeds on boxwood plants. Its first appearance in the United States was in New York in 2021. Since then, the moth has spread to Massachusetts, Michigan, Ohio and, as of July, Delaware.
According to a July 15 Delaware Department of Agriculture press release, the box tree moth was found at a private residence in Kent County.
In a fact sheet released by the university’s insect pest management (IPM), box tree moth caterpillars are described as “green and hairy, with black stripes and white dots,” while adult moths are described as “white with a thick brown border on the wings, and are active at night.”
The intensity of the species’ feeding habits can ultimately threaten the wellness of the boxwood plants they consume. Box tree moths can defoliate boxwood plants entirely and feed on the plant’s bark, causing serious damage.
The boxwood plant family is comprised of roughly 70 different shrub-like plant species. Some of their distinctive features are dense foliation and evergreen leaves.
“If we don’t treat them, they’ll kill our boxwoods,” Brian Kunkel, ornamental IPM extension specialist at the university, said.
“Plants need leaves to photosynthesize, that’s how they get their food,” Kunkel said. “As the caterpillars eat, they’re reducing the amount of food produced by the plant. The caterpillar strips bark off the stems once the leaves are gone. Leaf and bark removal leads to plant death.”
Since it arrived in the U.S., the box tree moth has had a lot of success growing its population. Kunkel explained how this could be attributed to the insect’s lack of natural predators, a suitable climate and an abundance of boxwood plants for food.
“It’s currently in a relatively open habitat for it to expand and feed,” Kunkel said.
Additionally, the box tree moth can produce anywhere from two to five generations in a year, allowing the species’ population to grow rapidly.
Andrew Adams, horticulture manager at the university’s Botanic Gardens, is hopeful of the university’s ability to handle the pests if they were to make it on campus.
“Luckily, at UD, there’s not a ton of boxwoods,” Adams said. “We’ve slowly been shying away and using different plants.
“Up campus, they’ve been pulling up boxwoods because they’ve been dying from blight and other issues they have,” he said. “So inadvertently, we’ve almost prepared ourselves and will probably take a minimal hit from this.”
While the university may experience a limited impact from the box tree moth, Adams points out that residential areas are far more at risk.
“The economic problem is that so many boxwoods are used in landscapes,” Adams said. “It’s a really big issue in residential areas because a new contractor planting tends to always have boxwoods in it even though there are a lot of other alternatives.”
The box tree moth has yet to be spotted anywhere other than the property it was initially discovered on in Kent County. However, Adams believes it is only a matter of time until the insect makes its way up to the university’s campus.
“We might not see any this year,” Adams said. “But I think early next spring we’ll probably see them start to pop up around here. But that gives us time to prepare, look at alternatives and things like that.”
The university IPM fact sheet wrote “damaged boxwood leaves may appear ‘peeled’ or only have the mid-rib left behind,” while heavily infested boxwoods “may appear brown, ‘see-through’ or ‘torched.’”
If you spot a box tree moth, the Delaware Department of Agriculture asks that you contact Delaware Cooperative Extension Master Gardeners at the Garden Helpline through the following information:
- New Castle County: 302-831-8862
- Kent County: 302-730-4000
- Sussex County: 302-831-3389