Invasive Box Tree Moth Spotted in Philadelphia

First it was the menancing  spotted lanternfly — and now there’s a new invasive insect in town.

Earlier this week, the Pennsylvania Department of Agriculture announced that the “highly destructive” box tree moth, which originally hails from Asia, has officially entered the state.

The moth was spotted in two Erie County cemeteries, which are now quarantined. It has also appeared in Delaware, Massachusetts, Michigan, New York, Ohio and Ontario, Canada.

The good news is, unlike the spotted lanternfly, which harms a wide range of plants, the box tree moth has only one victim: boxwoods, a non-native shrub commonly used for hedging and topiary.

“It’s one of the most popular ornamentals,” said entomologist Michael Skvarla, an assistant research professor at Penn State who runs their Insect Identification Laboratory. “So, yay — it’s not going to hurt native ecosystems, but it is going to have a sizable impact because boxwood is so extremely popular all over the place.”

As Liz Tung reported, most adult box tree moths are primarily white, with a border of brown along the edges of their wings. Around 5% are completely brown. Skvarla says they bear a slight resemblance to melonworm moths, which are native to North America, but are otherwise distinctive for our area.

By the time you’re noticing moths, however, the damage may already be done.

“The caterpillar stage is the most damaging stage,” Skvarla said. “It’s the almost mature caterpillars that are doing the majority of feeding. It can kill boxwoods quickly. There are some reports that boxwoods will die within a year of heavy feeding. Part of the problem is the caterpillars, especially in heavy infestations, will strip all of the leaves off of the boxwood. Once they strip the leaves, if they’re still hungry, they’ll start chewing on the bark.”

Boxwoods may be able to recover from damage to their leaves, but once the caterpillars start stripping the bark, entire branches can die off — which can mean death for the plants. So soon as you see them, pluck them away and cut off damaged areas of plants.

The first step for anyone who suspects they might have an infestation is to monitor their boxwoods, says Patricia Prade, an entomologist with Penn State Extension who specializes in controlling pests and invasive species.

“You need to know if you have this insect,” Prade said. “So you need to constantly check if you see any larvae.”

One way to confirm whether or not you have an infestation is to purchase pheromone traps geared specifically toward box tree moths.

Prade says there are a few options for curbing box tree moths. Her first suggestion is to simply pluck them off, or trim away the infested areas.

“If you’re a homeowner, for example, and you see some caterpillars, you can handpick them and kill them easily,” she said. “It can be challenging if you have a lot of plants infested, but if you have just a couple, you can cut a branch or something like that. That’s very targeted, right? It’s a very good way to control them fast and not to just spray chemicals on the environment.”

Because box tree moths are so new, Prade says, studies are still being done to find out what chemicals are most effective against them while being the least damaging to other life. In the meantime, she says, homeowners can seek out pesticides targeted toward caterpillars, which are likely to kill box tree moths.