BETHLEHEM, Pa. — It’s not at all surprising that box tree moths, an invasive insect, have been recorded in Pennsylvania, Marten Edwards said — they’ve already infested boxwoods in neighboring states.
“Insects don’t have any respect for our maps, and they can easily be spread by moving infested plants from one place to another,” said Edwards, a Muhlenberg College biology professor. “Even though there are about 150 different varieties of boxwoods, with a huge variety of growth forms, they are all the same species and are vulnerable to attack by this insect.”
Earlier this month, state agriculture officials announced the box tree moth, a highly destructive, invasive insect, was discovered for the first time in the commonwealth, in two cemeteries in Erie County. While a quarantine has been issued in an attempt to stop their spread, it’s up to residents and businesses to abide by it in order for it to be successful.
In the meantime, there are steps Lehigh Valley residents can take to prepare.
This insect does not harm humans or threaten our food supply. It threatens livelihoods in our nursery and landscape industry, as well as the parks and gardens that enrich our communities and feed tourism dollars into our economy.Pa. Agriculture Secretary Russell Redding
“This insect does not harm humans or threaten our food supply,” said Agriculture Secretary Russell Redding, in a news release. “It threatens livelihoods in our nursery and landscape industry, as well as the parks and gardens that enrich our communities and feed tourism dollars into our economy.
“Protecting communities and businesses from economic loss is a top priority of the Shapiro Administration.”
The insect feeds on and destroys boxwoods, which are often used as topiaries and hedges and are the largest-selling evergreen shrub in the U.S., officials said. The moth has been previously found in Delaware, Massachusetts, Michigan, New York and Ohio, as well as Ontario, Canada.
“Pennsylvania’s nursery and landscaping industry generates $4.1 billion for the state economy annually and is responsible for more than 63,000 jobs,” according to the release. “Pennsylvania leads the nation in the number of floriculture businesses — those that produce garden and bedding plants, potted plants and cut flowers.”
Here's LehighValleyNews.com’s interview with Edwards. Some answers were edited for style and clarity.
Q: What is a box tree moth?
A: It is the adult stage of a caterpillar that feeds on boxwood. The lime-green caterpillars have black stripes, white spots, hairs and a shiny black head.
Q: Where did they come from?
A: These insects are native to East Asia, but they were first observed in Europe in the 2000s and spread to Canada and eventually New York State in 2021.
Q: What kind of environment do they thrive in?
A: They seem to thrive wherever boxwood plants are found.
Q: What does their life cycle look like?
A: Moths lay their eggs on the underside of boxwood leaves and take about three days to hatch. Depending on the weather conditions, the caterpillars generally develop into adult moths in about two weeks. They can give rise to several generations between May and October.
They overwinter as caterpillars and can survive at temps as low as -22 degrees Fahrenheit, which is much colder than we typically experience in the winters here in the Lehigh Valley
Q: At what stage are they most destructive, and on what do they feed?
A: The caterpillars feed on boxwood leaves. They may eat all the leaves off the plant. In the case of heavy infestations, they will even eat the bark off the boxwoods. By “girdling" the shrub, they can kill it.
Q: How do they spread?
A: The caterpillar stage can be moved in boxwood plants when they are transplanted or bought at nurseries. This is the most important (and preventable) form of transport. This is why there is a quarantine on moving any boxwood trees from counties that have known infestations.
Q: Although there's been a quarantine put in place, what are the chances it'll be successful at stopping the spread?
A: Quarantines only work as well as people understand why they are important and respect them, even if it comes at some cost or inconvenience. I think we should expect this insect to reach the Lehigh Valley, since there are lots of boxwoods and our weather conditions are certainly permissive.
This insect has been able to spread through all of Europe since 2006, so I can’t think of any good reason it should not be established here. Delaying the spread as much as possible is beneficial to give gardeners a chance to plan and respond appropriately.
Q: Are there insecticides available for treatment, or a method to control the population?
A: Yes, starting with respecting the quarantine! Once they are here, there are some methods recommended by the Pennsylvania Department of Agriculture. According to their excellent website, early detection is key to preventing significant damage, loss. If you become aware of something that looks like a box tree moth, 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.
Q: Is there anything else residents should know?
A: Even though boxwoods are one of the most popular garden plants and have been part of our landscape for centuries, there are no native boxwood trees here in the United States. So far, the box tree moth only seems to feed on boxwoods. Let’s hope they don’t decide to branch out with their food choices. Insects that have evolved over millennia to feed on native plants also have a host of natural enemies. In their native range in Asia, these caterpillars are kept in check by predators, but we don’t have the same predators here, which is why their populations can get out of control.
Native plants are essential for providing the base of stable food chains and are often the best choice for landscaping. There are some native alternatives that will provide an attractive and worry-free work-around. For example, according to the Penn State Extension service, bayberry is a native shrub that tolerates many types of soils, endures road salt runoff, forms privacy screens, bears fruit enjoyed by songbirds and is not damaged by deer. Our native hollies provide a spectacular winter display with lots of berries for wildlife to munch on.
