The non-native Box Tree Moth (BTM) (Cydalima perspectalis, family Crambidae) feeds exclusively on boxwood (Buxus spp.). We think of boxwoods as shrubs. However, the “tree” in the common name refers to the tree-like growth of native boxwoods in Europe as well as Asia, where BTM is native. Despite there being an “American Boxwood,” boxwoods are not native to North America.
Additional quarantines to prevent the spread of the moth continue as new infestations are discovered in the U.S. Since its discovery in the Lake Ontario region of New York in 2021, BTM has been found in Delaware, Kentucky, Maryland, Massachusetts, Michigan, Ohio, Pennsylvania, Virginia, and West Virginia.
The USDA Animal and Plant Health Inspection Service (APHIS) BTM website includes a quarantine map that was updated on August 27. The entire states of Massachusetts and West Virginia are quarantined; however, it does not mean BTM infestations are border-to-border in those states. It was a regulatory decision.
What’s Happening in Ohio?
The Ohio Department of Agriculture (ODA), along with an associated network of OSU Extension Educators, has been maintaining BTM detection traps throughout this season. The traps are baited with a synthetic version of the pheromone produced by female moths to attract males. The traps only attract males, so they don't contribute to the spread of BTM.
Based on trapping and visual scouting, BTM Quarantines in our state have been expanded since January. This does not mean we’re out of the woods with BTM. It just means no infestations have been detected outside of the current quarantine zones. The bottom line is that we must remain vigilant.
To learn what to look for in detecting BTM, see our OSU Extension Fact Sheet titled Box Tree Moth: Detection, Part 2 of 3 in the Box Tree Moth (BTM) Series. The hotlink will take you to a printable PDF version.
Interesting Events in SW Ohio and Rampant Speculation
BTM overwinters as early instar caterpillars in a physiological resting state called diapause. They are hidden away in a protective structure called a hibernaculum (plural: hibernacula). This produces a “split generation” as shown in the graphic below.
The caterpillars emerge from diapause in early spring to feed voraciously. The resulting rapidly developing defoliation commonly reveals new infestations.
As the season progresses, BTM produces two, or possibly three, overlapping generations in the southern part of Ohio. Overall populations build with each generation, and this population trajectory has been consistently observed elsewhere in the U.S. The life cycle is illustrated in the graphic below.
However, BTM populations in Greater Cincinnati have followed two tracks this season depending on how long BTM has existed in a location. BTM was first discovered in the Loveland area east of Cincinnati in 2023. Successive seasons of multiple generations have produced some substantial injury to boxwoods.
However, there remains a significant number of boxwoods, but I had difficulty finding active infestations in and around Loveland in June, July, and early August. In some cases, BTM damage was evident, but I could find no caterpillars.
There was no indication that BTM populations had been affected by environmental events, heavy predation, or perhaps entomopathogenic infections. Based on rampant speculation, I believe the suppressed populations represent widespread insecticide applications in a location where homeowners and landscape managers are acutely aware of BTM.
Conversely, I recently visited a private landscape in Anderson Township that had a high population of BTM caterpillars producing heavy damage. The township is located southeast of Cincinnati, and the site visit was approximately 16 miles south of Loveland.
The homeowner described a population trajectory consistent with the spread of BTM into new territory. They did not detect BTM early in the season; no damage was observed. However, over the past few weeks, both the damage and BTM population seemed to explode.
Two things were possible. Either moths flew in during the season to initiate the infestation, or the infestation was brewing undetected until caterpillar numbers climbed through subsequent new generations to reveal the presence of an infestation.
The latter possibility illustrates a key caterpillar feeding behavior that presents a challenge to detecting a developing BTM infestation. BTM caterpillars tend to feed “inside out” on their boxwood hosts. They commonly focus on the interior foliage with the outer foliage hiding their presence.
As the population expands and the caterpillars exhaust their food supply, they are revealed by being forced to feed on the outer foliage. The bottom line is that early detection requires parting the foliage to peer inside boxwoods.
The infestation in Anderson Township had both early and late instar caterpillars as well as pupae. This suggests that the infestation had progressed through multiple generations that are now overlapping.
Another observation that should be considered in detecting BTM is the possible occurrence of a large number of damaged leaves that remained attached. Early-instar BTM caterpillars do not consume entire leaves. They consume the leaf mesophyll, removing the upper or lower leaf epidermis. However, the damaged leaves remain attached.
Older-instar BTM caterpillars consume leaves, and disappearing leaves have long been used as a key symptom of BTM damage. Whole leaves remain attached until they drop if boxwoods are suffering from Volutella Canker and Blight, Boxwood Blight, and winter injury.
However, it’s important to closely examine leaves that remain attached to look for evidence of early instar BTM feeding damage. Thus, we need to amend the BTM detection tip that focuses on “disappearing leaves” to account for damage produced by high populations of early instar caterpillars, as shown below.
Of course, older BTM caterpillars continue to baffle us with their selective leaf-feeding behavior. They commonly fail to consume leaf edges, producing the characteristic “curlicue” symptom which remains an accurate calling card of BTM.
The Future's So Bright, I Gotta Wear Shades
BTM will not cause boxwoods to vanish in a blinding flash. The caterpillars can be effectively managed with a range of well-timed insecticides. Plus, the plants can be pretty forgiving of first-year heavy defoliation if action is taken to reduce the BTM population.
“Rejuvenation pruning” has long been used to reduce the size of boxwoods that have outgrown their site. Boxwoods that have suffered heavy BTM damage can be pruned back in the spring to stimulate new growth and remove overwintering caterpillars. The shrubs should be closely monitored and an insecticide applied if the BTM infestation returns.
Even more significant is the cutting-edge research on using genetics to differentiate and characterize resistant boxwoods that is being conducted by Dr. Theresa Culley (Dept. Biological Sciences, University of Cincinnati). Her research is funded by an HRI grant, and this is the second year of her field trials. Her encouraging results thus far bode well for the future of boxwoods in Ohio nurseries and landscapes.
Learn More About BTM
As noted above, you can learn more about BTM, including effective insecticides that can kill the caterpillars, by downloading printable versions of the OSU Extension three-part fact sheet series on BTM:
1. BTM Background Information: History, spread, and life cycle.
2. Detecting BTM: What can you do?
3. BTM Management Options: What can you do?
REPORT BTM
Ohio:
You can report a suspected BTM infestation online through the ODA’s Ohio Plant Pest Reporter.
Kentucky:
You should contact your county UK Cooperative Extension Office to report a suspected infestation.
Indiana:
You can report suspected BTM infestations to the Indiana Department of Natural Resources by phone or by email.
