Box tree moth (BTM) [Cydalima perspectalis (Walker, 1859); Lepidoptera: Crambidae] is a new, invasive species for Ohio. It is a non-native pest of boxwood (Buxus spp.) in Europe and North America and poses a risk to the health of boxwoods in landscapes and nurseries (APHIS, 2022).
Range and Spread
BTM is native to the same wide geographical range occupied by Asian boxwoods which extends from the Korean peninsula across China into eastern India. BTM is not considered a significant pest of Asian boxwoods (Gao, 2024) likely in part due to native natural enemies of BTM keeping populations in check (Wan et al., 2014). Additionally, Asian boxwoods coevolved with BTM—which has a narrow host range—and thus are likely to carry defensive traits against this defoliator.
BTM was accidentally introduced into Europe and first discovered in Germany in 2007 (Haddad et al., 2020). It quickly spread across the continent ravaging native European boxwoods (Bras et al., 2022).
The rapid spread of BTM across Europe was likely supported by an abundance of susceptible boxwoods coupled with the lack of natural enemies (Mitchell et al., 2018). The native European boxwoods did not co-evolve with BTM, so it is unlikely the native boxwoods had developed defenses against the non-native BTM (Nacambo et al., 2014).
BTM was introduced unaccompanied by natural enemies from its native range in Asia and, without the population suppression provided by predators, parasitoids, and/or pathogens, BTM populations expanded unchecked. This “enemy release” has been observed and documented with other non-natives (Brian & Catford, 2023).
European boxwoods also naturally and commonly occur in wooded areas between urban sites in which boxwoods were frequently planted as ornamentals in Europe. The wild boxwoods served as BTM “pathways” between urban centers, facilitating the insect’s rapid spread (Seehausen et al., 2024).
BTM was first detected in North America in 2018 in St. Catherines, Ontario, Canada, near Toronto (Mally & Nuss, 2010). In 2021, the invader was confirmed in Niagara County, New York, near the Canadian border (New York State Department of Agriculture and Markets, 2021).
The subsequent spread of BTM to additional locations in the United States and Canada has been discussed in detail by various authors and in a number of reports (e.g., Coyle et al., 2022; Proxmire, 2024). Currently, BTM is found in Delaware, Massachusetts, Michigan, New York, and Ohio.
BTM was confirmed in two locations in Ohio in 2023 (Boggs et al., 2023; Boggs, 2023). The Ohio Department of Agriculture (ODA) issued quarantine restrictions in early 2024 (Stone & Boggs, 2024). Later in 2024, the ODA in partnership with the USDA Animal and Plant Health Inspection Service (APHIS) issued a compliance agreement aimed at reducing the business impacts for nursery stock producers located within the BTM-regulated areas while at the same time protecting those outside the regulated areas from BTM (Boggs & Stone, 2024).
A key difference between BTM in Europe and BTM in North America is the lack of native boxwoods. No boxwoods are native to North America, and they are not invasive, so they are only found where they have been planted. Thus, there is no sea of boxwoods to facilitate the rapid spread of BTM (Seehausen et al., 2024).
The semi-isolated status of boxwoods in North America may also enhance efforts to contain the invasion. This includes regulatory actions, such as quarantines, implemented to slow the spread of BTM in North America.
A map of the BTM quarantine in Ohio along with other information on regulatory status of this non-native can be accessed by visiting the ODA Box Tree Moth website (agri.ohio.gov/divisions/plant-health/invasive-pests/invasive-insects/btm).
Potential Impact of BTM
T
he ODA estimates the value of the current inventory of boxwoods in Ohio nurseries as between $200 and $300 million (Kenny, 2023). Additionally, in 2019, the value of sales of boxwoods in Ohio was between $12.5 and $15 million which equaled the sales in California (Hall, 2021). The only state with higher sales was Oregon. Thus, BTM could have a significant impact on the state’s nursery industry through the loss of sales coupled with costs associated with pest management.
Although the taxonomy of Buxus remains in flux, according to Niemiera (2018), “There are about 90 species of boxwood from Eurasia, Africa, the Caribbean, and Central America. However, only three boxwood species—Littleleaf Boxwood (B. microphylla), Common Box (B. sempervirens), and Korean Boxwood (B. sinica var. insularis)—and hybrids of these species are used in the nursery and landscape trades.” Niemiera also notes that over 400 Common Box cultivars outnumber the combined number of Littleleaf and Korean boxwood.
Boxwoods have long played a significant role in landscape designs. They are deer-resistant, broad-leaf evergreens with inconspicuous early-season blooms which support pollinators. Boxwoods are exceptionally responsive to shaping and sculpted topiary and have historically had few serious pests in the landscape. Few, if any, woody perennial plants could replace boxwood in form and function.
BTM presents a risk to boxwoods. According to Cook et al. (2022), “In introduced areas where box tree moth has two generations per year, boxwood stands have declined over 95% in eight years or less.” Indeed, BTM is a potential boxwood killer if infestations are allowed to develop and expand unchecked. BTM caterpillars are easy to kill, so their impact can be mitigated if they are suppressed before they cause significant harm.
BTM Life Cycle
Like other moths and butterflies (order Lepidoptera), BTM develops through four stages:
- eggs
- larvae (= caterpillars)
- pupae
- adults
The caterpillars must shed their skins as they grow, and each time the caterpillars molt, they advance into a new instar. Owing to the complete change in body form during the pupal stage, this type of development is called complete metamorphosis.
BTM caterpillars look similar from the beginning to the end of their development. All instars are lime-green and have black head capsules (Figures 7 and 8). Their bodies are covered in short, rigid hairs. First instars have faint dark stripes and the stripes deepen in color with yellow stripes emerging as the caterpillars develop through additional instars.
BTM development is illustrated in Figure 9. According to the literature, BTM caterpillars may develop through six to seven instars (Lopez & Eizaguirre, 2019; Farahani et al., 2021; Coyle et al., 2022). As the caterpillars become larger, they consume more foliage resulting in more damage. Thus, each new instar causes more damage than the previous instar.
The total seasonal damage by a plant-feeding insect also depends on the number of generations per year and the population densities for each generation. Thus, knowing the number of generations is critical for developing and applying effective management programs.
Research in China revealed that BTM may have as many as five generations per growing season depending on the geographical location (Wan et al., 2014). Preliminary evidence suggests that BTM may produce two overlapping generations in Toronto, Ontario, and in Niagara County (Buffalo), NY. (Sisk et al., 2022).
The exact number of generations in Ohio is yet to be determined. Itis important to note that like all insects, BTM is cold-blooded (ectothermic) meaning that the pace of their metabolism, and thus the speed of their development, is influenced by temperature.
Figure 10 provides an example of the potential for summer temperatures to significantly influence caterpillar development. All of the caterpillars in a BTM population in Southwest Ohio during the summer were early-instars as shown on the left panel of Figure 10. Only nine days later, all of the caterpillars were late-instars as shown in the right panel of Figure 10. Weather data collected 13 miles from the site revealed that the average maximum temperature for the nine-day period was 89 degrees Fahrenheit (32 degrees Celsius) and the minimum temperature was 66 F (19 C) yielding an average max./min. temperature of 77 F (25 C).
The Ohio BTM infestations along with the infestation in Delaware are the most southern infestations found thus far in North America. While anecdotal, the photographic examples in Figure 10 suggest developmental rates and thus the number of generations may be different from infestations found further north. This is currently being investigated.
As illustrated in Figure 11, BTM produces a “split generation” with eggs hatching in the fall and caterpillars feeding before overwintering in a specialized structure called a hibernaculum (Figure 12). The caterpillars spend the winter in a physiological deep sleep called diapause (Lopez & Eizaguirre, 2019).
The literature consistently notes that overwintering caterpillars are in the 3rd or 4th instar stages (Nacambo et al., 2014; Lopez & Eizaguirre, 2019; Farahani et al., 2021). However, during the winter of 2023–2024, caterpillars in several locations in Southwest Ohio appeared to be second instars. This discrepancy requires further investigation.
Once the overwintered BTM caterpillars emerge from diapause, they resume their feeding and development through the remaining instars before pupation. The moths produced from this split generation lay eggs to initiate the first full generation of the growing season.
Additional Resources
Download a PDF of this fact sheet.
For more information on the box tree moth, visit Buckeye Yard & Garden Online (bygl.osu.edu).
References
Animal and Plant Health Inspection Service (APHIS). (2022). Pest alert: Box tree moth (Cydalima perspectalis). U.S. Department of Agriculture.
aphis.usda.gov/sites/default/files/alert-box-tree-moth.pdf
Boggs, J. (2023). Box tree (Boxwood) moth: New detection, what to look for, and management. Buckeye Yard and Garden OnLine (BGYL).
bygl.osu.edu/node/2262
Boggs, J., Stone A., & Kulhanek A. (2023). Box tree (Boxwood) moth confirmed in Southwest Ohio. Buckeye Yard and Garden OnLine (BGYL).
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Boggs, J., & Stone, A. (2024). USDA APHIS releases new box tree moth quarantine and compliance Information. Buckeye Yard and Garden OnLine (BGYL).
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Bras, A., Lombaert, E., Kenis, M., Li, H., Bernard, A., Rousselet, J., Roques, A. & Auger-Rozenberg, M.A. (2022). The fast invasion of Europe by the box tree moth: an additional example coupling multiple introduction events, bridgehead effects and admixture events. Biological Invasions, 24(12), 3865–3883.
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Brian, J. I., & Catford, J. A. (2023). A mechanistic framework of enemy release. Ecology Letters, 26(12), 2147–2166.
Cook, J.C., Culliney, T., Funaro, C.F., van Kretchmar, J.B. & Halberg, R. (Ed.). (2022). New pest response guidelines: Cydalima perspectalis, box tree moth. U.S. Department of Agriculture, Animal and Plant Health Inspection Service.
aphis.usda.gov/plant_health/plant_pest_info/box-tree-moth/box-tree-moth-nprg.pdf
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New York State Department of Agriculture and Markets (2021). NYS Department of Agriculture Confirms Box Tree Moth Found in Western New York.
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