Box tree moth (BTM) [Cydalima perspectalis (Walker, 1859); Lepidoptera: Crambidae] is a new, invasive species for Ohio. It presents a significant risk to the health of boxwoods (Buxus spp.) in Ohio’s landscapes and nurseries (APHIS, 2022).
Early detection is critical to safeguarding plant health and reducing the economic threat posed by BTM in Ohio. This article provides a pictorial guide of what should be looked for in detecting BTM (Boggs & Stone, 2024).
What to Look For
Striped Caterpillars
As shown in Figures 2 and 3, BTM caterpillars are green to greenish-yellow with black stripes and black dots throughout their development. No native pests specifically defoliate boxwoods in Ohio and only a small number of caterpillars occasionally nip boxwood leaves. Defoliation by a caterpillar points toward BTM (Coyle et al., 2022).
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Strange “Curlicue” Leaf Damage
As BTM caterpillars get larger, they start consuming the entire leaf. However, they often leave behind the leaf edges and sometimes the midvein as shown in Figure 4. The remaining leaf tissue curls to produce a characteristic hair-like curlicue that turns brown (Boggs, 2023, September 27). This unusual damage is easy to spot. Nothing else produces this symptom on boxwoods.
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Silk Webbing
BTM caterpillars are capable of producing silk. They are not, however, heavy silk producers like webworms or tent caterpillars. BTM caterpillars may be found in wispy collections of silk anchoring them to their host (Eshenaur & Leeser, 2024). Their webbing may also entangle feeding debris and frass giving infested boxwoods a tattered appearance.
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BTM caterpillars pupate on their boxwood host. Before pupation, the last instar caterpillars use silk to wrap themselves in whole live or dead leaves as well as leaf debris. They then spin a loose silk cocoon and pupate. These pupation structures remain evident for some time.
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Frass
Insect excrement is called frass. BTM frass looks like small, light-green to greenish-brown pellets. Frass may collect beneath infested plants (Figure 12) or become trapped in caterpillar silk.
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Boxwood Damage
The signs and symptoms of a BTM infestation change as infestations progress. Early instar caterpillars typically feed by removing the upper or lower leaf epidermis. As shown in Figures 13 and 14, the damage may be difficult to detect, particularly with light infestations.
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Adding to the detection challenge is a tendency for the caterpillars to remain hidden from view by feeding on inner foliage during the early stages of an infestation. The boxwoods shown in Figure 15 appeared to be unaffected by BTM.
However, BTM caterpillars were revealed to be feeding on the Figure 15 bushes by parting their canopy as shown in Figure 16. This “inside-out” feeding behavior means light infestations may be hidden from view within the canopy, resulting in the boxwoods appearing normal.
Under high population conditions, the inside-out transition occurs quickly. Figure 17 shows boxwoods in a heavily infested landscape with caterpillars moving from inner to outer foliage.
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Figure 18 shows boxwoods in the same landscape as the boxwoods in Figure 15. The voracious feeding by BTM caterpillars produced brown foliage throughout the canopy. If the caterpillars are left unchecked, the damage can occur quickly in heavily infested landscapes with boxwoods turning from green to brown in a few weeks.
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A close examination will reveal mostly debris with few leaves on the ground. This separates BTM damage from winter injury or fungal infections (Boggs, 2023, July 17). Environmental damage and disease symptoms do not include disappearing leaves.
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BTM caterpillars may also consume the bark and phloem on small twigs (Sisk et al., 2022). This usually occurs in heavy infestations after the caterpillars have consumed all the leaves. Bark damage reduces the capacity for shrubs to recover by sprouting new growth and leaves from buds. Heavy, continual leaf loss and stem damage from BTM throughout the growing season may kill boxwood plants.
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Adult Moths
BTM adults are small moths with a wingspan of 1–1 ½ inches. There are two color morphs. The most common form has wings that are white and edged in gray to grayish brown. Occasionally, the white portion of the wing is tinged with purple as shown in Figure 25. In about 5% of adults, the wings are solid brown. On the forewings of both forms, white spots which some describe as crescent moons distinguish it from other similar species (Gutue et al., 2014).
BTM adults fly at night. This makes it difficult to see them flying around Ohio landscapes. Their similarity to other species means using observation of BTM adults to detect an infestation is much less possible compared to observing the caterpillars and their damage to boxwoods.
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However, the chemical attractants (pheromones) produced by female BTM moths to attract and mate with male moths has been synthesized. The synthetic pheromones are used in traps to detect BTM infestations (Santi et al., 2015; Cook et al., 2022).
Eggs
Clusters of BTM eggs are laid by BTM females on the underside of boxwood leaves with newly laid green eggs changing to greenish-yellow as they mature (Coyle et al., 2022). Although the eggs are distinctive, the clusters are small and difficult to spot; particularly the newly laid green eggs. Again, observing the eggs is not as dependable in detecting new infestations compared to observing the caterpillars and their damage.
Additional Resources
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, July 17). Re-visiting Volutella and Browned boxwoods. Buckeye Yard and Garden OnLine (BGYL).
bygl.osu.edu/node/2198
Boggs, J. (2023, September 27). 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. (2024). Box tree moth (BTM) update #1. Buckeye Yard and Garden OnLine (BGYL).
bygl.osu.edu/node/2335
Cook, J. C., Culliney, T., Funaro, C. F., & van Kretchmar, J. B. (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
Coyle, D. R., Adams, J., Bullas-Appleton, J., Llewellyn E. J., A. Rimmer, A., Skvarla, M. J., Smith, S. M, & Chong, J. H. (2022). Identification and management of Cydalima perspectalis (Lepidoptera: Crambidae) in North America. Journal of Integrated Pest Management, 13(1), 1–8
doi.org/10.1093/jipm/pmac020
Eshenaur, B., & Leeser, J. (2024). Box tree moth (Cydalima perspectalis) [Fact sheet], Cornell College of Agriculture and Life Sciences (CALS), New York State Integrated Pest Management.
cals.cornell.edu/new-york-state-integrated-pest-management/outreach-education/fact-sheets/box-tree-moth
Gutue, C., Gutue, M., & Rosca, I. (2014). Crambidae associated with parks and ornamental gardens of Bucharest. Scientific Papers, Series B, Horticulture, 58, 323–326.
horticulturejournal.usamv.ro/pdf/2014/art54.pdf
Santi, F., Radeghieri, P., Sigurta, G. I., & Maini, S. (2015). Sex pheromone traps for detection of the invasive box tree moth in Italy. Bulletin of Insectology, 68(1), 158–160.
bulletinofinsectology.org/pdfarticles/vol68-2015-158-160santi.pdf
Sisk, E., Brindley, J., & Del-Pozo, A. (2022). Box tree moth in the United States (ENTO-525NP) [Fact sheet]. Virginia Cooperative Extension.
pubs.ext.vt.edu/content/pubs_ext_vt_edu/en/ENTO/ento-525/ento-525.html