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Be On the Lookout for the Box Tree Moth

The box tree moth, Cydalima perspectalis, is a non-native moth that has recently been found in a nursery in South Carolina. Native to eastern Asia, the box tree moth has been present in Canada since November 2018. From August 2020 through May 2021, infested boxwood (Buxus sp.) plants were inadvertently shipped from a grower in Canada to several nurseries in the U.S.; a retail nursery in South Carolina received infested plants in May 2021. As of June 1, 2021, the South Carolina detection is being treated as a regulatory incident, and this pest is not thought to have escaped into the landscape. Clemson’s Department of Plant Industry is investigating plant shipments into and out of the South Carolina nursery to determine if infested material may have been inadvertently sold to homeowners and will be monitoring in and around the nursery to ensure this moth has not escaped. If populations are found, a survey and eradication effort will follow.

Adult moths have white wings with a brown border but occasionally may be the “dark form” that has brown wings. Both color forms have small white comma-shaped spots on the forewing.

Figure 1. Box tree moth adults come in light (left) and dark (right) color phases. Photo by Cosmin Manci (http://lepidoptera.nature4stock.com/?page_id=1236).

Figure 1. Box tree moth adults come in light (left) and dark (right) color phases. Photo by Cosmin Manci (http://lepidoptera.nature4stock.com/?page_id=1236).

Eggs are pale yellow, laid in small groups, and overlap like shingles. Caterpillars primarily feed on boxwood but may also feed on Ilex and Euonymus species. Further, there is some evidence that the caterpillars will feed on Acer sp., Fraxinus sp., Rubus sp., Ligustrum sinense, Eriobotrya japonica, Murraya paniculata, and Smilax excelsa when boxwoods are not readily available. Feeding by young larvae causes leaves to turn brown, but older larvae will consume the entire leaf except for the midvein. While several insects can be pests on boxwoods, the box tree moth is potentially the most impactful as feeding by the caterpillars can cause severe damage and even death to infested plants. Larvae may also produce copious amounts of webbing on infested plants. Caterpillars don’t make distinct cocoons; rather, pupae are found among the webbing and damaged leaves. Several generations may occur in a single year.

Figure 2. Box tree moth caterpillars are greenish-yellow, with white, yellow, and black stripes, a black head, and dark raised spots along their backs. Photo by Cosmin Manci (http://lepidoptera.nature4stock.com/?page_id=1236).

Figure 2. Box tree moth caterpillars are greenish-yellow, with white, yellow, and black stripes, a black head, and dark raised spots along their backs. Photo by Cosmin Manci (http://lepidoptera.nature4stock.com/?page_id=1236).

Figure 3. Feeding damage by young box tree moth caterpillars causes leaves to turn brown, while feeding by older larvae results leaves only brown curled leaf midveins. Photo by Ferenc Lakatos, University of Sopron, Bugwood.org.

Figure 3. Feeding damage by young box tree moth caterpillars causes leaves to turn brown, while feeding by older larvae results leaves only brown curled leaf midveins.
Photo by Ferenc Lakatos, University of Sopron, Bugwood.org.

Figure 4. Larvae often produce large amounts of webbing that can cover the foliage of infested plants. Photo by Colette Walter, http://www.lepiforum.de/webbbs/images/forum_2/pic13983.jpg.

Figure 4. Larvae often produce large amounts of webbing that can cover the foliage of infested plants.
Photo by Colette Walter, http://www.lepiforum.de/webbbs/images/forum_2/pic13983.jpg.

There are no official management recommendations for box tree moth because this is the first time it has been found in the U.S. Small caterpillars can be knocked off plants with a strong stream of water, and several readily available horticultural oils and insecticides are likely to provide effective control. Several natural enemies are likely to help control moth populations.

Homeowners are asked to report any potential occurrence of box tree moth to Clemson’s Department of Plant Industry by calling 864-646-2140 or emailing plantindustry@clemson.edu. It is extremely important to find any infestations early so they can be quickly eradicated before establishing in the environment.

Authors: David Coyle (Department of Forestry and Environmental Conservation, Clemson University), Twitter and Instagram: @drdavecoyle; Steven Long, Department of Plant Industry, Clemson University

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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