Another Pest is On the Horizon

Cydalima perspectalis, sometimes known as the box tree moth, is established in Canada and was recently found in the U.S. Feeding by this moth can devastate boxwood plants, which are commonly planted in landscapes across the country. A new review highlights the life cycle and potential impact of this pest and makes recommendations for scouting and management. (Photo by Szabolcs Sáfián, University of West Hungary, Bugwood.org)

By David Coyle, Ph.D.

David Coyle, Ph.D.

Shaped into hedges, balls, cylinders, and any other shape imaginable, boxwoods (species in the genus Buxus) are some of the most ubiquitous and hearty landscape shrubs around. So many boxwood bushes are planted in landscapes that you might not even notice them—until those dark green, compact plants are gone, of course. Then people notice.

One of the biggest threats to boxwoods is Cydalima perspectalis, colloquially called the box tree moth. Several colleagues and I review the biology and management of C. perspectalis in a new article published this week in the open-access Journal of Integrated Pest Management. This pest, native to eastern Asia, has been making its way across the globe via accidental introductions, likely on landscape plants. It has been consuming Buxus and other species throughout Europe and most recently North America, where it was discovered near Toronto, Ontario, in summer 2018.

Cydalima perspectalis larvae consume boxwood foliage and leave webbing on the leaves. With multiple generations per year, high populations can strip boxwoods to the leaf veins and cause plant mortality. Shown here are various forms of damage C. perspectalis larvae can cause, ranging from partial to severe defoliation. (Photos A and D by Alex Rimmer, B and C by Jen Llewellyn, originally published in Coyle et al 2022, Journal of Integrated Pest Management)

Once Canadian regulatory officials discovered this infestation (with the help of citizen science—it was reported on iNaturalist!), they launched a comprehensive and effective monitoring and management program. As C. perspectalis adults appear similar to other native moth species, accurate identification is critical. The larvae, however, are quite distinct in that they consume boxwood foliage and leave webbing on the leaves. High populations can strip boxwoods to the leaf veins and cause plant mortality. With multiple generations per year, these caterpillars can really wreak havoc on a boxwood planting.

In summer 2021, plants infested with C. perspectalis were found in several states in the U.S., including New York, Michigan, Connecticut, and South Carolina. Regulatory action was immediately taken, and as of September 2022 no established populations of C. perspectalis are known. The fact that introductions to several states resulted in no known infestations is a testament to the regulatory officials in those states.

Shown here are pre-adult life stages of Cydalima perspectalis:egg cluster (A), early instar larva (B), late instar larva (C), prepupa (D), pupa 3 days after pupation (E), pupa 9 days after pupation (F). (Photos by Alex Rimmer, originally published in Coyle et al 2022, Journal of Integrated Pest Management)

Ultimately, proper and accurate scouting and prevention is the best defense against this pest. Management can be challenging, but pheromone lures do exist and some effective chemical management methods are available. We know little about biological control options at this point, though several natural enemies will attack this pest.

While the story of C. perspectalis is far from over, there is reason to be optimistic. This is a great example of how citizen science— people reporting things they see— can help discover a new pest. This is also a great example of how fast and thorough regulatory action can be effective in preventing an infestation. And with as much boxwood as we have across the landscape (and the impact it has on the horticultural industry), we’ll all benefit from keeping this pest out of the U.S.

David Coyle, Ph.D., is an assistant professor in the Department of Forestry and Environmental Conservation at Clemson University. Twitter/Instagram/TikTok: @drdavecoyle. Email: [email protected]

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