AROUND THE INDUSTRY
NCDA&CS Spotlight:
The Box Tree Moth
Steve Troxler, Commissioner
By Amy Michael, NCDA&CS – Plant Industry Division, Cooperative Agricultural Pest Survey Coordinator
Boxwoods (Buxus spp.) are one
of the most popular garden plants in the world, with records of ornamental boxwood plantings as early as 4000 BC (NCCE). Planted as hedgerows and in parks and gardens practically everywhere, with species and varieties ranging in tolerance from tropical climes down to USDA Zone 4, the boxwood is a very lucrative nursery plant. In the United States alone, an estimated 3.6 million boxwoods are produced each year, with North Carolina ranking No. 7 for production (Frank, 2021). However, every plant has its share of vulnerabilities, and the ubiquity of boxwoods in the landscape has turned the box tree moth into a wellfed, prolific pest capable of destroying whole stands of boxwoods in areas where the insects have been introduced. For that reason, it is critical for North Carolina landscapers, nursery resellers and boxwood producers to understand the background of this pest and prepare to prevent it from becoming a major problem in our state.
Impact and Invasion History
The box tree moth (Cydalima perspectalis, BTM) is a defoliating pest of boxwoods, though it will also eat new bark growth once it has depleted the leaves. BTM can produce up to five generations per year in favorable field conditions, meaning populations can grow to explosive numbers in just one season. Heavy infestations can lead to complete destruction of established boxwood stands if left untreated (Figure 1). And while Buxus is by far the most preferred host of BTM, other popular landscape shrubs are also at risk. According to a 2023 U.S. Department of Agriculture review of BTM literature, they “consider it likely 26 NURSERY & LANDSCAPE NOTES || FALL 2023
Figure 1. A healthy boxwood (top) compared to one heavily infested with box tree moth caterpillars (bottom). USDA photos by Ignacio Baez (top) and Mafalda Weldon (bottom).
that Murraya paniculata [orange jasmine] is a host of the BTM, and Euonymus alatus and E. japonicus are possible hosts. Ilex purpurea [oriental holly] is unlikely to be a host, and many other plant species mentioned in the literature seem to only have served as refugia after all boxwood leaves and bark in the vicinity had been consumed.” (USDA-APHIS-PPQ: Plant Pest Risk Analysis, 2023). This point has further implications for nursery dealers:
While BTM has only been observed to complete its life cycle on Buxus and the three other species mentioned above, there is still the risk of caterpillars crawling to adjacent plants to pupate — meaning that they could hitchhike in otherwise innocuous plant shipments coming into our state. Originally native to eastern Asia, BTM was first found in Germany and the Netherlands in 2007 and may have been introduced through infested plant shipments. Europe has several naturally occurring Buxus spp. in addition to ornamental plantings, and the moth quickly spread throughout the European Union, Britain and Ireland. To date, BTM has spread to an estimated 30 European countries (Canadian Food Inspection Agency, 2019). BTM eventually made a transatlantic voyage and was discovered in a Toronto neighborhood in 2018. The Canadian Food Inspection Agency (CFIA) has surveyed for this moth ever since, and soon found populations in Windsor (near the border with Detroit, MI) and in St. Catherine’s (near the border with Niagara Falls, NY). Unfortunately, Niagara Falls poses no challenge to a winged organism, and the first U.S. detection of BTM was made in Niagara County, NY, in 2021, likely arriving by natural spread. BTM has now spread further south by hitchhiking along with humans, and was found in southeastern Michigan in 2022 and in southwestern Ohio and the Cape Cod region of Massachusetts in 2023. Canada has also continued to survey, finding BTM at several retail locations in Quebec, New Brunswick, Nova Scotia, Prince Edward Island, and Newfoundland and Labrador in 2023 — the first instances in which the pest has been found in Canada outside of Ontario. The CFIA has enacted a quarantine on host plants within infested areas (Canadian Food Inspection Agency, 2019).
