Box tree moth identified in U.S.

Photo by Franz van Duns

The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) has issued a be-on-the-lookout alert for the box tree moth, a destructive pest of one of the industry’s most valuable and prolific crops: boxwood.

In late May, APHIS confirmed the presence of box tree moth, Cydalima perspectalis, in the continental United States and has been taking action to contain and eradicate it. The pest was imported on nursery plants shipped from Ontario, Canada.

The box tree moth can significantly damage and potentially kill boxwood plants if left unchecked. Between August 2020 and April 2021, a nursery in St. Catharines, Ontario, shipped boxwood that may have been infested with box tree moth to 25 retail locations in six states —Connecticut, Massachusetts, Michigan, New York, Ohio, and South Carolina — and a distribution center in Tennessee.

As of July 15, APHIS confirmed the pest had been officially identified in three facilities in Michigan, one in Connecticut, one in South Carolina and one in Ohio. APHIS announced it is working with state plant regulatory officials to determine whether other facilities may be impacted.

In late May, APHIS issued a Federal Order (bit.ly/BTM_Federal_Order) to halt the importation of host plants from Canada, including boxwood (Buxus sp.), euonymus (Euonymus sp.), and holly (Ilex sp.).

APHIS announced it’s coordinating closely with the affected states to:

• Find and destroy the imported plants in the receiving facilities.
• Trace imported plants that were sold to determine additional locations of potentially infected boxwood.
• Provide box tree moth traps and lures for surveys in the receiving facilities and other locations that received potentially infected boxwood.
• Prepare outreach materials for state agriculture departments, industry, U.S. Customs and Border Protection Agriculture Specialists stationed along the Canadian border, as well as the public.

“These immediate measures are focused on protecting the economic viability of the thriving U.S. boxwood industry as well as nurseries and other establishments that sell these plants wholesale and direct to consumers,” according to released statement by APHIS.

Canada has also acted swiftly to stop the spread, according to Jen Llewellyn, nursery and landscape specialist at the Ontario Ministry of Agriculture, Food and Rural Affairs.

“Ontario has increased its intensity of pheromone traps in the area surrounding the new find in Niagara and the existing Toronto surveillance area, as part of an industry-led initiative to delineate the infestation and limit the spread of this pest,” she said in a late June interview. “Quebec and British Columbia are actively using pheromone traps to confirm BTM is not found in these areas, to provide fact-based evidence to support a reconsideration of the USDA-APHIS Canada-wide order.

“Best management practices are being implemented across Canada by nursery growers to ensure host plants are free from BTM at the time of shipping. Based on the Canadian experience, we encourage U.S. growers to monitor for this pest in areas of key boxwood production as an early warning system.”

Identification

Adult bodies are white, with a brown head and abdomen. Wings are white and slightly iridescent, with an irregular thick brown border spanning 1.6-1.8 inches. Some adults have completely brown wings with a small white streak on each forewing.

Eggs are pale yellow and laid in flat clusters on the underside of leaves. As they mature, a black spot appears marking the larval head.

Newly hatched larvae have black heads and are green to yellow. As they age, dark brown stripes develop on the body. Sixth instar larvae are about 1.6 inches long and have thin white and thick black stripes and black dots outlined in white along the length of the body.

Pupae develop inside a silk cocoon and are 0.6-0.8 inches long. They are initially green, with black stripes on the back, and turn brown as they mature.

Damage

The box tree moth can cause heavy defoliation of boxwood plants if populations are left unchecked. Defoliation of existing and new growth can kill the plant. If no foliage is available, larvae have been observed feeding on the bark, which can cause branches or the entire plant to die.

Signs of damage may not appear at the beginning of an infestation because young larvae hide among twigs and leaves. Larvae skeletonize the leaves and feed on the bark, causing defoliation and dryness, leading to the plant’s death. Signs of feeding include green-black frass (excrement) and webbing.

Monitoring

According to APHIS, start delimitation surveys immediately after detecting box tree moth. Depending on the climatic conditions where the moth is detected, two to five generations may occur per year. If no additional detections are made, surveys should continue for at least one year in areas with three or more generations and for two years in areas with two generations. Survey continuously when temperatures are greater than 51°F and adults are flying, typically between May and October.

If moths are detected in the fall in areas where the pest is likely to overwinter, surveys should resume the following spring, based on degree day models for adult emergence.

The most suitable method for detecting and delimiting box tree moth is through the use of pheromone traps. The survey design focuses on trapping in the core area around the initial detection and along the perimeter of the survey area. Visual inspections for box tree moths and damage to host plants can be useful, but some infested plants may not have visible insects or symptoms, depending on the time and severity of infestation.

For delimitation survey design, refer to the box tree moth response guidelines here, https://bit.ly/BTM-pest-response.

Control

APHIS has released a list of insecticides available in the United States for use against box tree moth:

Diamides (Mode of Action [MOA] 28), chlorantraniliprole (active ingredient [AI]); ecdysone Receptor Antagonists (MOA 18), methoxyfenozide (AI); glutamate gated chloride channel blocker (MOA 6), abamectin (AI) and emamectin benzoate (AI); neonicotinoids (MOA 4A), thiacloprid (AI); organophosphate (MOA 1B), trichlorfon/dimethoate/chlorpyrifos (AI); pyrethroids (MOA 3A), λ-cyhalothrin/ß-cyfluthrin/cypermethrin/τ-fluvalinate (AI); and spinosyns (MOA 5), spinosad (AI).

Please refer to the pest response guidelines (https://bit.ly/BTM-pest-response)for more details.

There are some biological control options. Chelonus tabonus, Tyndarichus spp. and Trichogramma spp. are reported to parasitize box tree moth eggs. Bioinsecticides based on Bacillus thuringiensis serotype kurstaki (Btk) have been effective against box tree moth larvae in Europe. Casinaria spp., Compsilura concinnata, Dolichogenidea stantoni, Exorista sp., Protapanteles mygdonia and Pseudoperichaeta nigrolineata are larval parasitoids of box tree moth. In laboratory studies, entomopathogenic nematodes Steinernema carpocapsae and Heterorhabditis bacteriophora caused high mortality of box tree moth larvae. Brachymeria lasus and Apechthis compunctator are pupal parasitoids of box tree moth.

Sources: USDA Animal and Plant Health Inspection Service and reporting by Kelli Rodda