Argyresthia thuiella

Arborvitae leafminer damage. Photo: Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org
Scientific Name: 
Argyresthia thuiella
Common Name: 
Arborvitae Leafminer
Growing Degree Days (GDD's): 
150-260 GDD's (larvae); 533-700 GDD's (adult moths), Base 50F, March 1st Start Date (Source: Cornell Cooperative Extension.)
Host Plant(s) Common Name (Scientific Name): 
Northern white cedar (Thuja occidentalis)
American arborvitae (Thuja occidentalis)
Insect Description: 

Caterpillars of this insect are small (approx. ¼ inch long), greenish/red or brown with a dark brown or black head. Pupae are greenish in color, approximately 1/8 inch long, and found inside mined host plant leaves. Adults are light gray moths with brown and black spots and also approximately 1/8 inch in length. Tiny, pinkish eggs are laid in mid-June to mid-July. Eggs darken in color as they mature. Mature caterpillars are found roughly from April to June and fully grown caterpillars overwinter in mined host plant leaves. Pupation occurs the following spring and adults emerge and females lay eggs. Note: in the Northeastern United States, there are at least four different species of leaf miners that attack arborvitae, including Argyresthia thuiella, which is considered to be the most common. Other species include: A. freyella, A. aureoargentella, and Coleotechnites thujaella (Johnson and Lyon, 1991).

Damage to Host: 

Holes created by the larvae entering the leaves of arborvitae are too small to view without magnification. Young, newly hatched larvae do not cause much noticeable damage. As time progresses, larger larvae are capable of causing more damage. Browning of the plant foliage caused by the damage this insect creates is not typically noticeable until January or February and may sometimes be confused for winter injury. Browned leaf tips that are hollow, sometimes frass-filled, and have entrance holes can be indicative of leafminer presence. If the browned tips are not hollow, the cause of injury may be due to disease, winter injury, or some other factor. Trees may lose up to 80% of their foliage from leafminer attack and still survive. (Johnson and Lyon, 1991)

Monitoring: 

Look for brown tips on arborvitae in the spring and fall. The sunny side of the plant may show damage first. While using magnification, open the discolored tips and determine if they are hollow, frass-filled, or if tiny entrance holes are visible. Caterpillars themselves may be visible from late summer through the next spring. Around June and July, shaking foliage may disturb the tiny, tan colored moths.

Cultural Management: 

When possible to do without damaging the health or aesthetics of the plant, prune off and destroy infested branch tips.

Natural Enemies & Biological Control: 

Many natural enemies have been reported for the Argyresthia spp. leafminers, including A. thuiella. 27 parasites of the larvae and pupae have been reported in Canada. Of those, perhaps one of the most significant is a species of parasitic wasp (Pentacnemus bucculatricis). (Johnson and Lyon, 1991) Unfortunately, some report that these parasites may not be abundant in specimen plants. Schaffner (1959) also reports collecting the following hymenopteran parasitoids from arborvitae leafminer in Wakefield, MA: Apalantes spp., Copidosoma spp., and Microgaster zonaria.

Chemical Management: 

Abamectin (NL)

Acephate (NL)

Acetamiprid (L)

Azadirachtin (NL)

Bifenthrin (NL)

Clothianidin (NL)

Cyantraniliprole (NL)

Diflubenzuron (N)

Dinotefuran (NL)

Emamectin benzoate (L)

Fenpropathrin (NL)

Flonicamid+cyclaniliprole (N)

Gamma-cyhalothrin (L)

Horticultural oil (L)

Imidacloprid (L)

Insecticidal soap (potassium salts of fatty acids) (NL)

Lambda-cyhalothrin (L)

Malathion (L)

Neem oil (NL)

Permethrin (L)

Pyrethrin+sulfur (NL)

Spinosad (NL)

Tebufenozide (larvae) (NL)

Notes: 

Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), diflubenzuron (soil drench), dinotefuran (soil drench), emamectin benzoate (injection), imidacloprid (soil drench), neem oil (soil drench).

Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.

Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: January 2024. To check current product registrations in Massachusetts, please visit: https://www.mass.gov/pesticide-product-registration .