Arborvitae Leafminer—Argyresthia thuiella (Packard)

The arborvitae leaf miner, Argyresthia thuiella, feeds primarily on arborvitae (Thuja spp.). The tiny, silver-to-gray adults, have brown and black markings on their wings and a wingspan of only 3/8 inch. Adults lay eggs on the plants that hatch in 2 to 3 weeks, into 1/8-inch-long yellow-green larvae with a reddish tinge and shiny black head.

After burrowing into the leaf scales, the larvae eat the insides. Damage is apparent from leaf tips, down toward the base. Foliage turns yellow, then brown, and has the appearance of being bleached.

While leafminer damage does not usually kill the plant, aesthetic damage can be significant. Mechanical control (e.g., pruning affected tips) can be effective, and leafminers are highly susceptible to natural enemies, such as parasitic wasps.

arborvitae leafminer adult
The adult arborvitae leafminer is silver to gray in color, with a wingspan of only 3/8 inch.

arborvitae leafminer larvae
Arborvitae leafminer larvae are only 1/8-inch long, and attack plants by burrowing into the leaves.

arborvitae leafminer damage
Damaged plant foliage has a bleached appearance. Note the tiny hole (marked by the white arrow), made by adults in the spring, allowing them to exit from inside the leaf.

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[Photos, left to right: Bruce Watt, University of Maine,; John A. Weidhass, Virginia Polytechnic Institute and State University,; Bruce Watt, University of Maine,]