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.
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Identification and Control Information
- Arborvitae Leafminer (PDF)—Cornell University, Cooperative Extension of Suffolk County
- Arborvitae Leafminer (PDF)—University of Minnesota
- Arborvitae Leafminer (PDF)—North Carolina State University
- Maine Forest Service: Conditions Reports (updated regularly) including annual summary reports
[Photos, left to right: Bruce Watt, University of Maine, Bugwood.org; John A. Weidhass, Virginia Polytechnic Institute and State University, Bugwood.org; Bruce Watt, University of Maine, Bugwood.org]