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How to identify it
- The moth is creamy white, heavily dusted with black and brown scales, with a wingspan of about 9 mm. Each forewing carries three oblique blackish bands, a number of dots along the front edge and outer margin, and a shaded tip.[1][2]
- The full-grown larva is only about 3 mm long, reddish with dark legs and a black head, with a dark brown spot on the segment behind the head and another on the last abdominal segment.[1]
- Mined leaflets at the twig tips turn dull yellow and then brown; held up to a light, a damaged leaflet shows the tiny caterpillar in its tunnel.[1][3]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Arborvitae leafminer | The arborvitae leafminer (Argyresthia thuiella) is the other common member of the cedar leafminer complex and makes the same hollowed, discolored tips; the brown cedar leafminer is a gelechiid moth whose pupation and adult emergence come a few weeks later, and its adult is creamy white heavily dusted with black and brown scales.[1][3] |
| Winter browning | Early-season leafminer damage can be confused with winter browning; mined leaflets are hollow and, held to the light, show a caterpillar or its tunnel.[3] |
Where it lives
It occurs from New Jersey to New Brunswick and west to Saskatchewan; Natural Resources Canada gives eastern Canada and the northeastern United States.[2][1]
Biology and life cycle
The hosts are cedars and arborvitae (Thuja), chiefly eastern white cedar; Natural Resources Canada also lists western redcedar. Four closely related leafminers share these hosts and it is not uncommon to find all four at a single location.[1][3]
The moths emerge in June and July, a few weeks after the arborvitae leafminer. Eggs are laid from late June to early August between the scale-like leaves on growing tips. The larvae bore into the leaves and mine along the twigs, feeding until winter, then overwinter inside the mines. Pupation takes place in spring within the mined leaflet; the pupa is brownish green, pointed and curved at the tip. There is one generation a year.[1][2][3]
Damage and signs
Health risk
The sources treat it only as a foliage miner of cedar and mention no effect on people.[1][2][3]
Control
Prevention
Check yellowing tips early in the season by holding leaflets up to a light; hollow leaflets with a tiny caterpillar inside distinguish leafminer damage from winter browning.[3]
Traps and physical control
On ornamental trees, prune out infested twigs during the winter, while the larvae are still inside the mined leaflets, to limit spread.[3][1]
Common questions
- How do I tell brown cedar leafminer from arborvitae leafminer?
- Both mine arborvitae leaflets and are often on the same tree. The brown cedar leafminer pupates and emerges a few weeks later than the arborvitae leafminer, and its adult is a creamy white moth heavily dusted with black and brown scales, about 9 mm across.[1][2]
- When do the moths fly?
- Adults emerge in June and July, and eggs are laid from late June into early August on the scale leaves at the twig tips.[3][1][2]
- Can it kill my arborvitae?
- Heavy, repeated attacks can. The USDA manual says ornamental arborvitae is subject to serious injury, and Ontario records twig death and sometimes stem death after several years of attack.[2][3]
Sources
- Natural Resources Canada, Canadian Forest Service, “Brown cedar leafminer, Trees, insects and diseases of Canada's forests.” tidcf.nrcan.gc.ca/en/insects/factsheet/8328 (accessed 2026-11-10)
- USDA Forest Service, “Eastern Forest Insects, Miscellaneous Publication 1175 (W. L. Baker, 1972; scanned copy).” archive.org/details/easternforestins1175bake (accessed 2026-11-10)
- Government of Ontario, “Cedar leafminer (cedar leafminer complex), forest health fact sheet (updated July 28, 2022).” www.ontario.ca/page/cedar-leafminer (accessed 2026-11-10)
- iNaturalist, “Coleotechnites thujaella taxon page (order and family).” www.inaturalist.org/taxa/217385 (accessed 2026-11-10)