• Native to North America.
  • Cedar leafminer complex is a group of insects that feed on cedar foliage, causing a yellowing of the leaves.
  • The group includes:
    • brown cedar leafminer (Coleotechnites thujaella)
    • cedar leafminer (Argyresthia aureoargentella)
    • cedar leafminer (Argyresthia canadensis)
    • arborvitae leafminer (Argyresthia thuiella)

Host species

Cedar leafminers feed on eastern white cedar (Thuja occidentalis).

Characteristics and life cycle

  • Four closely related species feed within the leaves, hollowing out the leaflets.
  • Damage can be seen early in the season and can be confused with winter browning.
  • Adults are small white moths which emerge during June and July.
  • Eggs are laid in July and August and larvae over-winter in leaflets.
  • It is not uncommon to find all four species in a single location.
  • Repeated attacks over several years can cause twig death and sometimes stem death.

Cedar leafminer larvae

Symptoms and damage

  • Leaflets gradually become discoloured, from yellowish to brown in colour.
  • Twigs become bare in the autumn as damaged leaflets fall off.
  • Damaged leaflets can be held up to a light and tiny caterpillars can be seen feeding in the tunnels.

Cedar leafminer damage

Control measures

Ornamental trees may become infested. Twigs can be pruned during the winter to prevent spread.