Forest Pests: Insects, Diseases & Other Damage Agents

Arborvitae Leaf Miner
Argyresthia thuiella Packard

Hanson, T., and E. B. Walker. [n.d.] Field guide to common insect pests of urban trees in the Northeast. Waterbury, VT: Department of Forests, Parks and Recreation.

Lepidoptera: Argyresthiidae Hosts: Northern white cedar Evidence: Look for foliage that turns gradually from yellow to brown (a), usually first evident where exposed to full sun. Discolored tips contrast sharply with the surrounding green foliage in the fall and even more so in the spring. From late summer to the following spring, break them open to look for tunnels, larvae, or frass (b). Also look for small holes made by emerging adults. Shake the foliage in June and July to detect the small, light tan moths. Life Cycle: There is one generation per year. Adults appear from June to mid-July. Soon after emergence, the female deposits 1 to 25 eggs under the edges of the current year's leaves. Larvae first appear toward the end of June and immediately mine into the leaves to feed and develop for the rest of the season. In the fall, the larva pushes all of its excrement to one end of its tunnel and overwinters. The frass is ejected from the tunnel in the spring, and the tunnel is extended towards the interior of the crown. Larvae pupate in the mine, and adults emerge shortly thereafter.

a. Mining by ARBORVITAE LEAF MINER results in brown, hollowed out foliage.

b. Break open the brown tips to look for tunnels, larvae, and excrement of the ARBORVITAE LEAF MINER.

Management: These miners are most attracted to older, slow-growing trees that are exposed to sunlight. Severely injured trees will often produce new foliage later in the growing season. However, heavy defoliation over consecutive years can lead to tree mortality. Because parasites of this leaf miner are so abundant and effective as a natural control, artificial control is seldom necessary except on ornamental trees. Then, insecticides can be used at 3-week intervals between early June and mid-July to control females before they lay eggs.

Similar Species: The arborvitae leaf miner described here is generally the most common species. Several related moths, including A. aureoargentella and Pulicalvaria thujaella, are also leaf miners on arborvitae. Their life cycles and appearance are similar, but they differ somewhat in adult emergence and other aspects of their life cycles.

References:

Drooz 1985, p 140; Johnson and Lyon 1991, p 42-43; Martineau 1984, p 106-109; Rose and Lindquist, 1980, p 69-71.

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