Larva - The larva is a small, whitish to lemon-yellow maggot up to 3 mm in length (Color Plate 2L).
Pupa- The elongate, 3-mm-long pupa is whitish to dark yellow. Close examination reveals legs and wings appressed to the body surface.
Host Plants - All boxwoods may be infested, but more slowly growing English varieties are less susceptible than American varieties.
Damage - Mining in the foliage, this pest causes the formation of small blisters on the undersurfaces of leaves (Color Plate 2M). Infested leaves usually become yellowish and are smaller than uninfested leaves. As a result, heavily infested plants assume an unthrifty appearance.
Life History - Adult flies insert their eggs into the leaves' upper surfaces. Tiny larvae hatch and mine into the leaves as they feed. The leaves first acquire a water-soaked appearance at the feeding site. Soon, blisters develop on the lower leaf surface; one to several larvae may develop on a single leaf. The leafminers spend the winter in the blisters as larvae. In spring, the blisters develop a translucent "window" through which pupae protrude from the lower leaf surface. Adult flies emerge from the pupae over a 2-week period in early spring shortly after the boxwoods have put out their new growth. The adult flies live only a few days. Only one generation occurs each year.
For specific chemical controls, see the current state extension service recommendations.
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