Spotted tentiform leafminer
Phyllonorycter blancardella (Fabr.)
The adult is a tiny beige moth with heavily fringed wings striped with golden brown and white bands (A). Eggs are laid individually on the undersurface of the leaves. The yellowish larva has a dark head and lives inside the leaf (B).
Widespread in most fruit-growing states and provinces in eastern North America.
Apple is the preferred host. The first three larval instars feed on the tissues between the two epidermal layers of the leaf, separating the outer layer of the leaf undersurface from the tissue above and causing a translucent sap-feeding mine that is visible only from the under leaf surface (C). The last two instars feed more extensively on leaf tissues and their tissue-feeding mines appear as clear blotchy swellings (D) on the upper surface of the leaf and gray on the underside with a longitudinal pinch.
The apple blotch leafminer (P. crataegella Clemens), is nearly indistinguishable from the spotted tentiform leafminer, but has forewings that are usually smaller and less heavily marked with white scales (E). P. crataegella is more prevalent in New England than elsewhere, and its hosts include apple, pear, cherry, plum and quince.
Monitor the population with pheromone traps and use a degree-day developmental model to fix the period of 2nd generation mine occurrence; insecticide applications normally not necessary unless mines exceed 1–2 per leaf (check local threshold recommendations). Spur and leaf sampling for sap-feeding mines allows effective timing of spray applications. Selective insecticides allow parasitoids to substantially reduce larval populations.
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