Pest description and crop damage This insect also is known as the oak ribbed casemaker. The adult moth is mottled white, brown, and black with a wingspread of about 0.33 inch. The mature larvae are about 0.25 inch long and pale yellow to green. Young larvae feed inside leaves, chewing away tissues and leaving a linear mine. Older larvae feed on the underside of leaves, leaving only the upper surface and veins, which turn brown. Severely damaged leaves may be almost transparent. The oak ribbed casemaker is reported on California white (valley) oak (Quercus lobata) and coast live oak (Q. agrifolia).
Biology and life history This insect appears to pass the winter inside its characteristic cocoon. Immature larvae make flat, white, circular cocoons, while cocoons of mature larvae are white with distinctive longitudinal ribs. The latter can be found on leaves, twigs, or other nearby objects. The moths appear in spring and lay eggs on the undersides of leaves. The larvae emerge and feed on the foliage. There are two generations per year.
Natural enemies probably help keep populations in check. Avoid use of broad-spectrum insecticides which kill beneficial insects.
Apply in early summer when caterpillars are first active.
For more information
Johnson, W.T. and H.H. Lyon (1991), Insects That Feed on Trees and Shrubs, 2nd ed., Cornell University Press (p. 220).