Origin:
This is a native insect in the western U.S.
Biology:
This destructive moth occurs only along the West Coast in California and Oregon. It feeds on a variety of oak trees, but is particularly damaging to Live Oak. There may be up to 3 generations each year when weather conditions permit, and heavy infestations may completely defoliate large oak trees. The moths or larvae can be present from March through November, but their numbers each year vary considerably, with massive outbreaks one year and few larvae on trees in following years. The larva overwinters on the underside of a leaf and resumes activity in the spring. The larvae often leave the foliage to pupate heavily on the trunks of the trees as well as on any hard surface nearby, such as walls of structures.
Identification:
The adult moth has a wingspan of about 1.25 inches and has dull gray wings with darker veins. The male moth has a small yellow patch in the middle of the wing. The flight of the moths is weak and fluttering. The mature larva is about 1 to 1.5 inches long and heavily lined, with a broad yellow band on top with a black line down the middle, and darker lines on the sides with bluish between the lines. The head is disproportionately large and a tan to orange color. The pupa is similar to the chrysalis of a butterfly and will be attached to a surface with silk. It may be tan to yellow in color with black spots on it.
Characteristicts Important to Control:
Most years no control is needed, as the feeding from only a few caterpillars will not threaten the health of the oak trees. Deciduous oaks will replace lost leaves quickly. A great many predatory and parasitic insects and birds feed on the caterpillars and reduce the infestation a great deal. If chemical applications are necessary a labeled contact insecticide can be applied over the foliage of the tree to eliminate the caterpillars present.
