The oak skeletonizer, a native species, feeds on the leaves of oaks and chestnut, but shows a preference for red oak. It occurs from southern Canada and the Lake States to North Carolina and Mississippi, the same as the range of the host oaks. The adult moths have a wingspan of 7 to 8 mm; the forewings are largely blackish with some paler areas in them. The larvae are yellowish green and when mature are 5-6 mm in length. When the larvae are disturbed, they spin down from the foliage on a silken thread and seem to hang in mid-air. These suspended larvae are a nuisance when the tree is located over a sidewalk or lawn area. The pupal stage occurs inside a small, 3 mm long, white cocoon which is longitudinally ribbed. The pupa is black and when the moths have emerged it may be seen protruding from the empty cocoons. Small white patches of silk are often seen on the leaves where these insects are present ñ they spin and then use these silken pads as a protective cover under which to molt.
As a result of the feeding of the larvae, the leaves are reduced to their upper surface only, often becoming almost translucent and eventually drying out. Outbreaks occasionally occur causing damage over large areas. Several successive defoliations result in a reduction of growth, and sometimes part of the crown is killed.
Adults emerge from the overwintering cocoons in late April and May and deposit eggs on the undersides, near the mid-vein, of newly expanded oak leaves. The larvae hatch, and at first begin feeding by tunneling in the leaves causing blotch or serpentine mines, but from the third instar on, they feed externally on the lower leaf surface. As a result of this later feeding, leaves appear skeletonized. Depending on population numbers, damage may be slight or even go unnoticed, except in outbreak years. In most of the northeast there are two generations of this insect a year. The second generation adults fly in late July and August, with larvae usually reaching maturity by late October. As the larvae grow and molt, they spin silken pads on the undersides of the leaves under which the molting change occurs. After several molts, the larva spins a characteristic white, ribbed cocoon on leaves, branches, twigs, or nearby objects.
Populations of the oak skeletonizer vary greatly from year to
year, indicating that natural factors such as predators, parasites or
weather may influence them.
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