The oak skeletonizer or oak slugs, a native species, feeds on leaves of oaks, but prefers the Red Oak. It occurs from southern Canada to Mississippi and Texas, the same range as a host of oak trees. The adult moth have a wing span of 7 to 8 mm; the forewings are largely blackish with some paler areas in them. The larvae are yellowish and 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 hang in mid air, and they also have a slightly repulsive odor.
LIFE CYCLE AND INJURY
There are two generations per year. Winter is spent as pupa in white silk cocoons, which are longitudinally ribbed and are deposited on the tree trunks and leaves. The pupa is black and when the moth emerge it may be seen protruding from the empty cocoon. Small white patches of silk are often seen on leaves where these insect are present and these silk pads are used as a protective cover under which to molt. First generation moths emerge in April and May and lay eggs on the undersides near the mid-vein, of newly expanded oak leaves. Newly-emerged larvae feed as miners, by tunneling in the leaves causing blotch or serpentine mines. Later the third instar (full-grown larvae about 1/4 inch long) feed externally on the leaf surface. As a result of their feeding, the leaves are reduced of their surface, (the green tissue only), becoming translucent and the leaves appear skeletonized. Depending on populations numbers, damage may be slight or in outbreak years occasionally occur causing excessive defoliation resulting in reduction of growth and sometimes crown dieback. The second generation adults fly in late July & August, with larvae 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 in leaves. branches, twigs and the tree trunk.
MANAGEMENT and CONTROL
Red Oaks are vulnerable to these insects and repeated attacks may result in weakened trees, dieback and increased susceptibility to attack by wood boring insects and other diseases. Fallen leaves should be rakes and removed or burned to destroy the cocoons. Populations of the oak skeletonizer vary greatly from year to year, indicating the natural factors such as predators, parasites or weather may influence them. All worm larvae (lepidoptera) are highly susceptible to the bacteria based bio-pesticide called Bt. (bacillus thurengiensis). These microbes are only toxic to caterpillars, and won’t harm people, birds dogs, cats, water supplies or beneficial insects. When Bt. is applied as a foliar spray, the Oak Slug eats the microbes, which paralyzes their mouth parts and stomachs. The bacteria then, proceeds to eat the worm from the inside destroying them in two or three days and again this will not hurt the birds if they should eat the worm.