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DESCRIPTION
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.
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