The oak skeletonizer is a native species of New England and elsewhere in the eastern United States and parts of Canada. Deciduous oaks and chestnut are hosts for this insect. The adult moth of this species is typically present by late May, with females laying their eggs on the undersides of host plant leaves. Eggs hatch and larvae (caterpillars) feed by skeletonizing the leaf to the extent that it becomes translucent, with only the leaf veins left intact. Pale yellow or green tinted larvae are fully grown when they are approximately 7 mm. in length. If disturbed, the larvae will drop from the tree on a silken thread. Caterpillars spin small, flat webs to molt in between instars. For the last molt of the caterpillar, they will form white, ribbed cocoons on leaves, branches, and twigs within which they will eventually pupate. The insect may overwinter as a prepupa in these cocoons, and eventually pupate the following season prior to emerging as an adult. In the warmer parts of its range, it is possible that this insect has 2 generations per year. Occasionally, this insect has a large outbreak population. For example, in 1971 in New York, trees were damaged by this insect by July and a second generation was found by September. In 1959 and 1960, two generations per year were observed in Michigan (Gibbons and Butcher, 1961).
Foliage of the red oak group is skeletonized by this species. Leaves become translucent and eventually dry out. Heavily attacked foliage will appear lacey from the skeletonizing. Occasional outbreaks can cause damage over a large area, and repeated years of defoliation can cause a reduction in host plant growth. Occasionally, part of the tree crown may be killed by the activity of this insect. However, the oak skeletonizer is often found in low level, non-damaging populations and their presence can be tolerated. In those years, chemical intervention is not necessary.
Visually monitor for the activity of this insect in late May or early June (first generation). Look for skeletonized host plant leaves and eventually the characteristic white, ribbed cocoons.
Rake up fallen, infested host plant leaves and destroy. This will remove the cocoons.
Because of the fluctuation in oak skeletonizer populations from year to year, and collapses following occasional outbreaks, parasites and predators are assumed to be impacting their populations. However, little is known about the specifics regarding these natural enemies at this time. Schaffner (1959) reports the following hymenopteran parasitoids from oak skeletonizer samples collected in Massachusetts and New York: Bucculatriplex bucculatricis, Chrysocharis spp., Cirrospilus cinctithorax, Cirrospilus flavicinctus, Eurytoma solenozopheriae, and Pnigalio maculipes.
Azadirachtin (NL)
Bacillus thuringiensis subsp. kurstaki (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorpyrifos (larvae) (N)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (eggs) (L)
Lambda-cyhalothrin (L)
Neem oil (NL)
Pyrethrin+sulfur (NL)
Pyrethrins+piperonyl butoxide (L)
Spinosad (NL)
Two applications at 10 day intervals may be needed for heavy infestations.
When used in a nursery setting, chlorpyrifos is for quarantine use only.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
