The orangestriped oakworm is a native insect found in the eastern United States. This insect is often found associated with closely related caterpillar species feeding on oak, including the spiny oakworm (A. stigma), the pinkstriped oakworm (A. virginiensis) and the greenstriped mapleworm (Dryocampa rubicunda). The orangestriped oakworm is over 2 inches long when caterpillars are fully mature. Mature larvae are black with orange longitudinal stripes. Caterpillars crawl out of their host trees at maturity (typically by September) and burrow 2.5-10 cm into the soil where they will pupate and overwinter. This happens in a cell below ground. Moths will emerge the following summer and are often found attracted to lights at night. Adult moths range from pale orange (females) to darker rusty orange (males) and possess a single white spot on each forewing. Females are slightly larger with wingspans of up to 2 inches, with males reaching approximately 1.5 inches. Adult female moths take approximately one month to lay up to 500 eggs (bright yellow when first laid) on the undersides of oak leaves. Eggs are usually laid on the lower branches and when they hatch, caterpillars feed gregariously (in groups) and skeletonize the oak leaf, leaving behind only leaf veins. Young caterpillars are greenish-yellow with two horn-like projections on their 2nd thoracic segment. Mature caterpillars are capable of defoliating individual branches, eating every part of each leaf except for the midvein. In the northern parts of this insect's range, a single generation occurs per year. Historically, outbreaks of this insect have occurred. Forested oaks are often most impacted, but shade trees in urban environments or parks may be fed upon during these outbreaks as well.
Young larvae feed in groups and skeletonize their host plant leaves, leaving behind only as lacework of leaf veins. Older larvae are capable of eating the entire leaf, leaving behind only the midvein and defoliating branches one at a time. Historically, outbreaks have occurred in New England resulting in thousands of acres of defoliation by this native insect. Otherwise healthy host plants can tolerate a single year of defoliation. However, repeated seasons of defoliation by this insect, or feeding by orangestriped oakworm combined with additional stressors may harm the trees.
In the summer, visually scout for skeletonization occuring on oak leaves or other host plants. The orangestriped oakworm is not the only insect that causes this type of damage on oak, so observation and identification of the caterpillar life stage will need to be made to confirm what insect is causing the damage. If orangestriped oakworm is known to be currently experiencing a population outbreak, traps with black lights can be used at night to detect flying adult moths and estimate the local population or plan management of the caterpillars.
If clusters of young, newly feeding larvae (found in groups) are seen, they can be removed and destroyed, particularly on smaller trees. If this is done before the caterpillars mature and can do their most significant feeding, it may help reduce the defoliation on a single plant.
Because the orangestriped oakworm is a native insect, there is a complex of diseases, parasitoids, and predators that keep the populations of this insect in check. Pupal parasitoids and diseases include: Cratichneumon w-album, an ichneumonid wasp parasitoid that may kill approximately 10% of pupae each year; disease caused by Cordyceps militaris as well as a reported virus kills approximately 14% of the pupae each year; and a tachinid fly (Winthemia datanae) that kills 16-42% of the pupae each year (Hitchcock, 1961). Egg parasitoids include Trichogramma and Tetrastichus spp. parasitoid wasps that can parasitize 22-74% of the eggs of the orangestriped oakworm (Hitchcock, 1961).
Acephate (NL)
Acetamiprid (L)
Beauveria bassiana (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorantraniliprole (NL)
Chlorpyrifos (N)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Deltamethrin (L)
Emamectin benzoate (L)
Flonicamid+cyclaniliprole (N)
Tau-fluvalinate (NL)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Indoxacarb (L)
Insecticidal soap (NL)
Lambda-cyhalothrin (L)
Malathion (L)
Neem oil (NL)
Pyrethrin+sulfur (NL)
Spinetoram+sulfoxaflor (N)
Spinosad (NL)
Active ingredients that may be applied systemically include: acephate (injection), acetamiprid (injection), chlorantraniliprole (soil drench), cyantraniliprole (soil drench, soil injection), emamectin benzoate (injection), and neem oil (soil drench).
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.