The maple leafcutter is native to the Northeast and parts of Canada. Adult moths are small, steel blue in color, with bright orange heads, and typically emerge in late May. Adults may be attracted to UV and mercury vapor lights. Adult females lay their eggs on the underside of host plant leaves. Newly hatched larvae enter the tissue of the leaf, where they feed by mining for approximately 2 weeks. Following this, they cut and remove two oval pieces from the leaf, to form a case to live in from which it can reach out and skeletonize a circular area around the case. Holes left behind are approximately 0.75 inches in diameter. Caterpillars are capable of moving their cases to a new location on the leaf once all of the surrounding tissue (around the case) has been skeletonized. This type of feeding leaves behind an oval, still green area of leaf tissue that is surrounded by a brown, skeletonized, circular dead area tissue. Caterpillars are 6 mm. in length at maturity, dull white in color, with a brownish head and thorax. As the caterpillar grows, it may need to create a new case that is big enough for it to fit in. Fully grown caterpillars crawl or drop to the ground, where they pupate, by September. During this time, it is possible to see the caterpillars crawling to the ground, dragging their cases with them, especially during high population years.
Foliage, primarily of sugar maple, but also red maple, beech, and birch, especially if near sugar maples may turn prematurely brown as a result of the activity of this insect. Larvae cut out leaf disks and then skeletonize the upper leaf surface, creating a donut-shaped scar. Blotch mines are created in June, and may be difficult to see. Major damage is usually not noticed until late July/August, when the circular holes are apparent in the leaves after the caterpillars create their oval/circular "case". Typically the populations of this insect occur at low, non-damaging levels. Occasionally, the maple leafcutter can be a serious pest. If multiple years of defoliation occur in a row, older host trees may be weakened (after 3 years of defoliation) or (very rarely, even after 7 years of defoliation) killed. Repeated years of feeding by this insect may significantly reduce sap production in sugar maple. However, feeding damage from this insect is typically scattered throughout managed landscapes, insignificant, and not requiring management. Historically, outbreaks of this insect have lead to overflow feeding on additional hosts - for example, Ostrya, Pyrus, Sorbus, Fagus, Quercus, Vaccinium, and Ulmus - however records indicate that only slight feeding on these other species (and no egg laying) occurred when an outbreak on nearby maple was extremely dense (Pohl et al., 2014). Historical outbreaks have occurred annually for periods of 6-8 years in certain locations (Houston et. al., 1990). (Example - 321,000 acres defoliated in Ontario in 1981; 35,000 acres defoliated in Vermont in the 1970's.)
Particularly if a regional outbreak is expected, look for flying adult moths starting in late May. Scout and visually search for blotch mines created by the caterpillars in June. Caterpillars may be difficult to manage once they are feeding within the leaf tissue and protected. Luckily, management of this insect is usually not necessary, as the population is usually below damaging levels.
In forested locations, prescribed burns (not recommended in residential or ornamental landscapes) may be an effective option for maple leafcutter management during severe outbreaks of the insect. In a study in Michigan, leaflitter was burned prior to the spring emergence of the adult moths, to target the overwintering pupae. In one study, adult emergence of the moths was significantly lower in the burned area than in control plots. Pupal mortality was approximately 90%, and higher than the chemical management percentages when the insect was treated for with carbaryl (Simmons et al., 1977).
In ornamental or residential settings, raking up and destroying fallen leaves found around infested trees in the fall may help reduce the population on that specific tree, however the efficacy of this is not fully understood.
Information about the natural enemies of the maple leafcutter is shockingly difficult to find for this native North American insect pest that sometimes outbreaks into a major defoliating species. Clearly, natural enemies of this insect exist in order to (in most years) keep the population below damaging levels on its host plants. Parasitoids in the genus Pnigalio and Closterocerus have been suggested as potentially important natural enemies of pest leaf miners, including the maple leafcutter (Kirkland, 2009). More research may be needed in this area to identify the significant predators, parasitoids, or diseases that limit maple leafcutter populations.
Abamectin (NL)
Acephate (NL)
Acetamiprid (L)
Azadirachtin (NL)
Bacillus thuringiensis subsp. aizawai (L)
Bacillus thuringiensis subsp. kurstaki (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorantraniliprole (NL)
Chlorpyrifos (larvae) (N)
Chromobacterium subtsugae (NL)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Deltamethrin (L)
Emamectin benzoate (L)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Lambda-cyhalothrin (L)
Methoxyfenozide (NL)
Neem oil (NL)
Pyrethrins (L)
Pyrethrins + piperonyl butoxide (L)
Pyrethrin+sulfur (NL)
Spinetoram+sulfoxaflor (N)
Spinosad (NL)
Tebufenozide (NL)
Tau-fluvalinate (NL)
Zeta-cypermethrin (L)
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.
