Maple Prominent

The Maple Prominent (Latin: Exaereta ulmi) belongs to the Notodontidae family of moths. This species is nocturnal, characterized by a brownish-grey coloration that serves as perfect camouflage against the bark of host trees.

The larvae, or caterpillars, are known for their distinct patterns and size. They can grow to several centimeters in length, often exhibiting longitudinal stripes that help them blend into the foliage during the day.

Adult moths feature a wingspan of approximately 40–50 millimeters. Their forewings have complex patterns of dark lines that mimic wood grain, allowing them to remain inconspicuous while resting on trunks.

Their life cycle is strictly tied to maple trees, which serve as their primary food source. The biology of the species ensures that the larvae mature precisely when the leaves are at their most nutrient-dense stage.

The pupal stage occurs in the soil or under leaf litter. This dormancy allows the insect to survive the winter and emerge as an adult when environmental conditions are optimal.

The primary hosts for the Maple Prominent are various species of maple (Acer). In outbreak years, the damage caused by the larvae can be devastating to local maple populations.

Initial damage involves the skeletonization of leaves, where young larvae consume the soft tissue between the veins. This makes the foliage appear lace-like before it eventually withers and falls off.

Mature larvae are capable of consuming entire leaves, leaving only the stalks. High concentrations of caterpillars can lead to total defoliation, leaving the branches bare in mid-summer.

Continuous defoliation stresses the tree, significantly reducing its photosynthetic capacity. This depletion of stored energy leaves the tree vulnerable to secondary pests and fungal infections.

In ornamental urban settings, severe infestations reduce the aesthetic value of maple trees and can lead to crown dieback, especially if the infestation recurs over several consecutive years.

The Maple Prominent typically completes one generation per year. Its life cycle is perfectly synchronized with the seasonal growth of its host trees.

Adult moth flights usually occur from late May through June. These moths are attracted to artificial lights during the night, which can be used to track their local population density.

After mating, females lay eggs on the undersides of maple leaves. The larvae hatch shortly thereafter, entering their most active feeding phase between late June and August.

Once the larvae reach maturity, they descend from the canopy to the ground. They burrow into the topsoil or leaf litter to pupate, where they remain throughout the autumn and winter months.

Consequently, the most effective time for monitoring the pest is during the height of summer, when larval feeding is most evident and the impact on the foliage is easiest to identify.

One of the earliest signs of an infestation is the appearance of skeletonized leaves in the upper canopy, which gradually progresses downward as the larvae grow.

The presence of frass (caterpillar excrement) on leaves or on the ground beneath the tree is a clear indicator that a colony of larvae is actively feeding above.

Observing the undersides of leaves can reveal small egg clusters or early-instar larvae that feed gregariously during the initial stages of their development.

Thinning of the crown and an overall "see-through" appearance of the tree foliage in mid-summer are major symptoms of heavy infestation levels.

If you see large, distinct caterpillars resting on branches or foliage, it is likely the Maple Prominent, especially if they show a defensive reaction to touch.

Mechanical control includes the removal and destruction of leaf litter in autumn to eliminate overwintering pupae and manually picking caterpillars off young, accessible trees.

Biological control methods are highly effective and environmentally friendly. Applying products containing Bacillus thuringiensis can specifically target the larvae without harming beneficial pollinators.

Chemical intervention with systemic or contact insecticides may be necessary during severe outbreaks, specifically when larvae are in their early stages of development.

• Utilizing light traps to monitor and potentially reduce adult moth populations.
• Encouraging natural predators like birds and parasitic wasps that feed on caterpillars.
• Maintaining tree health through proper watering and fertilization to improve resistance.

Regular visual inspections of maple stands are crucial for early detection. Taking action before the infestation becomes widespread is the best way to protect your trees.