Lesser maple spanworm

The Lesser maple spanworm (Itame pustularia) is a moth belonging to the order Lepidoptera and the family Geometridae. It is recognized as a specific forest pest that primarily targets maple trees, making it a subject of significant interest for arborists and forest management specialists.

This species specializes in feeding on various species of the genus Acer, with a strong preference for red maple (Acer rubrum). While localized outbreaks are common, severe infestations can occur, leading to extensive defoliation in both natural stands and urban landscape plantings where maples are commonly used as ornamental trees.

The biological cycle is univoltine, meaning there is only one generation per year. The insect overwinters in the egg stage, typically on the bark or near the buds of host trees. In spring, larvae emerge to coincide with leaf development, feeding voraciously throughout several instars before pupating in the leaf litter or shallow soil.

The primary damage caused by the larvae is the skeletonization and consumption of foliage. Heavy infestations result in significant defoliation, which hampers the tree's ability to store energy for the next growing season. This stress can lead to branch dieback, increased susceptibility to secondary pests, and a general decline in the host tree's overall vigor.

Effective management requires a combination of monitoring and intervention. Scouting for larval activity during early spring is crucial for timely management. Integrated Pest Management (IPM) strategies include the application of biorational insecticides, such as those containing Bacillus thuringiensis, and the preservation of natural predators, including parasitic wasps and predatory beetles, which play a key role in regulating spanworm populations.