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Archive for September 26, 2016

Maple Leafcutting Moths

9-26-16-maple-leafcutting-moth-larva-20160910_7437Have you ever noticed one or more oval-shaped holes in a Sugar Maple leaf and wondered how they got there? These leaf particles were cut out by the larva of a Maple Leafcutter Moth. Emerging in June from the ground where it overwintered as a pupa, the metallic blue adult moths mate and females lay eggs, mainly on Sugar Maple leaves, but also occasionally on other maples, birches, American Beech and other hardwoods. When the eggs hatch, the larvae make small lines in the leaf, as they mine for food in between the upper and lower surfaces of the leaf for the first two or three weeks of their lives.

As summer progresses, the growing larva moves to the surface of the leaf and begins cutting small oval-shaped pieces of the leaf and using them as shelter. It constructs portable cases, fastening the leaf disks together with silk. The larva resides inside this case, with its head poking out far enough to feed on a leaf. If you see holes in a leaf, you will probably also see small brown rings with green centers created as the larva feeds around the edges of its case. Sometimes the center of these feeding rings fall out, also leaving oval holes in the leaf.

As the Maple Leafcutter larva grows, it molts and after each molt it cuts new, larger disks from the leaf to add to its case. By the end of the summer, the case consists of multiple leaf disks. In September, the moth larva drops or crawls down the trunk of the tree to the ground, spins a cocoon and pupates.

Maple Leafcutter Moths can cause browning of foliage, usually in scattered small areas. Occasionally extensive areas are hit hard (during the mid-1970’s approximately 40,000 acres were affected in Vermont) but research shows that three years of complete defoliation by this insect are required to significantly reduce the starch content of maple roots (an indication of physiological stress).

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