Caterpillars rolling leaves of sugar maples and basswoods were detected in Becker County north of Detroit Lakes while inspecting North American Maple Project plots for early defoliation. The maple-basswood leafroller, Cenopis pettitana has occurred in epidemic numbers on sugar maples and basswood in parts of southern Ontario and other parts of southern Canada recently. There is one generation per year and the eggs overwinter on the tree and hatch in early spring. The young larvae feed initially in the swollen buds but, later in May and June, older larvae construct conical leaf rolls from which they emerge to feed on surrounding foliage. The adult moths emerge from late June to early August. The females lay eggs singly on twigs and small branches.
Green ash leaf defoliation by the black-headed ash sawfly, Tethida barda, was observed in southern Clearwater County. Larvae have blackheads with green to yellowish-white bodies. The larvae feed gregariously in groups of four to twenty, often lined up in rows feeding side by side. Young larvae chew holes in the leaflets, and older larvae eat entire leaflets. Heavily infested young trees may become completely defoliated in one to two weeks. Older trees may become so ragged that most of the leaves drop prematurely. Mature larvae drop to the ground where they make earthen cocoons to spend the rest of the summer, fall and winter. Usually natural enemies keep sawfly populations low, however, repeated defoliations of smaller trees can severely stress trees leading to crown mortality and even death.