Species: Coleophora ulmifoliella McDunnough [Lepidoptera: Coleophoridae]
This casebearer is a small caterpillar which is a native of North America.
It is most commonly found on American elm though it can cause considerable damage to Camperdown elm.
The larvae fold over the edge of a leaf and cut it off. This forms a tiny case that is about 3/8 to ½ inch long and only 3/32 inch wide. The case what appears as a serrated edge formed form the serrated edge of the leaf. The larvae actually feed by mining leaves from the lower surface which causes brown patches to show on the upper leaf surface.
Description and Life Cycle:
Buff colored moths with gray markings emerge in late July to mate and lay eggs on the leaves of elm. Soon after hatching the caterpillars make small mines in the leaves. After a couple of weeks, the larva emerges from the mine and constructs a case by folding over the edge of a leaf and cutting it off. The larva carries this tubelike case for the rest of its development. From this case, the larva continues to mine patches within leaves. By September, the casebearers are only about half mature when they move to small branches where they firmly attach the case. In May, the larvae construct larger cases and continue to mine patches in the newly expanded leaves. Development is completed in June and the case is again firmly attached to a leaf and branch. Here the pupa is formed within the case while it is attached to a leaf.
This pest is usually a mere curiosity though populations can reach large enough numbers to cause noticeable brown patches (from the mines) on the foliage of elms.
Strategy 1: Cultural Control - Hand Picking - On small ornamental weeping elms and small Camperdown elms, hand pick the cases that are attached to the branches in the fall and destroy.
Strategy 2: Chemical Control - Larval Control - Several systemic insecticides are registered for control of leafmining insects. Apply one of these in early spring when the casebearers have moved from the branches to leaves or in late July when new casebearers appear.