The European elm flea weevil (Orchestes alni) has been a pest on elms in the upper Midwest only since 2003, though it was first discovered in the U.S. in 1982. It is especially common on Siberian elms. The insects are tiny weevils about 1/16th of an inch long with long snouts. They are reddish brown with black heads and have black spots on their wing covers. Their hind legs are thickened and useful for jumping. They fly when disturbed.
Adults begin chewing small holes in young leaves in May and early June, usually from the underside of the leaf. Heavy feeding may cause young leaves to turn brown and fall off. The females lay eggs in the mid-vein of the leaf. The larvae hatch soon after and begin to mine the leaf-tip. Eventually the mine enlarges to become a blotch. The larvae pupate within the leaf, emerging as adults in late July or early August. The adults overwinter under loose bark and in leaf litter under infested trees.
The adults eat small pin-head sized holes in leaves, while the larval stage cause blotch-type mines at leaf tips. The damage from European elm flea weevil is considered more an aesthetic problem and will not kill the tree. However, extensive feeding can cause severe defoliation which can weaken the tree, making it more vulnerable to other insect or disease problems.
The weevil feeds on elms especially Siberian elms (Ulmus pumila) and elm hybrids with Asian parentage.
Keep trees healthy by mulching them properly and watering them during dry periods.
Pesticides are difficult to apply on a large tree, but when practical, control the flea weevil adults in early May and late June with a spray of acephate, imidacloprid, or carbaryl. The acephate or imidacloprid will also prevent the larval mines from appearing later.
Refer to University of Illinois Extension publication "Pest Management for the Home Landscape" for a complete listing of chemical recommendations. Use pesticides safely and wisely; read and follow label directions. The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.
From Morton Arboretum Website: