European Elm Flea Weevil (Orchestes alni)
Tagged as: Orchestes alni
The European elm flea weevil 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 reddishbrown 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.
Leaves showing damage from the adults (holes in leaves) and the larvae (blotch-type mines)
The weevil especially likes Siberian elms (Ulmus pumila) and elm hybrids with Siberian elm parentage such as ‘Homestead’.
Keep trees healthy by mulching them properly and watering them during dry periods.
Chemical controls are difficult to apply on a large tree, but when practical, control the flea weevil adults in early May or late June with a spray of acephate, imidacloprid, bifenthrin, or carbaryl. The acephate or imidacloprid will also prevent the larval mines from appearing later.
A systemic soil drench of imidacloprid (Bayer Advanced Insect Control) applied in fall after leaf drop will control early spring feeding of adult elm flea weevils.
A systemic soil drench of imidacloprid applied in early spring will help with the leafminer stage in late spring and the adults feeding later in the season. This drench does not help with the over-wintering adult feeding early in the season as it takes about two months for the insecticide to be taken up throughout the tree.
Refer to the Illinois Urban Pest Management Handbook (University of Illinois Cooperative Extension Service) 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.