Exotic Elm Tree Pest Found for First Time in Ohio

June 28, 2007

COLUMBUS, Ohio -- An exotic insect that can cause cosmetic damage to elm trees has been reported for the first time in Ohio.


The European elm flea weevil (Orchestes alni), first found and identified in the Midwest in Illinois and Wisconsin in 2003, was recently discovered feeding on Siberian elms (Ulmus pumila) in northwest Ohio by Ohio State University Extension entomologist Curtis Young. Young initially suspected the feeding damage was caused by a more common insect, the elm leaf beetle -- until he inspected the damaged trees a bit more closely and discovered the true culprit.

"I could find no adults or larvae at the defoliation site or on the ground, indicative of elm leaf beetle presence. I then took a closer look at the leaves and found a large number of small brown beetles that jumped like flea beetles when disturbed," said Young. "When I examined them under a hand lens, I found that the beetles had a proboscis, or long snout, suggesting that they were weevils. The insect was soon identified as the European elm flea weevil."

The European elm flea weevil, common throughout Europe, was first identified in the northeastern U.S. in 1982.The tiny adult is black or dark brown with a prominent proboscis and a distinctive enlarged femur on the hind leg that identifies it as a flea weevil. Adults appear in the spring and feed on the underside of newly emerging leaves. After feeding, they lay eggs along the leaf veins. The larvae, acting as leaf miners, will feed for several more weeks before they pupate. Adults emerge throughout the summer and resume feeding on the host elms until they seek overwintering sites on or near the host plants. Entomologists speculate that the European elm flea weevil only goes through one generation per season.

"Feeding from the European elm flea weevil won't kill an elm tree, but if the feeding is extensive enough to cause severe defoliation, that could potentially weaken the tree and expose it to other stresses," said Young. "The thing that is particularly concerning about the cosmetic damage the insect causes is that it feeds on popular green industry species and those that have few known insect pests. This, of course, can impact the aesthetic value of the tree."

The most common host of the European elm flea weevil is the Siberian elm, which is a common landscape and street tree. Other hosts are elm hybrids, such as ‘Homestead' (a hybrid involving three elm species -- U. carpinifolia, U. hollandica and U. pumila), that has been produced specifically for Dutch elm disease resistance. The true Chinese elm (U. parvifolia) is also a suitable host, a popular elm because of its unique appearance and because it has very few known insect pests.

Young said that steps can be taken to identify, control and manage any defoliation damage to elm species:

• Identify the source of the defoliation, especially if the damage is caused by an insect. Elm species are host to a variety of insects and pests, such as a sawfly leaf miner, the European elm scale and caterpillars of several butterflies. "For example, identify whether it's elm leaf beetle or elm flea weevil, as the feeding damage caused by both is very similar, and can be confusing," said Young.

• In cases of severe defoliation, adult insects, including the European elm flea weevil, can easily be controlled with foliar insecticides.

• Trees can recover from severe defoliation damage with proper care and maintenance to induce good plant health, such as watering, pruning, fertilizing and mulching.

If European elm flea weevil is suspected or identified, landscape and nursery professionals, urban foresters, homeowners, or other individuals are encouraged to contact Young at (419) 222-9946, or young.2@cfaes.osu.edu.


Candace Pollock
Curtis Young