Be On the Watch for This Elm Insect
Jeffrey Hahn, Asst. Extension Entomologist
The European elm flea weevil (EEFW), Orchestes alni and it's damage, was found on the University of Minnesota St. Paul campus during July. It was found by Dr. Curtis Young, an extension entomologist at Ohio State University. This invasive insect, common throughout Europe, was first found in the U.S. in 1982. It wasn't found in the Midwest until 2003. It was first found in Minnesota in 2007 when an adult was collected on the St. Paul campus.
The adult EEFW is small, 1/10 - 1/8 inch long. It is reddish brown with black spots or dark brown to black, with a long, conspicuous snout and large back legs which allows it to jump. This weevil feeds on Siberian elm, Chinese elm, and hybrids with Asian parentage. It rarely feeds on American elm.
EEFW overwinters as an adult and becomes active in the spring. It moves to elm and feeds on the underside, windowpaning small areas, i.e. feeding on the lower surface of leaves but not chewing through. A thin, opaque layer of leaf tissue remains. Eventually, this chewed area dries up and fall out. Don't confuse this injury with elm leaf beetle feeding which chews small oval holes in the leaves with the edge of the holes remaining green.
Soon after they emerge and feed, adults lay eggs along the edges of the veins. When the larvae hatch, they feed as leafminers inside the leaves. They move to the tip of the leaves where they create blotch mines. The larvae feed for a few weeks and then pupate. Adults emerge later in the summer and feed until fall.
The feeding damage by EEFW is primarily cosmetic, only affecting the appearance of the tree. It is very unlikely that elm are injured as a result of EEFW feeding making treatment unnecessary. It is possible that if trees were severely defoliated, particularly if they are recent transplants or already stressed, they could further weakened elm and make them more susceptible to other problems. If treatment is desired, an application of imidacloprid in early spring should be sufficient to manage this weevil.
We are interested in sightings of this insect and/or its damage in other areas of Minnesota. If you believe you have EEFW, please contact Jeff Hahn (firstname.lastname@example.org ).