Issue 7, June 4, 2010

European Elm Flea Weevil

European elm flea weevil, Orchestes alni, is feeding throughout the state. This is a tiny insect, about only 1/16 inch long. It is reddish, with black spots on the wing covers, and has on elongated snout with tiny mouthparts at the end. Adults overwinter, emerging in the spring to feed on leaves of Eurasian elms, including Siberian elm, where the damage is most noticeable. Hybrids of elms bred for Dutch elm disease resistance tend to be heavily attacked, but Morton Accolade and Morton Glossy were lightly attacked in research recently published by the University of Kentucky. It also feeds on American elm, but less so than those from Eurasia.

Adult feeding occurs initially as pinhead-sized, round holes in the foliage. These holes enlarge through additional feeding and/or dieback into larger, more noticeable holes. Many holes are produced, making them the easiest way to detect this weevil's presence. Close examination reveals the tiny weevils on the leaf. When disturbed, they jump and fly, earning them the flea in their name.

Flea weevils mate in the spring. Mated females chew holes partway through the leaf tissue and then turn around and lay an egg in the hole. These hatch into legless, white larvae that mine through the mesophyll leaf tissue at the leaf tips, creating leaf tips that are initially whitish but soon turn brown.

When fully grown, the larvae pupate within the mine and emerge as adults in June. After feeding for several weeks, they seek overwintering sites in protected locations. They emerge in the spring to feed on the new foliage.

Control of both insects is primarily directed against the adults. Sprays of acephate (Orthene), imidacloprid (Merit), bifenthrin (Onyx. Talstar), or carbaryl (Sevin) should provide control. Soil injection of acephate (Lepitech) or imidacloprid should also be effective.--Phil Nixon

Phil Nixon

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