With a very large host range, European shot hole borer (Anisandrus [Xyleborus] dispar; also pear blight beetle) stands to do some widespread damage if not managed properly. Recently spotted on Styrax in various sites in Oregon’s Willamette Valley, the pest overwinters as adults in trees and shrubs, including Acer, Aesculus, Alnus, Betula, Castanea, Celtis, Crataegus, Corylus, Cydonia, Fagus, Fraxinus, Juglans, Liriodendron, Magnolia, Malus, Platanus, Populus, Prunus, Punica, Pyrus, Quercus, Salix, Styrax, Tilia, Ulmus and Vitus—with some reports of infestation in Cedrus, Pinus and Tsuga. (Whew, that’s a mouthful.)

According to Robin Rosetta, Associate Professor and Extension Entomologist in the Oregon State University Department of Horticulture, and administrator of OSU’s Pacific Northwest Nursery IPM website (http://oregonstate.edu/dept/nurspest/index.htm), European shot hole borer is among the most common borers in nursery stock, and this is a good time of year to be on the watch for it. Telltale signs are small, round holes that may be weeping sap. Fresh sawdust may appear on the trunk, which would indicate that adults have recently moved in or moved out. And it’s not all that unusual to see the insect’s rear end rather indiscreetly extending from the hole it has bored.

The diminutive European shot hole borer.

Photo courtesy of Kirin Elliott

Adults overwinter in trees they’ve selected, and as the weather begins to turn warmer, the female may emerge to seek another host. An infestation (indicated by holes—and there may be a lot of them) usually signals that the affected plant is stressed, and females are drawn to stressed plants by the ethanol they emit. These borers fly on sunny days when temperatures reach 50 degrees; male borers, which are much smaller than the females, are flightless.

Read more: Infectious Tree Diseases

Monitoring can be aided with a funnel trap, and it’s a good idea to check any trees that may have experienced stress. A heavy infestation can kill a small tree; if enough tunnels are cut into the stem, circulation can be interrupted and the stem weakened.

Male and female adult European shot hole borers; the larger female is seen at the bottom of the image.

Photo courtesy of Robin Rosetta

The best management is … best management: Optimal growing conditions that contribute to optimal, healthy growth may prevent the kind of stress that attracts European shot hole borer.

Read more: Host range matters


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