While emerald ash borer (EAB) has certainly made itself known in recent years, there are plenty of other borers affecting Wisconsin trees. In fact, these additional borers have killed many more trees than EAB has. So while you're treating ash trees to prevent EAB, don't forget about some of the other deadly insects.
Bronze Birch Borer
Bronze birch borers are slender, olive-bronze beetles with olive reflections. They prey on birch trees that are already distressed or planted in the wrong areas. These borers live as larvae under the bark in the winter and emerge as adults in the spring, chewing their way through the bark. Their feeding blocks the flow of water and nutrients to the leaves, causing branches to die, starting at the top of the tree.
Linden borers are olive-green beetles with three distinct black spots on each wing. They feed just below the bark on linden and basswood trees, cutting off nutrients to the roots and leaves. Bark will bulge where the insects are feeding and leaves at the top of the tree will be smaller and fewer, and eventually begin to die.
Two-lined Chestnut Borer
Two-lined chestnut borers are slender beetles with two golden lines down their backs. They feed just below the bark on black, white, red and bur oaks. As adults, they feed on foliage and usually attack trees weakened by droughts or storm damage. Leaves will begin browning on top and side branches as the infestation progresses. These borers commonly kill young, recently transplanted trees.
Viburnum borers are wood-boring insects that feed on the lower part of viburnum trunks, branches and roots. They are day-flying moths that look similar to wasps, with bluish-black bodies and yellow markings. Adults emerge in June and July to lay eggs near wound sites, then the larvae tunnel and feed under the bark. Since they usually attack near the base of the tree, swelling and emergence holes may be seen on the lower portion of the trunk.
Beech borers feed on the trunks of sapling red oaks. As adults, they are brownish-gray long-horned beetles. They create vertical slits in the tree's trunk, close to an inch in length, and then pack it with grayish frass that extrudes in ribbons from the hole. The larvae of these insects chew holes in the wood of the tree, creating damage and weakening the tree.
If you’re concerned that borers are harming the trees in your yard, call an arborist!