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Longhorn beetle

The longhorn beetle is not associated with tree death, but larvae mine in trees already damaged by fire, drought, or recently felled for firewood.

A longhorn beetle found on the fairgrounds last weekend, probably attracted from some nearby wooded area to bright evening lights, prompted a lengthy discussion of beetles in the 4-H goat barn. Male longhorn beetles, members of the family Cerambycidae, are easily recognizable due to ultra-long antennae. Differences in antennae are often used to distinguish male and female insects: an impressive moth found by another 4-H participant was clearly female because it did not have the feathery, plumose antennae common to male moths, used to locate mating partners.

As summer progresses into warmer, drier weather, signs of wood-boring beetles like the Cerambycidae become more obvious in our trees. Consider monitoring your trees for these pests if your property includes the tree species affected by the five wood boring beetles described below.

Bronze birch borer: This Buprestid beetle is a member of the genus Agrilus, beetles that look similar, but are different in that they each attack one or just a few species of trees. Bronze birch borer (BBB) attacks only birch, while a closely related species attacks only poplar. BBB, first confirmed in Klamath Falls just a few years ago, is now common in landscape birches that are poorly irrigated. Like most of the beetles considered here, BBB is attracted to trees that are stressed or wounded. Unlike many of the other beetles, BBB leads to the quick death of birches: other beetles may develop within the tree for many years without killing it.

Flatheaded cedar borer: Like BBB and most Buprestids, flathead cedar borer adults appear to be metallic or shiny. This pest can be problematic in tree nurseries, killing young trees in production, but is less common in established landscapes. In nurseries, infestations are almost always associated with pruning cuts, drought, weedeater wounds, or other tree injury. This beetle probably does not kill mature trees in well-irrigated landscapes.

Cedar bark beetle: The Scolytid beetles are another huge wood-boring beetle group, commonly referred to as bark beetles. There are numerous Scolytid species: generalists feeding on a wide range of trees, and others like the cedar bark beetle feed only on one type of tree — in this case, true cedars. One of the first signs of this, and any wood boring beetles, is single branches and twigs dying- first one, then scattered throughout the tree. This is due to the egg-laying and feeding patterns of these insects. Adults feed little, but the larvae feed in the cambium, where all the tree’s feeding and nutrient exchange is taking place. Bark beetles are very small — usually less than 1/8 inch — and build up huge aggregations. When the adults emerge from a tree, they leave many tiny little holes in the bark, resembling “shot holes.” This is one of the signs to look for when monitoring trees. In spring and during active growth, the shotholes often drip sap.

Oregon fir sawyer: This longhorn beetle feeds on more than firs: hosts also include pines and spruces. Adults are shiny black and around an inch long, with a distinct white spot at the base of the wings. This beetle is not associated with tree death, but larvae mine in trees already damaged by fire, drought, or recently felled for firewood. In the latter case, the sawyer can cause damage to the harvested wood. To find evidence of any wood boring beetle feeding, the bark is peeled away to reveal larval “galleries” — the tunnels the larvae create as they feed. The size and pattern of galleries is used to help identify the species of beetle involved in infestation.

Ponderosa pine bark borer: Grey and black stripes on the body and antennae of this 1/2-inch long beetle give it a dramatic and striking appearance of being capable of serious damage, but they are most commonly found on trees already attacked by western pine beetle, one of the tiny Scolytids. As such, the ponderosa pine bark borer is typically considered a secondary pest. The ponderus borer, a rather plain solid-brown relative, is responsible for far more tree mortality.

In cases of prolonged and extreme drought, any wood boring beetle might cause tree mortality, but this is not always the case. Inspect trees for single dying branches, exit holes from adult insects, and adult beetles attracted to lights at night. It is difficult to detect larvae feeding inside the tree until some damage has already occurred. Tiny Scolytid adults leave numerous tiny holes, while the Buprestids and Cerambycids leave holes from a quarter to half inch wide-round for Cerambycids and “D” shaped for Buprestids. If you have concerns, the Master Gardeners and horticulture faculty at your county extension office can help you identify the wood boring beetles you encounter.

Nicole Sanchez is horticulture faculty at OSU’s Klamath Basin Research and Extension Center. For more information on this or other gardening topics, contact Nicole at Nicole.sanchez@oregonstate.edu or 541-883-7131.