Bronze Birch Borer

Bronze Birch Borer (Agrilus anxius) is a native, metallic wood-boring beetle that attacks Birch trees.

Bronze Birch Borer larva

Bronze Birch Borer Life Cycle

Related to both Two-Lined Chestnut Borer and the Emerald Ash Borer (invasive), Bronze Birch Borer causes its damage to trees during the larval stage. The larva feed on conductive sapwood and cause restriction of “sap flow” to the above branches, and girdling/dieback of the branch follows. Larval overwinter under the bark, and emerge in May or June of the following year.

Adult beetles feed and mate, prior to laying eggs on the bark surface of branches. Eggs take a couple of weeks to hatch, before new larva burrow into the tree’s sapwood layer; and the life cycle continues.  Adult beetles are an iridescent, bronze color, and ~1/4-1/2” in size. The larva are cream colored, flat grubs with 2 protrusions near their tail end, and measure ~1” when mature.

Signs & Symptoms of Bronze Birch Borer

Bronze Birch Borer damage

Non-native Birch cultivars and native stressed Birch trees tend to be the first infested by Bronze Birch Borer. While River Birch can (and is) infested by BBB, it does not seem to be a preferred target. BBB-resistant tree cultivars are commonly cross breed susceptible White Birches, with the more resistant River Birch.

Symptoms and signs of a Bronze Birch Borer infestation include:

  • D-shaped exit holes (left behind when adults emerge)

  • callusing under the bark (can be seen on the thin-barked Birch)

  • larval galleries under bark of dead/dying branches

  • thinning of the tree’s canopy, and limb dieback

Left untreated, BBB can cause tree mortality over the course of a couple years.  BBB can also be indicative of other tree stressors (construction damage, flooding, drought, other insect or disease, etc.), and it is important to address all site factors when devising a treatment plan.

Treating Bronze Birch Borer

Treatments for Bronze Birch Borer have high-efficacy rates, if implemented in a timely manner.  Trees are likely to recover after treatment, especially if other site factors are also addressed.  Innovative Tree Care offers systemic insecticide injections and soil applied products, which offer both preventative and therapeutic protection. 

If you suspect a Bronze Birch Borer infestation, or notice other decline in your Birch tree, contact us (click below) for a proper tree assessment/inspection and treatment plan (if warranted).