Pest profile

Twolined Chestnut Borer

Agrilus bilineatus · Coleoptera: Buprestidae[2]

The twolined chestnut borer attacks stressed oaks; dieback starting at the top of the canopy is the classic sign.[1]

Twolined chestnut borer, a slender bluish-black beetle with two thin pale stripes down its back, on a white surface
Twolined chestnut borer, a slender bluish-black beetle with two thin pale stripes down its back, on a white surface. (c) Douglas Hooper, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Adults are slender, 1/4 to 1/2 inch, bluish-black with two parallel yellow stripes down the wing covers.[1]
  • Larvae are pale, flattened, up to 1 inch, with two pincer-like tails.[1]
  • Infested trees die back from the top of the canopy, and raised ridges appear on trunks and branches.[1]

Look-alikes

Look-alikeHow to tell them apart
Bronze birch borerA related metallic borer of birch, bronze rather than striped.[1]

Where it lives

It attacks native and introduced oaks, white and red, that are stressed and declining.[1]

US map: public records from 33 states since 1990 (GBIF).

Biology and life cycle

Larvae overwinter under bark and pupate in spring; adults emerge in early June in Minnesota and live two to five weeks.[1]

Larvae feed in the phloem, packing galleries with frass; most finish in one year, some take two.[1]

Damage and signs

  • Stress from drought, defoliation, poor sites, root injury or construction makes oaks vulnerable.[1]

Health risk

It attacks trees only; Minnesota Extension mentions no risk to people.[1]

Control

Prevention

Keep oaks healthy and avoid root and trunk injury; stressed trees attract these native borers.[1]

When to call a professional

Insecticides can help protect valued trees.[1]

Common questions

Why is my oak dying from the top down?
Twolined chestnut borer attack on a stressed oak typically starts dieback at the top of the canopy.[1]
Does it attack healthy oaks?
It prefers stressed, declining trees.[1]

Sources

  1. University of Minnesota Extension, “Metallic wood-boring beetles (Yard and garden insects).” extension.umn.edu/garden-and-home/yard-and-garden/yard-and-garden-insects/metallic-wood-boring-beetles (accessed 2026-10-06)
  2. iNaturalist, “Agrilus bilineatus taxon page (order and family).” www.inaturalist.org/taxa/494812 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.