Twolined chestnut borer: what the agencies record

This page describes what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. The twolined chestnut borer (Agrilus bilineatus) is native to North America, and none of the pages read lists it as regulated or notifiable. Each section names its source, all read on October 8, 2026. The parent page, insect pests of trees, compares it with the other pests on the list.

Names

Natural Resources Canada, called NRCan, gives the scientific name Agrilus bilineatus (Weber), the French name agrile du chataignier and the alternative spelling two-lined chestnut borer. It places the beetle in the family Buprestidae. NC State Extension calls that family jewel beetles, also called metallic wood-boring beetles, and says the twolined chestnut borer is in the same family as the emerald ash borer. The Minnesota Department of Natural Resources, called Minnesota DNR, writes the name as twolined chestnut borer.

Hosts

NRCan says the beetle attacks several species of oak and American chestnut. In Canada it says the beetle is most often found on weakened red oak, white oak and bur oak, and that oaks in the red oak group are more susceptible than those in the white oak group. NC State says it attacks oaks in both the red oak and white oak groups, and names northern red oak and scarlet oak in the red group and white oak and chestnut oak in the white group as common North Carolina hosts. Both pages say American chestnut is relatively rare, or was decimated, because of chestnut blight. NRCan adds that discoveries of the beetle in Turkey in 2018 raise concerns about European chestnut and oak, and that English oak is known to be highly susceptible.

Where it is reported

NRCan says the insect is native to North America east of the 100th meridian, from Manitoba to New Brunswick in Canada and in the eastern United States wherever its hosts grow. NC State describes it as native to eastern North America, including North Carolina. Minnesota DNR shows symptoms of the borer after years of drought stress in Dakota County, Minnesota, in 2023.

What the sources say to look for

NRCan describes adults as elongate beetles 4 to 13 millimetres long, dark with two golden stripes along the back. NC State gives a size of 0.2 to 0.5 inches, metallic black with a bluish iridescence and a pale golden stripe on each wing cover. Larvae are cream-white and elongated, up to 25 millimetres long by NRCan and about 1 inch by NC State, with a flattened head. NC State adds a pair of spines at the tip of the last body segment.

The larvae bore winding galleries under the bark, and NRCan says the tunnels are filled with sawdust and frass. Adults leave D-shaped exit holes, which NRCan puts at 5 millimetres. NRCan says the first symptom of established galleries is wilted foliage on scattered branches in late summer, and that branch death starts in the upper canopy and moves lower. NC State describes wilted, brown foliage in late summer followed by branch dieback, beginning near the top of the tree. Minnesota DNR says the first sign is often subtle dieback at the edge of the canopy, and that the more drastic dieback is often first seen from mid-July to mid-August.

NC State warns that the D-shaped hole looks like that of the emerald ash borer, and says the host plant is the way to separate the two: that borer attacks only ash and white fringetree. Minnesota DNR says exit holes and galleries do not necessarily mean the twolined chestnut borer killed the tree, because oaks that die from oak wilt or Armillaria root disease can be attacked afterwards. On red oaks, it says dead leaves that stay on the branches for months set borer attack and Armillaria apart from oak wilt, while white and bur oaks can look nearly identical to oak wilt and experienced pathologists rely on a laboratory result. For that disease see the oak wilt page.

A secondary pest, as the sources put it

All three sources call the beetle a secondary pest. NRCan says it only successfully attacks trees under stress from drought or earlier defoliation by leaf-feeding insects. NC State lists water and nutrient shortage and defoliation, and ties the borer to oak decline, a complex in which no single stress agent dominates. Minnesota DNR names old age, crowding, severe drought and defoliation, and says it takes three things to confirm a decline: the factors that made the stand susceptible, the trigger such as drought, and the insect or disease that finishes the tree. NRCan says trees usually die after 2 to 3 years of attack and can be killed in the first year if already compromised. Minnesota DNR says declines can stop, and that a tree can persist with a dead top for many years. The wider group of pests and diseases is on the tree pests and diseases page.

Life cycle as the sources state it

NRCan says there is usually one generation a year, sometimes stretched to two in vigorous hosts or cooler climates. The beetle overwinters as a final-stage larva in a chamber under the bark and pupates there in spring. Adult emergence peaks from June to July, and adults feed on leaves while they mature. Mated females find stressed trees through chemicals the trees give off and lay eggs in bark crevices. NC State agrees on one generation a year, with larvae feeding during the growing season and adults emerging in spring or early summer.

Regulated status and reporting

None of the three pages names a regulation, quarantine order or report line for this beetle, which NRCan calls a natural component of oak and chestnut forests in eastern North America. For the agencies that take reports of regulated pests, see the guides on reporting a pest in Canada and the United States.

Moving wood

NRCan says wood with bark moved to new areas could hold fully grown larvae ready to emerge. Wider rules on firewood are on the moving wood and firewood page.

Management as the sources list it

NRCan says larvae under the bark are out of reach of most treatments short of removing the tree, and that management leans on prevention. It lists thinning overstocked stands, avoiding new root disturbance and soil compaction, and mulching, watering and fertilizing urban trees. For single high-value trees it lists pruning below the last wilted leaves in the first year of an infestation, and says removal with destruction of the bark is the only option listed once a tree has been infested for a second and third year. NC State lists watering, mulching, planting oaks suited to the site, avoiding wounds to trunk and roots, and managing leaf-feeding insects. Minnesota DNR lists mulch and watering for yard oaks and says removing declining trees cannot eradicate the beetle from a stand, that outbreaks decline on their own, and that trunk injections and other treatments for valuable oaks are for a professional arborist to assess. This page gives no product names, rates or timings. For who may apply pesticides, see pesticide licences.