Bronze birch 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. Bronze birch borer (Agrilus anxius) is a beetle native to North America, so none of the sources below lists it as a pest that must be reported in North America. 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 anxius Gory and the French name agrile du bouleau. NRCan places it among the metallic wood-boring or jewel beetles, and says its larvae give the group the common name flat-headed borers, because of an enlarged segment behind the head.

What the sources say to look for

The NRCan bronze birch borer fact sheet (revision 2024) says adults are slender, olive to copper bronze beetles of 6 to 12 millimetres and are seldom seen. It says sap flow may show on the trunk where larvae enter, that the meandering galleries cut by larvae make criss-crossing welts on the outer bark of large branches and the stem, that adults leave D-shaped exit holes sometimes with coarse sawdust nearby, and that foliage discolouration and early leaf drop begin in the upper crown, followed by branch dieback.

The Oregon State University Extension homeowner guide EM 9189 (revised July 2023) says wilted leaves near the top are often the first sign, and lists rumpled or wrinkled bark, branch dieback and the D-shaped hole. It says that some of these signs can result from other tree health issues, and that the D-shaped hole is a certain indicator of beetles in the family. The Morton Arboretum bronze birch borer page names yellowing and thinning in the upper crown as an early warning sign, with a raised or bumpy bark surface where tunnels run.

Hosts

NRCan says the insect specialises on birch and attacks all native birches in temperate and boreal North America, especially older or stressed trees, with introduced species such as European white birch appearing highly susceptible. The Morton Arboretum sorts birch species into groups. It lists Himalayan birch, European white birch and moor birch as highly susceptible, yellow, sweet, paper and gray birch as showing some resistance, and river birch as highly resistant and rarely affected. NC State Extension says the insect attacks all species of birch, that river birch has low susceptibility in North Carolina, and that it also infests beech.

Life cycle as the sources state it

NRCan says there is one generation a year in southern parts of the range and two years are needed in cooler regions or in vigorous trees. Adults emerge over about six weeks from May to July, eggs are laid in bark crevices, larvae feed under the bark and pupate in cells just under it. The Morton Arboretum gives one generation a year and says eggs are laid in late May or June. Oregon State says larval development takes 1 to 2 years depending on climate and growing season length.

Where it is reported

NRCan describes it as native throughout temperate and boreal North America where birch grows. Oregon State reports it was first detected in Oregon in 2003, in Portland, and in Klamath Falls in 2017, and describes a 2022 driving survey of 312 birch trees there. The sources read give no national count of locations, so none is given here.

Regulated status

None of the North American pages read lists it as regulated. NRCan says its attack on European birches in North America led the European Union to declare it a quarantine pest, and that imports of birch wood products into the Union, including wood packing, need bark and outer sapwood removed or treatment under a national plant protection organization's supervision. No European Union order page was read for this profile. For what the agencies in each country ask people to report, see the guides on Canada and the United States.

What the sources say about moving wood

Oregon State says transport of firewood is one way the insect moves to new places, and suggests locally sourced firewood. NRCan lists chipping, burning or exposing infested material to full sunlight among sanitation measures. See also the guide on moving wood and firewood.

Management as the sources list it

NRCan calls the insect a secondary pest of old and weakened trees, and its management section lists mulching and watering, sanitation of infested material, natural enemies and insecticides, with a pointer to Health Canada's pesticide database. Oregon State and NC State both describe watering and avoiding pruning during the adult flight, and Oregon State notes that tree injection products are available only to professional applicators. The Morton Arboretum points readers to its Plant Clinic for current insecticide recommendations. This page gives no product names, rates or timings. For who may apply, see pesticide licences.