Agrilus anxius

Bronze birch borer adult. Photo: Whitney Cranshaw, Colorado State University, Bugwood.
Scientific Name: 
Agrilus anxius
Common Name: 
Bronze Birch Borer
Growing Degree Days (GDD's): 
440–880 GDD's, Base 50F, March 1st Start Date. (Source: Cornell Cooperative Extension)
Host Plant(s) Common Name (Scientific Name): 
Asian white birch (Betula populifolia 'Whitespire') *Moderately susceptible.
Balsam poplar (Populus balsamifera) (Paiero et al, 2012)
Bigtooth aspen (Populus grandidentata) (Paiero et al, 2012)
Birch (Betula spp.)
Black cottonwood (Populus trichocarpa) (Paiero et al, 2012)
Downy birch (Betula pubescens) (Paiero et al, 2012)
Eastern cottonwood (Populus deltoides) (Paiero et al, 2012)
European white birch (Betula pendula) *Preferred host. Cultivars may also be attacked.
Gray birch (Betula populifolia) (Paiero et al, 2012)
Himalayan birch (Betula jacquemontii) *Preferred host.
Manchurian birch (Betula platyphylla) (Paiero et al, 2012)
Paper birch (Betula papyrifera) (Paiero et al, 2012)
Quaking aspen (Populus tremuloides) (Paiero et al, 2012)
Sweet birch (Betula lenta) (Paiero et al, 2012)
Water birch (Betula occidentalis) (Paiero et al, 2012)
Yellow birch (Betula alleghaniensis) (Paiero et al, 2012)
Insect Description: 

This is a jewel beetle or flatheaded borer native to North America. It is found throughout the native ranch of birch in Canada and the United States. It will overwinter as a larva, usually 4th instar, but sometimes in different stages of larval development. In the spring, larvae begin to feed again and pupate near the surface. Adults exit the tree, leaving behind a D-shaped exit hole approximately early-mid of June. Mating and egg laying will occur and eggs are laid singly or in groups in cracks and crevices of the host plant bark. Eggs hatch and bore into the bark, starting to feed in serpentine (S-shaped) galleries beneath the bark, between the xylem and phloem. Two years are thought to be required to complete the life cycle. Larvae are the most destructive stage and the feeding galleries they create can effectively girdle trunks or branches. They are cream-colored, dorso-ventrally flattened, with a head slightly wider than their body and a pair of brown, pincher-like appendages at the rear.

Damage to Host: 

This insect can, at times, be a serious pest of forest and shade trees. Damage (exit holes and galleries) may be noticed most on the bark of uppermost branches and bark of trunk and main stem, especially on white and European birch. Canopy dieback, epicormic shoots, and symptoms similar to drought stress may also be caused by feeding of this insect. Bronze birch borer is not thought to be able to complete its life cycle in healthy host plants. Therefore, trees growing under stressful conditions (biotic and abiotic) are more likely to be attacked by this insect.

Monitoring: 

Monitor trees with sparse foliage and chlorotic leaves for bleeding areas of the trunk, swollen S-shaped galleries beneath the bark, twig dieback, and D-shaped exit holes from emerging adults.

Cultural Management: 

Maintaining and/or improving tree vigor is essential for preventing damage from this pest. Avoid pruning birches until late summer (mid-September). Managing other biotic stressors of birch may also help. Some birch species are resistant or more tolerant of this insect, such as the darker barked species (ex. Betula maximowicziana, the monarch birch, Betula platyphylla 'Japonica', Asia white birch, and Betula nigra or river birch) (Johnson and Lyon, 1991). Betula nigra 'Heritage' is noted as a resistant, lighter barked river birch (Davidson and Raupp, 2014).

Natural Enemies & Biological Control: 

Woodpeckers and parasites, including some Hymenopterans like Phasganophora sulcata, are significant predators/natural enemies of bronze birch borers in forested settings. These organisms do not usually provide sufficient management of this insect on susceptible trees under stress in landscaped settings (Johnson and Lyon, 1991).

Chemical Management: 

Acephate (NL)

Azadirachtin (NL)

Bifenthrin (NL)

Chlorpyrifos (N)

Cyantraniliprole (NL)

Dinotefuran (NL)

Emamectin benzoate (L)

Flonicamid+cyclaniliprole (N)

Imidacloprid (L)

Neem oil (NL)

Permethrin (L)

Pyrethrins (L)

Spinosad (NL)

Zeta-cypermethrin (L)

Notes: 

Multiple applications of contact insecticides, according to label instructions, may be necessary to protect vulnerable hosts.

Active ingredients that may be applied systemically include: acephate (injection), emamectin benzoate (injection), imidacloprid (soil drench), and neem oil (soil drench).

When used in nurseries, chlorpyrifos is for quarantine use only.

Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.

Note: Beginning July 1, 2022 neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: January 2024. To check current product registrations in Massachusetts, please visit: https://www.mass.gov/pesticide-product-registration .