Bronze Birch Borer

Agrilus anxius

Crops Affected: Various species of birch

Life Cycle:

• Adults are metallic olive to bronze-coloured, slender-bodied beetles that are 0.25-0.5 inches long
  • Males are generally somewhat smaller than females
• Adults are active and feed from June to August in the Prairies
• Adults can fly long distances to find hosts
• Females lay clusters of eggs in crevices and cracks in the bark of host trees
  • Eggs are oval, flattened and whitish, turning yellow over time
• Larvae have slender, white, legless, flattened, segmented bodies, with a light brown head
  • Larvae also have two brown, pincer-like tails at the end of their abdomen
  • Larvae can be over one inch long when mature
• Larvae emerge and mine/bore in the cambium (growth/expansion tissues) and phloem tissues,
  creating criss-crossing galleries
  • Larvae later bore into the sapwood of the tree to overwinter
  • Most larval feeding is in the main stem and upper branches of the tree
• Older larvae pupate in spring under the bark in oblong cells

• Adults emerge by chewing through the bark
• The life cycle can be 1-2 years, depending on the location

Symptoms / Damage:

• Generally already weakened, larger, older trees are attacked
• Larval boring in the growth tissues results in the eventual girdling
  of larger branches and the main trunk, restricting the movement of water and nutrients
• First signs of infestation are spare yellow leaves in the upper crown of a tree
• Twig and branch dieback spreads through the entire crop, with the tree eventually dying
  • Tree death rates can range from 1 to may years, depending on other stresses
• Larval galleries result in callus (undifferentiated cellular tissues) formation over them, giving swollen ridges
• Emerging adults leave a characteristic D-shaped exit hole

Monitoring:

• Watch for thinning crown and branch dieback
• Closer examination of dying branches
  • Watch for D-shaped exit holes and swollen ridges
    over larval galleries

Management:

• Ensure trees are free from stress – avoid drought, wounding and regular defoliation
  • Ensure trees are well-watered during dry years
• Avoid planting trees in poor locations – birch prefer cool, moist sites and shaded soils
• Damage by construction, mowing, etc. can also affect tree health
• Injection or soil drenching with a systemic chemical (limited options and many restrictions) has some limited capabilities of helping a tree recover