Poplar Borer

Causal Organism: Saperda calcarata

Crops Affected: poplars, trembling aspens, and willows

Life Cycle:

• Trunk-boring beetle
• Trees are not usually killed by poplar borer, however trunks may be weakened by the tunnelling and may snap in windstorms
• Often find damage and signs of infestation in trees that are growing in the open or on the edges of bluffs
  • Will affect stressed or weakened trees (sunscald, drought, partial cutting, etc.) as well as healthy trees
• Adults are up to 25 mm (1in) long, with antennae of a similar length (i.e. very long antennae)
  • They have grey coloured bodies with faint yellow stripes and small brown spots
  • Adults emerge in late June or July
    • Live approximately 6 weeks
    • Feed on foliage and begin laying eggs within about one week
  • Females cut crescent-shaped holes/notches/punctures in the bark of the tree
    • Deposit 1-2 creamy white eggs within the notch
    • Eggs tend to be laid in exposed spots on the trunk or lower crown
  • Eggs hatch within approximately 3 weeks
  • Larvae are grub-like, legless, and creamy-white with a brown head and brown thoracic shield (a.k.a. upper back/neck area)
    • Larvae can reach about 40 mm (1.5in) when full-sized
    • First year larvae feed on the inner bark, feeding from the time that they hatch until about October
      • Hibernate in the burrow
    • Second year larvae start feeding in late April, boring through the sapwood into the heart of the tree
      • Overwinter in a cell of tightly packed frass (a.k.a. poop) within the burrow
    • Second and third year larvae will eject the sawdust from their burrow
      • Observed outside their burrow
      • Sign of infestation
    • Third year larvae start feeding in April (like second year)
      • Stop feeding in August to build a pupation cell
      • Overwinter as a pre-pupa
    • In May of the fourth year, pupation starts, and the adults will emerge that summer
      • Full cycle complete
    • Infested trees are often attacked repeatedly
      • As the next generation emerges, it tends to lay its eggs on the same trees
      • Form “brood trees”

Symptoms:

• Infested trees often exude copious amounts of a varnish-like sap that runs down the surface of the trunk, staining the bark
  • Very distinctive symptom of infestation by this pest
• Exuded sawdust by the burrowing larvae is another characteristic symptom of this pest
• Woodpeckers may be observed feeding on trees
  • Causes more damage, but may reduce the population of the pest (good/bad)
• The open holes that the larvae maintain to expel sawdust can become infected and harbour a rot fungus that damages the tree further

Management:

• Limited management options
• Can try and kill the larvae mechanically, using a fine wire that is threaded up into the burrows
  • The larvae can be as much as 25 cm (10in) deep
  • Can be challenging to reach them
• Apply insecticides to control active adults, preventing egg laying
  • May get some contact with shallow larvae, but not likely
• Encourage healthy trees and growth, as this will help to resist attacks
• Heavily infested trees should be removed
  • Reduces risk of damage from falling trees
  • May reduce populations slightly

Dark, varnish-like sap is exuded from holes, staining the trunk

Photos by: Robert Spencer