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Ambrosia Beetles

Ambrosia Beetles (Curculionidae: Scolytinae)

Ambrosia beetles are wood-boring insects that belong to the bark beetle subfamily. Unlike other bark beetles or wood-borers that feed on the inner bark or wood tissues, ambrosia beetles bore directly into the xylem to construct gallery tunnels where they then cultivate symbiont “ambrosia” fungi. The beetles and their larvae feed on this fungi rather than the wood itself.

The fungal inoculation process that these beetles use often introduces pathogens into the tree’s vascular system (such as Raffaelea or Fusarium fungal species), that lead to wilting, dieback, and tree mortality. Many ambrosia species are attracted to ethanol that is emitted by stressed, flood-damaged, or freeze-injured landscape trees or nursery stock.

Quarantine and Management Policies
  • Interstate movement of infested nursery stock, timber, and untreated firewood is strictly regulated.
  • Movement of all Lauraceae host plants (Sassafras, Spicebush, Redbay, Avocado) out of infested regions is restricted under federal and state agricultural quarantines due to the danger of Xyleborus glabratus and Raffaelea lauricola infections.
  • Commercial nursery stock shipped interstate must come from certified pest-free facilities inspected by state Departments of Agriculture (e.g., NJDA, USDA-APHIS).
    • Infested blocks must be immediately quarantined.
  • Destroy trees exhibiting active toothpick frass or gallery wood-staining. They cannot be saved with insecticides and can encourage further infestations.
  • If chipping infested woody material, process the pieces smaller than 1 in x 1 in to kill any surviving larvae and adults inside the wood. Spray woodchips with a contact insecticide when chipping during peak flight periods.
Diagnostic and Scouting Guidelines
  1. Monitor Emergence:
    • Spring emergence begins rapidly when maximum daily temperatures consistently exceed 68-70F (100-250 GDD). Monitor forecasts closely during early spring leaf-out.
    • Hang funnel traps, clear sticky panels, or home-made soda bottle traps baited with 70-95% ethanol.
      • Position traps 2-3 off the ground along wooded field edges, brush lines, and nursery blocks. Check traps weekly starting in early March to pinpoint exact flight timing.
    • Focus scouting on the lower 2-3 feet of the tree trunks, graft unions, and major scaffold branches.
    • Look for thin frass “toothpicks,” or 1-2 cm long cylinders of packed sawdust extending out from stem entry holes.
      • Rain or overhead irrigation can wash these away, leaving only 1mm circular holes.
    • Look for weeping sap, water-soaked bark staining, or localized cambial dieback that surrounds the entry pinholes.
    • Cut into affected stems to look for brownish-black fungal staining around the larval galleries in the xylem.
  2. Identify Weak Plants and Risk:
    • Protective scouting and early identification is crucial for detection and management of ambrosia beetles because systemic insecticides are ineffective after the beetles enter the wood.
    • Take special care of plants to avoid plant stress. Pay close attention to plants when they are stressed, flooded, frost-injured, or root-bound, as these plants produce ethanol aerosols that attract colonizing female beetles.
  3. Submit Samples