Tea shot hole borer

Euwallacea fornicatus, E. fornicatior, E. perbrevis and E. kuroshio

1. Identification

• Common name: Tea shot hole borer, polyphagous shot hole borer, ambrosia bark beetle complex
• Scientific name: Euwallacea fornicatus Eichhoff, E. fornicatior Eichhoff, E. perbrevis Schedl, E. kuroshio Gomez & Hulcr
• Order: Coleoptera
• Family: Curculionidae (Scolytinae)

2. Description of the pest

• Adults: Small beetles (≈ 2–2.5 mm); dark brown colouring; cylindrical body typical of bark beetles; winged females responsible for colonisation.
• Larvae: Legless, whitish, develop inside the galleries.
• Eggs: Laid inside the galleries excavated in the wood.
• Obligate association with symbiotic fungi (“ambrosia fungi” - these are fungi cultivated by the bark beetles inside the galleries, serving as the exclusive food source for the larvae and playing an essential role in the colonisation of the wood), responsible for the degradation of the plant tissue and for feeding the larvae.

3. Main hosts

• Tea.
• Avocado.
• Various ornamental and forest woody species (e.g.: Acer spp., Salix spp., Platanus spp., Quercus spp., Cercis spp., Persea spp., Camellia spp.).
• Highly polyphagous species, with hundreds of recorded hosts.

4. Symptoms and damage

• Perforations in the trunk and branches, with the expulsion of fine sawdust (sawdust “threads” or “toothpicks”).
• Internal galleries that compromise sap transport.
• Wilting, yellowing and death of branches.
• Progressive decline of the tree in severe attacks.
• Damage mostly associated with the symbiotic fungus, which causes vascular necrosis.

5. Biological cycle

• Adult females carry the symbiotic fungi in specialised structures (mycangia).
• Colonisation begins with the perforation of the trunk or branches.
• Eggs laid in the galleries; larvae feed on the fungus cultivated inside.
• Continuous development throughout the year in warm climates.
• Predominance of females; males rare and wingless.
• Several generations per year.

6. Monitoring

• Observation of recent perforations and expulsion of sawdust.
• Identification of symptoms of sudden decline in branches.
• Traps with ethanol or other volatile attractants for the detection of adults.
• Assessment of susceptible host trees in parks, orchards and nurseries.

7. Management measures

• Cultural: Removal and destruction of infested branches and trunks; elimination of dead wood; avoid water stress in plants.
• Biological: Conservation of local natural enemies (predators and parasitoids of bark beetles).
• Integrated protection: Regular monitoring; avoid transport of infested wood; application of phytosanitary measures in nurseries; chemical treatments with limited efficacy due to the cryptic habit of the pest.

Bibliographic references

• EPPO Global Database – Euwallacea fornicatus complex.
• CABI Invasive Species Compendium – Euwallacea fornicatus complex.
• Hulcr, J. & Stelinski, L. (2017). The ambrosia beetle–fungus symbiosis.
• Eskalen, A. et al. (2013). Host range and impact of Euwallacea spp. in woody plants.