Polyphagous shot-hole borer

Polyphagous shot-hole borer is a wood boring beetle.

Adult

• Females are very small, approximately 2mm in length and range from brown to black in colour.
• Males are smaller at approximately 1.6mm in length.
• Females can fly, males do not fly and are wingless.
• Adult females are the only life stage found outside of the tunnel complex.

Eggs

• Eggs are extremely small (0.3mm), round and partly translucent.
• Can be laid singly or in groups.
• Eggs are pale to begin and darken over time.

Larvae

• Very small, white in colour, legless and 'C' shaped.

Pupae

• White in colour and similar size to adults.

Plant stage and plant parts affected

Polyphagous shot-hole borer typically affects mature plants but can affect saplings with sufficient branch diameter. Trunks, branches and stems greater than 2cm in diameter can be infested.

Plant damage

External symptoms of polyphagous shot-hole borer infestation include water-soaked lesions or staining surrounding small borer holes in the branches or trunks of infested trees. These holes are often surrounded by sap, resin or borer frass (a light coloured powdery substance). In some species the borer holes and damage may only become evident when the bark is removed. Affected trees may show signs of wilting and branch dieback and in severe cases, tree death.

Polyphagous shot-hole borer is similar to closely related species, tea shot-hole borer (Euwallacea perbrevis), which is present in Queensland and New South Wales and Kuroshio shot-hole borer (Euwallacea kuroshio), which is not present in Australia.

Genetic testing by experts is needed to distinguish polyphagous shot-hole borer from tea and Kuroshio shot-hole borers. If you suspect you have found polyphagous shot-hole borer, contact Biosecurity Queensland on 13 25 23 or report it online.

Native to Asia (China, Japan, Thailand, Vietnam), polyphagous shot-hole borer has spread to Israel, South Africa, and the United States of America.

Detected near Perth, Western Australia in August 2021, polyphagous shot-hole borer has not been recorded elsewhere in Australia.

The tea shot-hole borer, a closely related species (previously Euwallacea fornicatus, now Euwallacea perbrevis) is known to be present in Queensland and NSW.

Over 400 plant species in 75 plant families have been recorded to be attacked by polyphagous shot-hole borer, and over 100 species are recorded as reproductive hosts. The cultivation of the fungus food source is essential for polyphagous shot-hole borer survival and breeding therefore reproductive hosts are those plant species that are susceptible to Fusarium infection.

A wide range of plants have been recorded as susceptible to polyphagous shot-hole borer including tree crops (such as avocado and mango) and native forest species. Additionally, the host list may increase after establishment if polyphagous shot-hole borer forms symbiotic relationships with other Fusarium species.

• Mated adult females bore into branches creating a tunnel complex in which to lay eggs.
• Eggs, larvae and pupae remain within the tunnel.
• Eggs hatch after 4–6 days.
• Larvae take 16–18 days to develop, before they enter pupation.
• Adults emerge from pupae after 7–9 days.
• The female adults remain in the tunnel gallery after emergence from pupae and mate with males from the same parent.
• After mating the females leave the tunnel to disperse and they may fly to nearby trees if the existing host is highly infested or becomes too stressed. The adult males are flightless and remain in the tunnel for life.
• Female flight dispersal is typically short range, less than 40m, although longer distances have been observed if environmental conditions are conducive (i.e. wind).

Polyphagous shot-hole borer infests a very wide range of host plant species and, unusually for borers, will attack healthy trees. It has been shown to infest urban street trees, natural forests, plantation forestry and fruit tree crops. This beetle has been recorded to cause substantial economic damage in other countries (modelling puts the total economic cost of polyphagous shot-hole borer establishment in South Africa at $27.12 billion).

The environmental impact of polyphagous shot-hole borer in Australia cannot be fully predicted as the susceptibility of many native plant species is not currently known. There are however, many native species that are known hosts in other countries, indicating the potential for significant environmental damage if polyphagous shot-hole borer was to become established in Queensland.

Polyphagous shot-hole borer spreads with the movement of infested plants, wood (including bark, wood chips, firewood, plant mulch, plant prunings and floral arrangements), and machinery (including vehicles) associated with arboriculture, wood processing and handling.

While almost the entire lifecycle of polyphagous shot-hole borer occurs inside the host plant, adult females can fly. The females undertake take a short-range post-mating dispersal flight, typically less than 40m although distances of up to 400m have been recorded in favourable wind conditions, resulting in gradual natural pest spread.

Inspect woody plants with stems greater than 2cm diameter, untreated wood and wood products (including firewood).

Look for:

• tiny entrance holes about the size of a ball point pen tip
• discolouration or staining of wood
• resin, sap or foam associated with borer entrance holes
• frass, a mixture of wood dust and pellets of insect waste material which is usually found below and around an entrance holes
• very small adult boring beetles and larvae inside wood
• branch dieback in living plants.

If you suspect polyphagous shot-hole borer presence, immediately contact Biosecurity Queensland on 13 25 23.

Find out how farmers can protect their farms from plant pests and diseases

• Protect your farm from emergency plant pests
• Understand good farm biosecurity
• Read the biosecurity manual for the plantation forests industry (PDF, 2.4MB)
• Read the biosecurity manual for the avocado industry (PDF, 3MB)
• Visit the farm biosecurity website

Everyone in Queensland has a general biosecurity obligation (GBO) under Queensland's Biosecurity Act 2014. If you think you have found Polyphagous shot-hole borer you must report it and take all reasonable and practical steps under your control to minimise any associated risks.

Report suspected Polyphagous shot-hole borer to Biosecurity Queensland immediately on 13 25 23 or contact the Exotic Plant Pest Hotline on 1800 084 881.