Polyphagous shot-hole borer

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.

Larvae

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

Pupae

• White in colour and similar size to adults.

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.

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 can be confused with other small bark beetles.

They are closely related to:

• tea shot-hole borer (Euwallacea perbrevis), present in Queensland and New South Wales
• Kuroshio shot-hole borer (Euwallacea kuroshio), not present in Australia.

Genetic testing by experts is needed to distinguish the invasive species (polyphagous shot-hole borer and Kuroshio shot-hole borer) from the established species (tea shot-hole borer).

Native to Asia (China, Japan, Thailand, Vietnam), polyphagous shot-hole borer has spread to:

• Argentina
• Brazil
• Israel
• South Africa
• the United States of America.

In Australia, PSHB was first detected near Perth, Western Australia in August 2021, but has not been recorded elsewhere in the country.

Previously, the tea shot-hole borer (Euwallacea perbrevis), a closely related species found in Queensland and NSW, was described as PSHB.  It has since been classified as a different species.

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)
• 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:

• report online
• phone Biosecurity Queensland on 13 25 23
• phone the Exotic Plant Pest Hotline on 1800 084 881

• Protect your farm from emergency plant pests
• Read the biosecurity manual for the plantation forests industry (PDF, 2.4MB)
• Read the biosecurity manual for the avocado industry (PDF, 3MB)
• Learn about on-farm biosecurity

All of Queensland is a polyphagous shot-hole borer biosecurity zone, to prevent the spread of polyphagous shot-hole borer into Queensland.

You need a biosecurity certificate to move a polyphagous shot-hole borer carrier from a state where polyphagous shot-hole borer has been found.

If you think you have found polyphagous shot-hole borer, you must:

• report it as soon as practicable, and
• take all reasonable and practical steps under your control to minimise any associated risks.