Primefact PUB26/308, May 2026, First Edition
Granulate ambrosia beetle (Xylosandrus crassiusculus) is an invasive ambrosia beetle that has spread across many regions of the world. It is considered established in NSW and is an increasing risk to a range of industries including macadamia, avocado, pecan, custard apple, forestry and tree nurseries.
Pest status
Granulate ambrosia beetle (GAB) is an insect pest primarily affecting woody plants. It was first detected in Australia in Queensland 2011 and is now considered established. It is not considered prohibited matter and is not a notifiable pest in NSW. It is, however, similar in appearance and causes similar symptoms to some exotic plant pests, such as polyphagous shot hole borer (Euwallacea fornicatus) which was detected in Perth in 2021 but is not in NSW.
If you suspect polyphagous shot hole borer:
- Call the Exotic Plant Pest Hotline 1800 084 881
- Email: biosecurity@dpird.nsw.gov.au with a clear photo and your contact details
- Complete an online form
There are no GAB specific restrictions on movement of host material into or within NSW, however, there are restrictions on the movement of polyphagous shot hole borer host material, and there is overlap in the host range of these two pest species. Movement restrictions and a list of plants to which they apply can be found in Biosecurity (polyphagous shot-hole borer) Control Order 2023. Description
Adult GAB measure 1.5-3 mm and are dark reddish-brown in colour (Figure 1). Females are larger than males (2.1-2.9 mm long), with stout bodies when fully mature. Males are flightless and rarely found outside of galleries.
Damage
After boring into a susceptible host, GAB inoculates the tunnels (galleries) with a symbiotic fungus (Ambrosiella roeperi). This fungus is not pathogenic but interferes with xylem tissue which impacts vascular transport, resulting in symptoms which include foliage wilting, dieback and tree death.
Although GAB can attack healthy plants, female beetles prefer weakened, stressed plants.
Initial visual indicators of GAB are cylindrical strands of sawdust and excrement (frass) coming out of small-bore holes (1-2 mm in diameter) on the trunk or branches. These “frass noodles” (Figure 2) can be short lived as they are easily dislodged by wind, rain, and irrigation. Peeling back the bark reveals a brown coloured sap exuding from the bore holes. Severe infestations can result in ‘sawdust’ build up at the base of the host tree (Figure 3). The initial infestation may be limited to a small section of the tree but will expand as successive generations reinfest the same host.
Life cycle and behaviour
All four life stages of GAB—egg, larva, pupa, and adult—are generally found together in the tunnel system created by the beetles within the woody material of the host.
Females emerge from infested plants after mating and disperse to colonise a new host by boring tunnels into the sapwood. Adult females carry spores of fungi that are transferred onto the gallery walls and brood chambers during excavation. Only after the fungus has established within the galleries will the GAB lay eggs so that once the larvae hatch they can feed on the fungus (Figure 4).
The complete lifecycle of GAB generally takes between 55-60 days with humidity being important for reproductive success. Continuous breeding occurs throughout the year in the tropics, with up to 2 to 4 overlapping generations.
Recent studies in the NSW Northern Rivers found that winged females begin to disperse in late October until early April, with no beetles found in traps from July to September.
Host range
Over 200 species are hosts for GAB including agricultural crops such as avocado, coffee, custard apple, grape vines, macadamia, mango, peach, pecan, plum.
Nurseries of ornamental woody plants and fruit and nut trees are highly susceptible to infestation due to a combination of high densities of single host species and thin diameter wood of young plants.
Granulated ambrosia beetle has been found attacking Australian native species including Eucalyptus, Grevillea robusta, red cedar and Acacia spp. Severe infestations have been detected in camphor laurel on the NSW North Coast. Overseas, GAB has caused economic damage in stored timber at mills where products have taken too long to process.
Spread and movement
Only adult females have the ability to fly. They generally stay low to the ground and can travel several hundred metres, however when assisted by wind they could travel over greater distances.
The most likely method of long-distance spread is through the movement of either infested planting material or wood. Purchasing planting material from accredited nurseries and not moving untreated wood, such as firewood, reduces the risk of spread.
Management tips
Know if the pest is in your area.
Early detection of GAB requires careful visual observations looking for borer holes and “frass noodles” on trunks and branches. Examination of the bark and wood underneath an infected hole reveals brown discolouration caused by the ambrosia fungus (Figure 5). Digging into the gallery may expose beetles and larvae, however, they are not always present.
Several species of native and invasive ambrosia beetles are present in NSW, many of which are considered only minor pests. These species often produce similar symptoms to GAB and the beetles themselves are difficult to distinguish from each other without expert knowledge of insect diagnostics and access to specialised equipment. If you have plants displaying symptoms of GAB and wish to confirm infestation NSW DPIRD provides insect identification services through the Plant Health Diagnostic Services unit.
Follow up with regular in-crop monitoring for beetle and signs of damage
If you find an affected tree with beetle exit holes, regularly check nearby trees for signs of beetle damage as they usually move onto adjacent trees.
Sticky traps baited with ethanol lures can be used to monitor seasonal activity of ambrosia beetles but are generally ineffective at controlling the pest. Note that ethanol is attractive to a broad range of tree pests, many of which are similar in appearance to GAB.
Yellow sticky traps are available from nursery and garden supply stores. Ethanol lures are available from specialist suppliers of IPM equipment. Traps with lures should not be placed directly on host trees as beetles attracted to them may infest the plant.
Plant health plays an important role in granulated ambrosia beetle management
There are currently no registered chemicals available for the control of GAB in NSW. Minimising plant stress through good crop nutrition and irrigation will reduce crop susceptibility to GAB attack.
Reduce the risk of spreading infected material
To limit the spread of GAB, infested wood should be treated onsite.
Heavily infested trees should be destroyed (burnt) as soon as possible. Trees can be left for 3 to 4 weeks after initial infestation, acting as a trap tree for populations to concentrate, possibly sparing nearby healthy trees.
If you cannot burn, such as during a fire ban, you can finely chip all dead and decaying timber. These can then be incorporated into a composting pile where the temperature ranges between 50 and 65 °C before turning (see NSW DPI Primefact 'How to compost on farm').
Actions to minimise risks
Put in place biosecurity best practice actions to prevent the entry, establishment and spread of pests and diseases:
*Practice “Come clean, Go clean”.
*Manage people, machinery, equipment, plant and soil material coming on and off your property. This can be done by implementing a Biosecurity Management Plan for your farm.
*Monitor crops regularly for signs of borer damage.
*Keep records.