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The polyphagous shot-hole borer (PSHB) Euwallacea fornicatus is a beetle native to Southeast Asia. It tunnels into the trunks, stems, and branches of a wide range of introduced and native plants causing dieback (the death of upper-most branches) and ultimately tree death.
PSHB has a symbiotic relationship with the Fusarium euwallaceae fungus, farming it inside the tunnels as a food source for the beetle and its larvae. This fungus blocks the flows of water in tracheids and vessels, and of sugars in phloem, causing dieback.
There are six possible signs of PSHB infestation of trees (not including seeing the beetles which are the size of a sesame seed)
1. Small (approximately 1 mm) perfectly circular holes in the trunk or branches
2. Discolouration or staining of the tree trunk or branches. Town of Cambridge have a great image here.
3. Gumming where resin or sap exudes from the holes, sometimes pushing the beetle out
4. Dieback of the tree (which can be caused by other factors, including Phytophthora dieback infection)
5. Galleries inside the tree branch when broken
6. Sawdust or frass which is exuded from the holes.
Image courtesy of Department of Primary Industries and Regional Development
Image courtesy of Department of Primary Industries and Regional Development
These trees are easily infected and produce numerous female beetles, which can fly up to 400m to infect other trees.
Whether a tree is infested depends partly on its susceptibility, but also on the intensity of attack.
There are three reproductive host tree species in the reserve or in nearby Bold Park.
Infestation of reproductive host tree species can result in production of female beetles that infest other host species. To date they have been removed in Perth, but it may be possible to just remove infected branches.
There are four non-reproductive host tree species in the reserve.
These trees can become infested with PSHB but breeding galleries are not established and trees are not expected to die.
Flooded gums are the main tree in the reserve, being in a parkland setting, often with turf underneath. A reduction in canopy of these trees would greatly impact the nature conservation values in the reserve.
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