Meet the Trouble-Maker in Our Backyards

Side view of the Polyphagous Shot Hole Borer (PSHB) beetle, Euwallacea fornicatus. Image: Wilhelm de Beer, Associate Professor, University of Pretoria
There is an unwelcome guest killing our trees…and fast! A tiny invasive black beetle from Asia, the Polyphagous Shot Hole Borer (PSHB) beetle (Euwallacea fornicatus), has been introduced into South Africa. The first sighting in Cape Town, positively identified by academic experts and the City of Cape Town Invasive Species Unit, has been confirmed to occur in Somerset West.
Until recently, known PSHB infestation in South Africa are Johannesburg, Durban, Richards Bay, Pietermaritzburg, George, Knysna and Hartwater. The dense urban forest in Johannesburg has been hit particularly hard.
What does this beetle do?
The PSHB beetle, also known as the ambrosia beetle, creates tunnels in the trunks and branches of host trees and lays their eggs inside. It does not feed on the trees, in fact, larvae and adults feed on a fungus that it introduces to its host tree – and this is where the trouble starts. It carries several fungal species with it when it infests living trees, one of which is called Fusarium dieback.
What is Fusarium?
The fungus (Fusarium euwallaceae) is carried by the female beetle from tree to tree and grows in the tunnels made by the borer – it is the fungus that kills the tree. Fusarium attacks the tree’s vascular system and disrupts the flow of water and nutrients to the tree, causing branch dieback and eventually the tree dies.
What are the signs?
Symptoms are unique to each tree species. Nevertheless, signs to look out for are round 1 mm wide entry-holes to beetle tunnels; dark, wet staining; thick gumming; and streaks of white powder or fine sawdust coming from holes.
Which trees are affected?
The beetle bores and spreads Fusarium in both indigenous and non-native trees such as Boxelder, London Plane, English Oak, Chinese Maple are attacked particularly hard.
I think I have a PSHB infestation. What do I do?
Report your suspected PSHB infestation online at the Cape Town Invasive Species Unit’s website – Cape Town Invasives. Click on “Report a PSHB Sighting” at the bottom to give details of the location of the tree. You can also upload images of the tree and entrance tunnels online to assist with speedy identification.
For more information, please read the article by Associate Professor Wilhelm de Beer published on The Conversation.
Sources:
“PSHB Beetle.” PSHB.co.za – Polyphagous Shot Hole Borer. Retrieved from https://polyphagous-shot-hole-borer.co.za/pshb-beetle/. Date accessed 9 April 2019.
“Shot Hole Borer.” Cape Town Invasives. City of Cape Town Invasive Species Unit. Retrieved from www.capetowninvasives.org.za/shot-hole-borer. Date accessed 9 April 2019.
By: Melissa Boonzaaier-Davids