Destructive shot hole borer beetle sighted

The polyphagous shot hole borer

The City of Cape Town can confirm that the invasive polyphagous shot hole borer beetle (PSHB) has been sighted in Somerset West, and is in the process of appointing an experienced invasive plant removal team to remove the infected trees.

Last year, Bolander reported that the polyphagous shot hole borer had not yet been spotted in the Cape( “Shot hole borer in SA, but not yet in the Cape”, Bolander March 14, 2018).

The PSBH infestation was discovered in Oldenland Road in Somerset West by gardeners and environmentalists, who noted that a London plane tree in their garden was ailing and exhibited signs of a PSHB beetle invasion. 

The City’s Invasive Species Unit was contacted last month, and a student with a Master of science degree from Stellenbosch University, who is currently working on the PSHB beetle for his thesis, collected samples from the infested sweetgum (Liquidambar styraciflua) and London plane trees in Oldenland Road for laboratory analyses. 

On Wednesday April 3, after extensive DNA testing, the results of the positive PSHB identification were released in a statement by academic experts from the Stellenbosch University’s Department of Conservation Ecology and Entomology, and the Forestry and Agricultural Biotechnology Institute at the University of Pretoria.

The City confirmed that a limited number of trees in Oldenland Road in Somerset West, specifically London planes and sweetgums, are infested with shot hole borer beetles.

The City is working to remove the trees, and it is critical that the PSHB beetles are not spread during the removal project.

An experienced invasive plant removal team trained in the dangers of vector pathways and cleaning equipment will be appointed to assist the City.

The wood will be chipped on site and carefully removed to a different site for solarisation or burning. 

Report PSHB beetle sightings online 

The City is encouraging residents to report any suspected sightings of a PSHB invasion or fusarium dieback online by visiting the Invasive Species Unit’s shot hole borer reporting tool at www.
capetowninvasives.org.za

Click on “Report a PSHB sighting” to give your details and the location of the infected tree. Residents can also upload images of the tree and entrance tunnels, as this will assist the City to do a speedy identification.

Officials from the City’s Invasive Species Unit and an arborist at the City Parks and Recreation Department will conduct an investigation. 

The website has an extensive database of information about PSHB where residents can learn more about this destructive beetle. 

More about the PSHB beetle

The beetle is the size of a sesame seed and is approximately two millimetres in length. Its symbiont fungal partner is threatened trees across South Africa

It is an ambrosia beetle native to Southeast Asia

It was first discovered in South Africa in 2017 on London plane trees in KwaZulu-Natal’s National Botanical Gardens in Pietermaritzburg

The beetle is invading and poses a threat to exotic and indigenous trees across South Africa

The beetle’s most likely pathway or vector is through the movement of infested wood, originating from dead or dying PSHB infested trees, including wood intended to be used for cooking or heating. 

Lifecycle of the PSHB beetle

The female beetle carries with her three species of fungi, including the pathogen, Fusarium euwallaceae

The adult females burrow into trees to establish brood galleries where they lay their eggs.

They introduce the fungus which colonises gallery walls, becoming a food source for developing larvae and adult beetles. The fungus kills the water conducting tissues of the tree, and can lead to branch dieback, and eventually causes the tree to die

What trees are invaded?

Alien trees infested to date include London plane trees, sweetgums, Japanese maples, Chinese maples, pin oaks, and English oaks

Indigenous trees invaded to date include the coast coral tree, the forest bush willow and the Cape willow

What to do

Burning of the infected wood is the preferred method

Chipping of the wood into small pieces for compost is also recommended, as the heat build-up in the composting process will kill the beetle

Once the tree has been felled the debris should be cleared as soon as possible, and if required, the area should be sanitised

Infested plant material can be placed in refuse bags and sealed. The bags must be put in direct sunlight for solarisation, as the heat from the sun helps to kill the beetle and its larvae.