Shot hole borer beetle spotted in Somerset West

By | 2019-04-16T11:21:46+00:00 April 16th, 2019|

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

The PSBH infestation was discovered in Oldenland Road in Somerset West by passionate 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 MSc 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 3 April 2019 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 is working on a plan 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.

More about the PSHB beetle

  • The beetle is the size of a sesame seed and is about two millimetres (2mm) in length. Its symbiont fungal partner is threatening 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 invasive 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 bushwillow 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 kills 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.

How to report PSHB beetle sightings online

The City encourages 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 investigate.

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