Invasive beetle threat

As tiny as a flea, the polyphagous shot hole borer is a type of ambrosia beetle that is currently infesting over 200 tree species around the country. Pictures: S. Bush and Z.Wilhelm de Beer, Forestry and Agricultural Biotechnology Institute.

It’s as tiny as a flea, but the polyphagous shot hole borer beetle is laying waste to forests of mighty trees around the world, and now it’s headed this way. It might already be in your garden.

The bug has been chewing away at Johannesburg’s green lungs, and scientists fear it could soon start doing the same here, not only changing city streetscapes but attacking fruit trees and threatening farms and nature reserves.

Last week, over 100 arborists, landscapers, retailers, growers, ecologists, compost and soil suppliers and Lourensford and Vergelegen wine estates met to discuss how best to ward off the beetle.

They urged Capetonians to check their trees and raise the alarm should they spot the beetle.

The shot hole has shown a preference for oaks, most willows, plane trees, avocado, some acacias and most maples, according to Altus de Wet of the City’s recreation and parks.

According to professors Wilhelm de Beer and Francois Roets, of the Forestry and Agricultural Biotechnology Institute (FABI), most borer beetles live in dead wood, but this ambrosia beetle does not eat wood. Instead, it burrows into living trees, establishing brood galleries where it lays its eggs. It introduces a fungus (fusarium euwallaceae) which becomes food for developing larvae and adult beetles.

This fungus blocks the water-conducting tissues of the tree and ultimately causes its death.

Professor De Beer said that by the time the beetles and fungus had killed a large tree, it could be home to thousands of beetles and when they emerged, the females could fly up to three kilometres and attack surrounding trees.

“They’re unstoppable, but good management can reduce the impact,” said Professor Roets.

“The beetle is sensitive to heat, therefore, the best method of eradication is to remove infested branches. Either burn these immediately or cut into smaller pieces, place in sealed refuse bags and leave in direct sunlight so the heat will kill the larvae and the insect,” he said.

Other municipalities have been slow to introduce control measures. However, the City of Cape Town’s Invasive Species Unit has introduced a management protocol.

Programme manager Chandre Rhoda said they had received 80 sightings of which 21 affected trees had been removed.

“It’s critical that these beetles are not spread during removal. The project contains the biomass and treats tools used in the removal process. The wood is chipped onsite and incinerated,” said Ms Rhoda, adding that the City was creating awareness through Friends and hack groups.

Professor Roets said a further problem was that beetles could fly and can get into clothing, vehicles, and cut wood, increasing their spread.

Large-scale chemical treatment was not an option, but could be used on high value, individual trees, he said.

An insecticide used in America is Imidacloprid, but it’s a prime chemical suspect blamed for bee-colony collapse, according to Mike Allsopp, from the honeybee research section of the Agricultural Research Council.

Professor De Beer said symptoms indicating the presence of this beetle vary from patches of white, pow-
dery wood (frass) around the tree or on the trunk, blotches of oozing resin at the beetles’ entrance hole, and/or small raised lesions on the bark.

Professor De Wet said he was not overly concerned about vines as the bark was too dry for habitation by this beetle. “However, fruit trees and
oaks are a far greater concern,” he said.

Dr Tony Rebelo said the beetle turned up in California in 2003 and Israel around 2008 and there were no reports of infestation in those wine producing areas.

Jean Naude, CEO of Groot Constantia, said according to VINPRO (a non-profit company representing 3 500 South African wine producers, cellars and industry stakeholders) the beetle has not yet been detected in South African vineyards.

Arborist Francois Krige, who cares for trees at Kirstenbosch and Platbos, encouraged companies to train their staff to be on the lookout for the beetle and to ensure cleanliness of equipment, such as chainsaws and vehicles.

Paul Barker, of the Friends of Arderne Gardens in Claremont, has a number of champion trees. He encouraged residents to join iNaturalist and keep up to date with information regarding the beetle.

Professor De Wet said everyone needed to take action to stop the beetle’s spread.

“People should go outside, look at your trees. If you find the beetle, report it. Put pressure on your local authorities to respond,” he said.

Report any sightings of the beetle by email to or phone the City’s toll-free number on 0860 103 089.