The polyphagous shot hole borer beetle, or PSHB (Euwallacea fornicates), originating in Southeast Asia, is a highly dangerous species. Recently discovered in Johannesburg, it is capable of causing a great deal of damage to indigenous trees in South Africa.

Although the beetle itself doesn’t kill the tree, the fungus that accompanies the beetle does by targeting the tree’s vascular system and inhibiting the flow of water and nutrients within the tree.

Only 2mm in length, the shot hole borer is associated with various types of fungi, one of which is Fusarium euwallacea. The beetle shares a symbiotic relationship with this fungus, which is the it’s main source of food and associated with the wilting of trees. Other types of fungi are also believed to help the beetle’s colonisation of newly infected trees.

Charles Reitz recently came upon an unidentified fungus on Milkwood trees in the Knysna area which he found concerning and had reason to believe could be caused by the notorious shot hole beetle that has been identified in KwaZulu – Natal and Gauteng and is threatening the survival of large numbers of indigenous and exotic trees in those areas.

“My main concern arose when I was pruning Milkwoods in Knysna and I noticed hundreds of little beetles boring into the bark, forming what appeared to be nests or colonies embedded in the outer part of the bark. After looking at Milkwoods in different areas of the Garden Route I found the beetles on almost every specimen.

I consulted other tree experts, but no one could confirm whether or not the beetle I have observed is in fact the polyphagous shot hole borer. I have also received no feedback from the relevant government authorities on my observations and concerns.

It could be possible that the Garden Route fires of 2017 had a trigger effect as I did not see this pest on Milkwoods or other species before the blaze. Yet, it appears the Milkwoods are surviving this onslaught as I have found that the tiny holes created by the beetle do heal over a period of about two months, which could suggest that it is a wood borer beetle of another nature. But the beetles and their effects I have observed certainly seem to be the polyphagous shot hole borer.

Five years ago contractors were deployed to fell a large number of oak trees in Knysna due to the spread of alien ambrosia beetles. The question remains was this the start of PSHB in the area and if so why is it reported to only have been discovered in 2017?

My recommendation to the public is if you observe any symptoms in both indigenous and exotic trees that suggest the PSHB, take photo’s and report it to us on 082 424 0055 or contact your local DAFF authority.”

shot hole borer beetle

Borer beetles found in Milkwoods along the Garden Route

  • Below information taken with permission from Greenpop

The beetle’s discovery in South Africa

Dr Trudy Paap of the Forestry and Agricultural Biotechnology Institute (FABI) initially discovered the beetle in South Africa on a routine study of diseases in KwaZulu-Natal Botanical Gardens in Pietermaritzburg in 2017 where she found a series of infested trees. This led to the identification of the beetle and the regions in which infestations are taking place.

The shot hole borer, along with its fungus, has caused large scale damage to trees in the United States, specifically California, as well as some regions of the Middle East. In South Africa, the beetle has been found in Sandton, which is particularly concerning because Johannesburg is believed to be one of the world’s largest urban forests with an estimated 10 million trees. Judging by the number of trees the beetle has killed in Johannesburg and in Knysna, the shot hole borer could potentially be one of South Africa’s largest ecological challenges. The borer has infested more than 200 tree species worldwide.

How is the shot hole borer identified?

The beetles themselves are too small to detect, but what can be done is to identify infected trees, the symptoms of which vary from one tree species to another, and there are many signs that indicate that a tree is infected, including wilting, dead branches, entry and exit holes in the bark of the trees, shotgun-like lesions on the bark at entry and exit holes; sugar volcanoes on the bark at entry and exit holes; blotches of oozing resin on the bark at entry and exit holes, and wood frass (wooden powder) on the bark at entry and exit holes.

Polyphagus shot hole borer beetle (Euwallacea fornicates)

Types of trees being infected

The borer infects more than 200 tree species from 28 plant families, so it would be difficult to list all of the tree species. However, some of the important commercial crops that are susceptible, and that we should know are susceptible, are avocado (which suffered heavy damages in California), pecan, peach and orange trees, as well as grapevines.

What can we do?

So far, no remedy has been discovered and insecticides are ineffective against the PSHB because the beetles drill deep into the wood. However, the only form of resistance against the beetles is for us to cut down and burn the wood to prevent the spread of these beetles. Cautionary procedures should be taken when transporting or handling plants and trees. It is not advisable to move plants that show signs of infestations, but rather that infected plants are cut into smaller pieces, sealed, and kept in direct sunlight. The heat from the sunlight will lead to the insect and its larvae’s death. The public can also aid in the management of the spreading by reporting any signs of infestations to FABI.

South Africa is considered to be the biodiversity capital of the world and is a host to 299 species of mammals and 858 species of birds, many of which are heavily dependent on trees as a source of nutrition and sustenance. Therefore the shot hole borer truly does pose a threat to what makes South Africa unique. For this reason, an immediate response to eradicate this threat is imperative to help preserve the beauty that is South Africa.