We are on the brink of an ecological disaster, all because of the Shot Hole Borer Beetle. Trees are dying and FABI has indicated that natural control is not in the pipeline at this point.
Sugar Volcanoes Shot Hole Borer Beetle
(Euwallacea cf. fornicata).
The Polyphagous Shothole Borer (PSHB) - an undescribed species of Euwallacea, is a species of Ambrosia Beetle. These beetles belong to the weevil family, and get their name from the symbiotic relationship they have with ambrosia fungi.
The adult beetles carry these fungi into the trees that they bore into, and cultivate gardens of it for the beetle larvae to feed off of. This species of Ambrosia beetle is miniscule – only measuring up to 2mm. The male beetle is wingless and only serves to fertilise the females.
This foreign Borer Beetle was identified in South Africa in 2017 by Dr. Tudy Paap of FABI (Forestry and Agricultural Biotechnology Institute). As infected trees are dying, experts are listing positive identifications in towns as far-flung as Hartswater, Knysna, George, Johannesburg, Pretoria and Durban. This has severe implications for Johannesburg, one of the world’s largest urban forests with an estimated 9-11 million trees.
Judging by the numbers of dead trees killed by Shot Hole Borer Beetles in Johannesburg and Knysna, this could become one of South Africa’s worst ecological disasters. While the beetles are primarily encountered in towns, there is a very real possibility, that they can spread out via tree corridors and start killing trees in the veld.
In a worst case scenario, it could also move into Zimbabwe, Zambia, Malawi and Mozambique. The beetle and fungus has already devastated trees in California and Israel.
Shot Hole Borer Beetle appears to have a cosmopolitan appetite and so far, interpolating from local and Californian reports, 33 indigenous families and 21 positively identified indigenous species could be possible targets.
The beetle carries between 3-5 fungi species with it, of which Fusarium euwallaceae (a newly described Fusarium) is the beetle grubs’ main food source and the primary vector implicated in tree deaths. The other fungi are suspected to aid with the colonisation of a newly infected tree.
The beetle multiplies rapidly. Females lay up to 30 eggs, which take four to six weeks to mature. The male to female ratio can be manipulated by the egg-laying female, so that more egg-producing females are produced that males.
In KwaZulu Natal FABI has discovered that there can be up to 6 emergence episodes per year. The implication is that if you have 1 pregnant beetle in the beginning of the season, you will have 729 million beetles by the end of the year. In a BEST case scenario, that is 364 million females!!!!
The threat of this infestation lies in the Fusarium fungus colonising in the tree and cutting off food and water supply by mechanical blocking of the tree’s system. Some trees will have natural resistance to the fungus, but this we will only discover as we go.
These are trees in which the Ambrosia beetle multiplies. Controlling infestation on these, can go a long way towards curbing outbreaks.
Obviously indigenous host trees will be identified as we go.
This should read “How to identify die-back symptoms of Fusarium Fungus”, as it is actually the fungus that causes the damage visible on the tree.
Currently there are chemical injections done by arborists, but it is expensive and will have to be repeated. There is a company working with nano-lipids which is showing great promise, we will report back within a week or two.
Random Harvest Indigenous Nursery is currently working on a control for this deadly tree pest. You can read more about this in the next article in this series.
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