This tiny beetle is eating its way through tree-rich towns in South Africa – and is set to cost the economy R275 billion

The potential economic impact of the polyphagous shot hole borer in South Africa amounts to a whopping R275 billion over the next ten years, and municipalities will have to bear the brunt of this cost if nothing is done to stem the tide, say researchers at Stellenbosch University (SU).

The shot-hole borer was first detected in South Africa in 2012 and has since spread to eight of South Africa’s nine provinces, making it the largest current outbreak of this invasive pest globally. Whereas most of South Africa’s most notorious invasive species are problematic in rural areas, this aggressive invader will have the largest impact on trees in urban areas.

This estimate is the result of a collaboration between economists, ecologists and other scientists at Stellenbosch University and the University of Pretoria.

Instead of basing their findings on existing data, the team used a modelling approach based on forecasted impacts – thus seeking to simulate possible future impacts of this invader if nothing is done to prevent it from spreading further.

Prof Francois Roets, an ecologist in SU’s Department of Conservation Ecology and Entomology and one of the co-authors, said a tree-rich town like Stellenbosch stands to lose 20,000 of the big old oaks and plane trees lining its streets. In Somerset West, where the shot hole borer was first detected four years ago, more than 10,000 trees have already been infected and some of the oak trees are now dying.

The data shows that if nothing is done to halt its spread from 2020 to 2030, 65 million urban trees will have to be removed and safely disposed of. The potential economic impact of business as usual over that period will be R275 billion, the researchers said.

“We need a national policy and coordinated strategy for municipalities to stop this beetle in its tracks,” he warns. To date, the polyphagous shot hole borer is not yet listed under the Alien and Invasives Species Regulations, making it difficult for municipalities to react effectively,” said Prof Martin de Wit, an economist at SU’s School for Public Leadership

To date, there is no thoroughly tested and approved insecticide or fungicide registered in South Africa to treat infestations of the shot hole borer effectively, at least not for urban trees. Anyone who tells you they will save your tree with chemicals and fungicides is likely lying and will be breaking the law,” said Prof Roets.

“A coordinated strategy to deal with the invasion in South Africa will require a revision of legislation and the creation of policies relating to biological invasions. Currently, there is no coordinated management of invasive species in urban ecosystems, a critical oversight.”

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This tiny beetle is eating its way through tree-rich towns in South Africa – and is set to cost the economy R275 billion