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

The economic impact of the polyphagous shoot drill in South Africa is enormous R275 billion over the next ten yearsand municipalities will bear the brunt of this cost if nothing is done to stem the tide, say Stellenbosch University (SU) researchers.

The shoot 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 worldwide. While most of South Africa’s most popular invasive species are problematic in rural areas, this aggressive invader will have the greatest impact on trees in urban areas.

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

Rather than basing their findings on existing data, the team used a modeling approach based on predicted impacts; thus, he wanted to simulate the possible future impacts of this invader, so that it does not spread further if nothing is done.

Professor Francois Roets, an ecologist from SU’s Department of Conservation Ecology and Entomology and one of the authors, said a tree-rich town like Stellenbosch would lose 20,000 of the grand old oaks and plane trees lining the streets. In Somerset West, where the gunshot borer was first detected four years ago, more than 10,000 trees have already been infected and some oaks are dying.

The data shows that by 2020 to 2030, if nothing is done to stop the spread, 65 million urban trees will have to be removed and disposed of safely. The economic impact of business as usual during this period will be R275,000 billion, the researchers said.

“Municipalities need a national policy and a coordinated strategy to stop this beetle in its tracks”, he warned. So far, the polyphagous borer is still not listed in the Alien and Invasive Species Regulations, making it difficult for municipalities to react effectively,” said Professor Martin de Wit, economist at SU’s School of Public Leadership.

To date, there are no fully tested and approved insecticides or fungicides registered in South Africa to effectively treat shoot borer infestations, at least not for urban trees. Anyone who tells you they’ll save your tree with chemicals and fungicides is likely lying and breaking the law,” Professor Roets said.

“A coordinated strategy to combat the invasion in South Africa will require a review of legislation and the creation of policies on biological invasions. Currently, there is no coordinated management of invasive species in urban ecosystems, critical oversight.’


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