Maties student takes on tree-killing beetle
A Stellenbosch doctoral student is at the forefront of the battle to save SA’s trees and forests from an invasive Asian beetle that kills them.
Heather Nependa has made Vergelegen wine estate in Somerset West the frontline in the war on the polyphagous shot hole borer, after the beetle was detected there in February.
Vergelegen is home to five camphor trees planted by former governor of the Cape Colony Willem Adriaan van der Stel in 1700, and a 300-year-old English oak, believed to be the oldest tree in SA.
With the assistance of two other students, Nependa has catalogued more than 1,000 Vergelegen trees. The oldest oak is festooned with repellant pouches intended to keep the beetles at bay.
Nependa, a student in Stellenbosch University’s conservation ecology and entomology department, is working with the estate on a range of other interventions aimed at saving thousands of trees nationwide from the ravages of the beetle. The research is part of her doctoral thesis.
Vergelegen’s risk and commercial manager, Leslie Naidoo, said since being discovered in SA in 2017 the polyphagous shot hole borer beetle (PSHB) had spread to every province except Limpopo.
Nependa said the wine estate’s history and biosphere make it suitable for her research, which aims to establish amonitoring and early detection scheme and learn more about the life cycle of the beetle, how it spreads, and the symptoms of damage on
different species. She also wants to unravel the relationship between the beetle, its associated fungus and the trees it kills, leading to evaluation of possible lures, repellants and pesticides.
“Two types of pesticides — insecticides and fungicides — will be tested and their side-effects and appropriateness thoroughly reviewed. [We will also be] collecting and analysing data in the field for a PSHB management plan geared to South African conditions,” she said.
Nependa uses two types of trap to monitor and collect the beetle. One uses 2l plastic bottles filled with a chemical lure and tied to 1.5m steel rods. There are 50 of these and they “possibly” keep the beetles away from the trees.
The second trap has been 3D-printed and is secured over holes made by the beetles. Steel mesh is placed over each opening to stop them from escaping. Traps are inspected every two weeks and the contents delivered to the university for identification.
“An important next step is to map out invasion pathways and determine what drives dispersal,” Nependa said.
“Temperature-logging buttons will be placed at each of the sampling sites to help track how climate changes affect beetle dispersal. This data will also be important for lab experiments on beetle and fungus biology and physiology.”
The project will run until June 2022 and the findings will be documented and made available to interested parties.