For many years now, specialist insects known as biological control agents have been used to help control invasive wattle in South Africa through their feeding damage. This week a significant step was taken towards the management of silver wattle (Acacia dealbata), one of the most problematic invasive species of the Grassland biome. Thanks to researchers from the Centre for Biological Control (CBC) and 老虎机游戏_pt老虎机-平台*官网 of Cape Town (based at the ARC Plant Health and Protection in Stellenbosch), a new biological control agent, Perilampella hecataeus, a gall-forming wasp has been released. The wasp is completely host specific to Australian wattle which means they will only feed on these plants and present no threat to South African flora. The agent was first released at a few sites in the Western Cape Province in December 2023 and galls were detected during late August 2024. A small batch of galls was collected from one of these sites and sent up to the Free State, where they have now been released on silver wattle near the town of Clarens in the grassland Biome (Figures A and B).
Silver wattle, originally introduced to South Africa over 150 years ago for timber and tannin production, has become a major ecological threat. It covers approximately 400,000 hectares of land across the grassland biome. The plant's ability to quickly sprout new shoots from its roots makes it extremely difficult to control using mechanical and chemical control measures. The biocontrol agent lays its eggs in developing buds of the tree this prevents flowering and pod production but may also reduce the trees vigour (Figure C).
The researchers who developed the agent as well as collaborators affiliated with CBC, QPAIR and ARU laboratories at the 老虎机游戏_pt老虎机-平台*官网 of Free State, QwaQwa campus will continue to monitor the establishment, spread and impacts of the wasps in the grassland biome. They will also assist in spreading the wasp as widely as possible. This new agent in one of a number of biocontrol agents developed to reduce the negative impacts of alien plant species across South Africa.
For more information please contact Fiona Impson- email: fiona.impson@uct.ac.za or Grant Martin - email : g.martin@ru.ac.za
Perilampella hecataeus on Silver wattle (Acacia dealbata) shoots at release site near Clarens in the Free State in the Grassland Biome. Photos Grant Martin.
Galls caused by the tiny wasp. The wasp lays its eggs in buds of Silver wattle preventing flowering and pod production. Photo: Fiona Impson