On Monday, 17 March 2025, South Africa took a significant step toward protecting its freshwater ecosystems with the release of the Cyrtobagous salviniae weevil in the Crocodile River at Hartbeespoort. The Rhodes University Centre for Biological Control (CBC), in collaboration with the NRF-South African Institute for Aquatic Biodiversity (NRF-SAIAB), led the initiative to combat the invasive alien water plant, Salvinia minima, which has rapidly spread and choked water bodies in the region.
The release event was spearheaded by the DSTI/NRF-SAIAB SARChI Chair in Biological Control and Freshwater Alien Invasive Species Management, Professor Julie Coetzee, and attended by Deputy Minister of Water and Sanitation, Mr. Isaac Sello Seitlholo. This marks a crucial intervention to curb the ecological damage caused by Salvinia minima, which blocks sunlight penetration, depletes oxygen levels, and threatens fish populations, tourism, and water security.
Deputy Minister Seitlholo highlighted the longstanding battle against invasive aquatic plants, citing previous costly interventions such as physical removal and nanobubble technology, which have yet to provide sustainable solutions. “For decades, the government has fought against alien invasive plants like water hyacinth and common salvinia in Hartbeespoort Dam, exacerbated by excessive sewage, agricultural runoff, and industrial waste. The introduction of this biological control agent offers a cost-effective and environmentally friendly approach to securing our water resources,” he stated.
Professor Coetzee explained that her team conducted rigorous testing of the Cyrtobagous salviniae weevil (Florida biotype) in quarantine facilities for three to ten years to ensure its effectiveness and safety. The research confirmed that the weevil exclusively feeds and reproduces on Salvinia minima without harming native, ornamental, or crop plants. Approval for its release was granted in late 2024 by the Department of Forestry, Fisheries and the Environment, and the Department of Agriculture, Land Reform and Rural Development.
The weevils were sourced from Louisiana, USA, where they have been successfully used to control Salvinia minima infestations. With authorization from the relevant South African government bodies, Professor Coetzee’s team imported a starter population (229) for local rearing and distribution. “The only impact of the weevils will be positive,” she assured, estimating that visible progress in reducing Salvinia minima at Hartbeespoort’s Crocodile River could be expected within a year.
Failure to control this invasive plant could lead to its further spread across South Africa’s water bodies, particularly in polluted environments rich in nitrates and phosphates from fertilizers, sewage, and animal waste. Such unchecked proliferation would have severe socio-economic consequences, limiting fishing, water sports, and recreational activities, while also disrupting aquatic biodiversity and altering entire ecosystems.
The Deputy Minister acknowledged that broader action is necessary, including working with municipalities in the upper catchment to reduce pollution that fuels invasive plant growth. The Rhodes CBC, NRF-SAIAB and the Department of Water and Sanitation remain committed to addressing the issue from both ecological and economic standpoints.
While only a starter population of weevils was released, the CBC, NRF-SAIAB and its partners will now breed the insects at multiple rearing facilities, including those in Makhanda, Hartbeespoort Dam, Vaalkop Dam, and Bronkhorstspruit Dam. These efforts will support further releases across the country. Additionally, the biological control programme will be closely monitored to ensure its effectiveness and provide a long-term solution for protecting South Africa’s freshwater resources.
