Weevil species, Cyrtobagous salviniae, has been released into the Crocodile river, in Hartbeespoort, in an effort to tackle the spread of Salvinia minima, commonly known as common salvinia, another invasive alien aquatic plant native to South America that presents a substantial threat to South Africa’s freshwater ecosystems.

Initially recorded at Hartbeespoort dam in 2011, salvinia has since spread across various water bodies in the North-West and Gauteng provinces and has spread to the Limpopo river, which forms the national border with Botswana.

“If we do not control this plant, if it is allowed to spread, we will see it moving into more and more water bodies across the country. Unfortunately, it thrives in polluted systems,” said National Research Foundation’s South African Institute for Aquatic Biodiversity / South African Research Chairs initiative biological control and freshwater alien invasive species management chairperson Professor Julie Coetzee.

The biological control agent, Cyrtobagous salviniae, which was released on Monday into the Crocodile river in Hartbeespoort, was imported from Louisiana, a state in the US that also battles Salvinia minima.

Coetzee has conducted extensive research over several years to evaluate the efficacy of Cyrtobagous salviniae (Florida biotype) as a biological control agent for salvinia.

“This plant, and other invasives like it, block out the sunlight into the water body, which reduces oxygen. Plants in that water body will not be able to create oxygen through photosynthesis. If there is no oxygen, there are no fishes, no crabs, no insects. It completely destroys or alters the aquatic ecosystem,” she added.

The initial release is what Coetzee called a “a small starter population”, with plans underway to rear the weevils at rearing facilities at Rhodes University in Makhanda, as well as at community rearing stations around Hartbeespoort dam, Vaalkop dam and Bronkhorstspruit.

“We have a lot of community partners who have realised the value, the sustainability and the cost-effectiveness of these insects.”

Water and Sanitation Deputy Minister Sello Seitlholo, who released the first weevils at a ceremony on Monday, said that there was a need to tackle challenges at the start of the value chain.

“Water pollution in this country is not something that people want to talk about. [However] every single day, my mantra remains the same: if we do not tackle this, we are going to have a crisis in terms of the quality of what comes out of taps.”

“We will have so many Hammanskraals in this country,” he warned, referring to the Tshwane community that experienced the devastating consequences of poor water quality.

“We all know that it was owing to a deeply polluted river that the Temba water treatment plant could not treat the water to potable standards.”