Thousands of insects released on the dam

Between 6 000 and 10 000 insects are being released on hyacinth on the Hartbeespoort Dam every week in order to curb the current rapid growth of hyacinth on the dam.

The Centre for Biological Control (CBC) at Rhodes University has set up a large rearing facility, managed by the Harties Foundation, where the insects, Megamelus scutellaris, are being bred nearer to the dam so that they can be released strategically and regularly.

“Together, we have set up 3 tunnels at Redstone Estate, where the agents are currently increasing in number. However, because of the high nutrient status of the water which feeds the water hyacinth growth, rapid increases of the plants are expected from time to time while the insect populations work to catch up. We are also implementing an augmented release strategy where we continuously release large numbers of the insects, from the mass rearing facility at Rhodes University,” said Rudy Joles of the Harties Foundation.

The foundation has in the past week released 2 000 Megamelus insects at the Transvaal Yacht Club and 2 000 at the Schoemansville Oewer Club.

“Due to the effect of the biological control, the cover of water hyacinth fell to as low as 2.5% over the winter of 2020. However, the cumulative effects of the cold winter and the sparse populations of plants that the insects rely on for food meant that the number of biological control insects was greatly reduced over winter. As a result, the plants have grown from the large seed bank that exists within the sediment. Each water hyacinth flower can produce thousands of seeds which remain viable for many years and water hyacinth has been present on the dam for almost 50 years, so there is an extensive established seed bank. The seedlings would not have been exposed to the insects, and have therefore grown rapidly with warmer summer temperatures, causing much concern for the residents of Hartbeespoort.”

In the meantime all private initiatives to manually remove hyacinth from the dam, have allegedly been stopped following a meeting with the Department of Water and Sanitation (DWS) and the Department Environment, Forestry and Fisheries (DEFF). According to information the two departments indicated that they have their own plans for the removal of the hyacinth. Kormorant asked for more information from DEFF but has not received a response yet.