Meet the Tiny Hoppers Saving Hartbeespoort Dam

Every Thursday Dr Kelby English makes her way to the Hartbeespoort Dam with 20,000 tiny insects packaged carefully in translucent containers. She, along with some local residents, then release the tiny insects onto the green carpet of invasive water hyacinth which now covers almost 40% of the dam.

English is a post-doctoral research fellow at Rhodes University. She works at the Centre for Biological Control (CBC), a research centre based in the Department of Zoology and Entomology at Rhodes. Their research focuses on the ecological dynamics of invasive pests, aquatic weeds and terrestrial weeds. The CBC has been releasing bugs into Hartbeespoort Dam since 2019.

The Megamelus Scutellaris, commonly known as the water hyacinth planthopper, feed on the hyacinth.

The water hyacinth planthoppers measure around 3mm. They pierce the invasive plant tissue, damaging cells which reduces the plant’s buoyancy and causes it to rot. The insects render the invasive plant unable to produce flowers, reducing the seed bank in the dam.

Water hyacinth, an invasive aquatic plant, is native to South America and has been present on Hartbeespoort Dam since the 1960s.

Polluted water flowing into the dam has increased nutrient levels creating a fertile environment for these invasive plants.

Millions of seeds have been deposited into the dam by flowering hyacinth. These seeds, which remain viable for about 20 years, germinate during spring, when warmer temperatures and increased rainfall create ideal conditions.

“Stopping the seed bank from growing is one of our main aims and we are succeeding because the biocontrol agents are preventing the plants from flowering. But this is a process that will take years, so people need to be aware of that,” said English.

Magalies Water was appointed by the Department of Water and Sanitation to develop a remedial program to rehabilitate Hartbeespoort dam. It has now officially contracted the CBC to scale up its biocontrol program.

The CBC, working with communities near the dam, has established ten rearing stations where thousands of planthoppers are bred close to the dam and released onto the hyacinth regularly by the communities.

“People often question how these tiny bugs can help with what seems like a massive problem. They even ask if the biocontrol is actually working. But they are the most effective, environmentally friendly and cost-effective solution. We are seeing reduction in the hyacinth cover as well as the seed bank,” said English.

The increased growth of the hyacinth has prompted the National Sea Rescue Institute (NSRI) to issue a warning to the public about going to the dam with boats as the hyacinth can damage motors.

“We are asking the public to carefully consider whether it is safe to go out on the water,” said Arthur Crewe, NSRI Hartbeespoort Station Commander. “If your craft becomes trapped in the hyacinth, your rescue options are limited. Even our rescue vessels suffer damage attempting to get through, and in some cases, rescues are extremely challenging.”

Upstream pollution flowing into the dam from municipalities dumping sewage as well as industrial and agricultural pollution remain the biggest challenge to the health of the water and aquatic life at the Hartbeespoort dam.

David Magae from Magalies Water said that the water entity is continuing its work on rehabilitating the dam.

“It is common cause that the current situation of the growth of the hyacinth and salvinia have an adverse effect on the amount of oxygen on the waterbody which can also result in the death of other aquatic species, such as the fish found in the dam.

“Magalies Water has previously commented publicly on the high levels of loaded pollutants that enter the dam which also contributes to the sprawling growth of the hyacinth water plant,” said Magae.

During the peak season for water hyacinth growth the invasive species can cover about 40% of the dam’s water surface.

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