Toti Conservancy uses weevils to eradicate water hyacinth
About 6 000 neochetina weevils have been released onto the water hyacinth at the Toti Lagoon. The weevils' larvae will bore into the plants, causing them to die. The ultimate goal is for all the hyacinth to die off to bring the weed under control.
TOTI Conservancy has taken an innovative approach to eradicating alien-invasive water hyacinth and restoring ecosystem balance by using nature to combat nature. This initiative got underway on June 25, when members released 6 000 neochetina weevils onto the plants in the Amanzimtoti Lagoon.
Water hyacinth, native to South America, poses a major threat to aquatic ecosystems by multiplying rapidly and covering entire water surfaces, which depletes oxygen levels and kills aquatic life.
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The conservancy’s Pia Visagie said that research shows that they are the world’s number one problematic aquatic plant.
“It’s not just a Toti problem; it’s worldwide. The main reason they are a problem is because they’re not indigenous. We don’t want alien invasive plants taking over because then, for example, birds can’t get to worms and fish in the lagoon for their source of food. These plants destroy our natural ecosystems, and as the Toti Conservancy, that’s what we’re trying to protect,” she said.
Over the years, there have been ongoing efforts by organisations and individuals to physically remove the plants, however, the conservancy has taken a natural approach to suppress its growth and reproduction.
“I got in contact with Rhodes University in Grahamstown which breeds the neochetina weevils which are biological control agents. These weevils are not indigenous to South Africa, hence they have no natural predators in the region, making them effective in controlling the water hyacinth population,” said Visagie.
According to a document from Rhodes University, citing Hardi Oberholzer of the Agricultural Research Council, neochetina eichhorniae / bruchi (weevils) are natural enemies of water hyacinth.
“The larvae bore into the petioles and the crown (growth point) of the plant causing water logging and ultimately death of the plant. Adult feeding causes the leaves of the plant to dry out. Long-term damage results in the reduction of the production of flowers, leaves and daughter plants and stunting of plant growth. Under the correct environmental conditions, these two agents, in combination with the other biological control agents that have been released on water hyacinth, can bring the weed under complete control.”
Once all the water hyacinth is cleared, the weevils will no longer have the necessary conditions to reproduce, and their lifecycle will come to an end.
This is the conservancy’s second attempt at this initiative – the first time, three-quarters of the weevils arrived dead during the four-day transit. “I expect to see visible results within three weeks, based on previous experiences. We monitor the progress daily,” said Visagie.
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