By Elaine Wabwire

 

On 11 October 2023, the Centre for Biological Control (CBC), with Professor Sizwe Mabizela, the Vice-Chancellor of Rhodes University, and Ms Debbie Muir, an official from the Department of Forestry, Fisheries, and the Environment (DFFE), released the weevil Listronotus appendiculatus. Their target waterweed is an invasive alien plant first identified in Makana Botanical Gardens in 2009. Sagittaria platyphylla, commonly known as the delta arrowhead, is an invasive aquatic plant from North America. Significant infestations of this plant have been observed in KwaZulu-Natal, the Western Cape, and the Eastern Cape.

The plant can form very dense stands and often referred to as a nuisance species. The delta arrowhead can clog waterways, causing damage to drains, bridges, and infrastructure. Debbie Muir, the Specialist Programme Manager at DFFE said the delta arrowhead is a biodiversity risk. "It outcompetes indigenous aquatic plants in the system, decreasing the existing biodiversity and making it a water desert," she explained.

Biological control entails introducing a plant's natural enemies into its new habitat. In the case of the invasive delta arrowhead plant, its successful spread in South Africa is partly attributed to the absence of natural predators in the new environment. To address this issue, lead researcher for the biological control programme against the invasive aquatic weed, Dr Grant Martin, travelled to the Mississippi Delta (USA) to find the biocontrol agent Listronotus Appendiculatus.

The aquatic weevil can only carry out its life cycle on this plant, it is host specific.

Dr Martin explained that "the aquatic weevil damages the seeds and flowers of the plant reducing the fecundity of the plant and the overall strength of the plant and reducing its invasiveness." This insect helps control the population of the Sagittaria platyphylla plant in its native range.

Biological control as a control method is a more environmentally sound alternative to herbicides application. Elaborating on the long-term nature of this sustainable approach, Dr Martin emphasised that it won't provide instant results but the benefits far outweigh the time invested. He stated, "We've been doing biocontrol in South Africa for 100 years. We know it works and we've had amazing successes."

He also clarified that eradicating the plant proves extremely challenging and costly, primarily due to its tiny seeds. However, once these biocontrol agents are released and established, they become self-sustaining.

Muir added, "The long-term goal is to reduce the use of herbicides on aquatic weeds and to have all aquatic systems under some level of biological control by 2050."

Professor Mabizela expressed his aspiration, stating, "My vision is for this Centre to become a global hub for those interested in the study of biocontrol." He also emphasised the significant impact of Rhodes University's research and its contribution to achieving Sustainable Development Goals, resulting in tangible, positive change.

Professor Martin Hill, the Director of the CBC, echoed the Vice-Chancellor's message and stressed that the Centre's mission is to influence the global use of pesticides through its research.