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Many invasive cactus spread aggressively, to the detriment of other plants and the whole ecosystem.
Photo: C Mannheimer
Biocontrol agents make infected cacti unhealthy and help to control their spread.
Photo: C Mannheimer
A healthy Imbricated cactus. This species is aggressively invasive, forming impenetrable stands.
Photo: C Mannheimer

Invasive alien plants biocontrol

The Society embarked upon an ambitious project to introduce two different types of cochineal bugs and a cactus mealybug into Namibia at designated areas, one of which was at Farm Windhoek, a popular biking and walking area on the periphery of the city. The bugs feed on the sap of specific cactus species, making the plants unhealthy and reducing flowers and fruit, and by this means help to control its spread.

The project was spearheaded by Coleen Mannheimer and Prof Iain Paterson of the Centre for Biological Control at Rhodes University. Dr Paterson made two research trips to Namibia to see which cactus species are most problematic here, and to inform us about the introduction of the biocontrol agents. In August 2019 he returned with the biocontrol agents and several sites were infected. The project is being carefully monitored by staff and postgraduate students at the Namibia University of Science and Technology. The time and expertise of these students has been partially sponsored by the Botanical Society.

Together with Namibian Chamber of Environment, who provided supportive funding, the committee liaised with government and municipal authorities to obtain permission to embark upon a pilot scheme, which is still being evaluated with regard to the degree of success. This project has exciting possibilities for development beyond the capital to combat these destructive species, which cause injury and death to livestock, birds, and other animals, and invade large areas that can subsequently not be used by game or livestock. The spread of such cacti in some rural towns is alarming. In Kenya cactus have become a huge problem, even for large animals such as elephants.