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Home Cape Town News City’s tiny secret agents on a mission to root out alien invasive plants

City’s tiny secret agents on a mission to root out alien invasive plants


Councillor Brett Herron, Mayoral Committee Member for Transport and Urban Development, visited the City of Cape Town’s Insect Mass Rearing Facility in Westlake today to meet the City’s biocontrol agents. More than 243 000 biocontrol insects, also known as agents, have been reared for release into the environment to destroy alien invasive plants across the city. This innovative project forms part of the City’s efforts to create jobs and manage invasive plants to ensure a more sustainable environment.

Since its launch in September 2014, the City of Cape Town’s Invasive Species Unit’s Insect Mass Rearing Facility in Westlake has been using an organic, cost-effective and environmentally safe biological control method to curb invasive plants by breeding and releasing their natural enemies: insects.

To date, the facility has reared more than 243 000 insects for release across the city to help root out alien invasive plants (AIP).

The facility currently rears agents for four aquatic AIPs, namely water hyacinth, parrot’s feather, kariba weed and water lettuce, which are considered the worst invasive weeds in South Africa. The facility also rears biocontrol agents for one terrestrial AIP, the prickly pear (Opuntia monocantha).

The Cape Town Biological Control Programme is a partnership between the Department of Environmental Affairs and Rhodes University’s Department of Entomology.

During his visit to the facility, Councillor Brett Herron, Mayoral Committee Member for Transport and Urban Development, saw first-hand how the insects are collected and packaged, ready for their next mission.

‘Today’s visit to the insect-rearing facility has been most fascinating. In order to rear the agents, our team actually grows the plant which the agents are intended for. The aquatic invasive plants are grown in the artificial ponds at our facility and this is also where the agents grow and complete their life-cycle. The agents are then collected them from these ponds when they are ready to be released on their mission,’ said Councillor Herron.

Each of the insects are physically counted and then placed in plastic containers. Within hours they are transported and released on the specific invasive plant.

Generally, the insects are released every two weeks. The number of insects that are released depends on the size of the mission field. Successes in the field depends on the season and other activities that may be taking place in the area.

‘When the conditions are right and the optimal number of agents are released onto the invasive plant, it can take only a few days for the agents to start establishing on site. Once they have ‘set up camp’, it could take weeks for the agents to destroy the plant, depending on the size of the area that needs to be covered. It is important to note that, after the agents have been released, they also continue to propagate and complete their life-cycle. Their offspring also continue to destroy the targeted invasive plant until the whole invasive plant has been destroyed and then their life-cycle comes to an end,’ said Councillor Herron.

The Westlake river, which was previously choked with kariba weed, is an example of a mission accomplished. Please see the before and after photographs.

Biological control is increasingly becoming a cost-effective method of control in the war against infestations of invasive aquatic weeds and prickly pear.

Other methods include the removal of aquatic weeds with machines, labour-intensive manual control or chemical control. The best successes are realised when biocontrol is employed as part of an integrated control approach, using a combination of one or more of the available methods.

In addition to the environmental benefits, the biocontrol project provides a platform for green job creation, skills development and education.

Some of the staff have been trained at Rhodes University, the leaders in biocontrol research in South Africa. Five staff are currently employed under the Expanded Public Works Programme (EPWP) to assist with the day-to-day activities in the biocontrol facility.

The activities include, but are not limited to, cleaning the facility (including the artificial ponds), making sure there is fertiliser in the ponds and collecting (and counting) the agents for release in the field.

The EPWP workers are also trained to lead tours, information sessions and provide environmental education through the facility for school learners, community friends’ groups and other interested groups.

‘Since the inception of the biocontrol project, a number of people have been trained on how to rear and collect the biocontrol agents as well as to release them in the field. We are very impressed by the commitment and the passion that the staff have for this project.

‘We are also very proud to know that the public, especially our learners from various schools, are receiving first-hand experience on the application of biological control as an exciting part of invasive plant management. We really hope that through the interactive education around controlling invasive plants, we would inspire and encourage the next generation of environmentalists or nature enthusiasts.

‘Overall this cost-effective, natural and innovative biocontrol project is very exciting. I am looking forward to seeing more successes because by reducing invasive plants, we are making way for indigenous species, and this will contribute to creating a more sustainable environment for all of us to enjoy,’ said Councillor Herron.









Captions for the photographs: 

Featured Image:

Biocontrol agent (leaf-eating beetle; Lysathia sp.) on the parrot’s feather (Myriophyllum aquaticum).

Image 1:

From left: Sabelo Lwana, EPWP Community Liaison Officer, with Councillor Brett Herron, Mayoral Committee Member for Transport and Urban Development; and Chandre Rhoda, the manager for the City’s Invasive Species Programme, inspect the water lettuce for biocontrol agents.

Images 2 and 3 – Westlake River:

Before: Kariba weed infestation in the Westlake river before the release of the agents.

After: Kariba weed infestation under control after the biological control agent was released and established.

Issued by: Media Office, City of Cape Town

Media enquiries: Councillor Brett Herron, Mayoral Committee Member for Transport and Urban Development, City of Cape Town,

Tel: 021 400 1298 or Cell: 082 518 3264,

Email: brett.herron@capetown.gov.za (please always copy media.account@capetown.gov.za)

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