The Grootvadersbosch Conservancy has worked on the removal of Pereskia aculeata over the past few years and knows how problematic an alien invader it is. The conservancy used to burn off every stem of the plant which was quite an expensive process. The Grootvadersbosch Conservancy has been working with the Swellendam municipality to manage alien invasives and noticed an invasion in the centre of town. We urgently required an easier way of eradicating the pesky Pereskia, so we contacted Dr. Iain Paterson to aid us with some biocontrol. He posted the biocontrol to us where we could release it at two sites – the first site is at a Swellendam municipality near the mall and the second site is at the Buffeljags Dam.
what is pereskia?
Pereskia aculeata originates from Brazil in South America and thus it has no natural predators in South Africa. It is a creeper plant that can easily outcompete and overgrow indigenous plants especially in forest and plantation areas, leaving them with no access to sunlight, natural pollinators, and water (Invasives SA, 2014). The spread of Pereskia aculeata is problematic as the areas with the infestation will become degraded and will have little growth of indigenous plant diversity over time.
what is biocontrol?
Biological control (Biocontrol) is the use of a natural enemy, usually an insect or pathogen, to control and/or eradicate an alien invasive plant species (ARC, 2014). Biocontrol is an alternative method to control and eradicate alien invasive plant species and is very effective and often used in combination with mechanical control
Luckily for this Pereskia invasion, both biocontrol agents were delivered to us, Pereskia Flea Beetle (Phenrica guérini) and Pereskia Stem-wilter (Catorhintha schaffneri). We released both at the Swellendam municipality site and only the Pereskia Stem-wilter at the Buffelsjag Dam site. Both agents can only survive by feeding on Pereskia. The Pereskia Flea Beetle feeds on the leaves, forming big holes while leaving a trail of brown faeces. The Pereskia Stem-wilter feeds on the plant shoot tips, splitting them open and/or rotting them.
We are very grateful for the incredible scientists who work so hard in developing these agents and so we decided to interview Dr. Iain Paterson who shares his experience in developing a biocontrol agent for Pereskia aculeata.
how and when did you start working on biocontrol for Pereskia aculeata?
Dr. Paterson has always had a passion for nature, he loved plants and animals since childhood. Once he started university, he decided to study both Zoology and Botany. While studying, he discovered an interest in insects, he was fascinated by the idea of using insects as a biocontrol agent, consequently, he decided to pursue Entomology and he then did his Ph.D. on Pereskia aculeata.
What is the process for developing a biocontrol and what beetle species are used to combat the alien, invasive Pereskia aculeata?
Dr. Paterson explained that they experimented with potential Biocontrol insects, which are all indigenous to South America. Five insects were used in the experiment and only two were found successful as a biocontrol. It took him 2 years to prove that the Pereskia stem-wilter beetle (Catorhintha schaffneri) will only feed on Pereskia aculeata and not on any other indigenous plants of Africa.
Why is it so important to develop a successful biocontrol for Pereskia aculeata?
Pereskia aculeata is an alien-invasive vine plant species. Vine plants are almost impossible to remove successfully using chemical or mechanical methods without damaging the surrounding indigenous vegetation. Pereskia aculeata also has a nasty habit of resprouting where it has broken off and any present stem fractions will eventually develop into a new plant. Dr. Paterson once brought a Pereskia stem fraction from overseas within a clip file and, with no soil or water, the fraction grew leaves, displaying its remarkable survivability and durability.
Why does the Pereskia stem-wilter only feed and survive on Pereskia aculeata?
In general, insects are selective feeders, they always seek and select the plants with the most nutrients that their bodies can absorb. In their natural habitat, the Pereskia stem-wilter evolved by only feeding on Pereskia. Here in Africa none of our insects are familiar with Pereskia aculeata and will not feed on them. Without natural pests, Pereskia will outcompete our indigenous plant species and spread rapidly.
In what way can the public assist in reducing the spread of Pereskia aculeata?
The public is advised to learn how to identify Pereskia aculeata and not to plant and grow it within their gardens. In the past, Pereskia was used as a hedge plant in the garden because it grows so effortlessly. If the Pereskia aculeata is removed by hand, all the biomass that is removed and disposed of will resprout. Wherever it ends up, it will create a new infestation so it is advised to let the biomass dry out, or even better, spray it with herbicide and once it turns brown, it should be burned.
What should we, the conservancy and/or the public, keep in mind when using Pereskia biocontrol?
Dr. Paterson states that the Pereskia biocontrol will not immediately eradicate the whole alien plant, the beetles must first establish their population. Once established, the Pereskia infestation will slowly deteriorate over time as the beetles feed on the shoots and roots. This will decrease the spread of the plant and reduce the Pereskia infestation.
How can we obtain the biological control for Pereskia aculeata?
The biocontrol is funded by the Department of Fisheries, Forestry, and the Environment (DFFE) and is provided by the Centre for Biological Control (CBC) of Rhodes University.
The Grootvadersbosch Conservancy can also be contacted if Pereskia is observed so we can track its spread and the success of the agent in its control.
With the help of Dr. Paterson and the biocontrol agents, we are doing all we can to remove Pereskia aculeata!
We thank Dr. Paterson for his time and knowledge regarding Pereskia aculeata and the tremendous journey in creating a biocontrol agent!
GVB Conservancy Staff