Tradescantia tip beetle released as biological control agent

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The Agricultural Research Council’s (ARC) Plant Health and Protection released the Tradescantia tip beetle in Iphithi Nature Reserve, Gillitts, Ethekwini, KwaZulu Natal as a biological control agent on 13 March. The Tradescantia tip beetle has been released as a biological control in response to infestations of the invasive plant Tradescantia fluminensis, commonly known as spiderwort, from southern Brazil.

Invasion by alien plant species is one of many challenges, capable of affecting crop yields and food security, faced by the agricultural sector. Weed control has a major economic impact on the agricultural sector as large sums of money are spent on the control of invasive species. However, the ARC’s Plant Health and Protection campus has been working on a number of environmentally safe control measures.

In 2013 the ARC initiated a biological control programme to help restrict the invasion of spiderwort, which has become a problem in in several parts of the world including Europe, Australia and New Zealand. The plant forms a thick mat on the ground, particularly in wooded areas, preventing other herbaceous species from growing and impeding the recruitment of forest trees.

The Tradescantia tip beetle was imported into the ARC’s Plant Health and Protection quarantine facility at Cedara in 2014. A breeding population was established in quarantine, and the safety of the beetle was tested using standard international procedures. Indigenous plants, closely related to spiderwort, were exposed to the beetle, and its ability to survive on the plants was monitored. As had been demonstrated in New Zealand, the beetle could only survive, and form a population, on the target weed and is therefore considered safe for release in South Africa.

In 2017 a report, applying for release of the beetle as a biological control agent against spiderwort, was submitted to the Department of Agriculture, Forestry and Fisheries. The report was reviewed by international and local experts, and a permit for release was issued in March 2018. At this time, however, the size of the beetle population in quarantine was too small for release and it has taken a year for the population to increase to a point where a release can be made.

The ARC is to release the beetle at a number of sites where there is plenty of healthy spiderwort, in different habitats, and will monitor it to determine whether it establishes a permanent population that is self-sustaining. If this happens, at some release sites at least, the ARC will assess the effectiveness of the beetle in suppressing the growth, density and spread of spiderwort, and the return of native biodiversity.

“The ARC realises the importance of insects in the ecosystem and how they can contribute to food security and high yields,” said ARC CEO, Dr Shadrack Moephuli. – Press release