Wilkins bunting

CABI is sharing its expertise on biological pest control to try and help save one of Britain’s rarest birds from extinction on the UK Overseas Territory of Tristan da Cunha – the most remote inhabited archipelago in the world.

Dr Norbert Maczey is leading a team of CABI scientists who are trying to find a natural enemy for the invasive alien scale insect (Coccus hesperidum) which has infested several islands of the Tristan da Cunha group and is threatening its only native tree Phylica arborea – home to two endangered bird species the golden wilkins’ bunting (Nesospiza wilkinsi) and the Inaccessible bunting (Nesospiza acunhae dunnei).

It is hoped that small hymenopteran wasps can be released in heavily infested Phylica stands to reduce scale numbers below a damaging threshold and safeguard Tristan’s endemic buntings from ‘imminent extinction’ on Nightingale island and Inaccessible island where they reside.

The work, which will involve testing the efficacy of the control agents under climatic conditions similar to those in Tristan da Cunha but using CABI’s laboratories in Egham, UK, is part of a £300,000 UK Government Darwin Plus Initiative grant in collaboration with the RSPB, Fera and the Tristan da Cunha Government.

Brown scale insect

Brown scale insect (Credit: Corin Pratt/CABI).

Dr Maczey said, “The survival of the endemic buntings of Tristan da Cunha, which have evolved into numerous different forms like the famed finches of the Galapagos, is under serious threat following the introduction of invasive alien scale insects.

“The scale insect egests large quantities of honeydew which promotes the growth of black sooty moulds that smother the trees, reduces seed setting and ultimately kills them. Endemic Nesospiza buntings, which have evolved specifically to specialise on Phylica fruit, are therefore threatened with possibly imminent extinction.

“There is an urgent need to find an appropriate method to mitigate the impact of the scale insects and prevent the total collapse of the Phylica forest.”

Dr Maczey added that biological control has been proven to work for C. hesperidum both in indoor and outdoor environments in the past. In fact, this scale species is generally so well controlled under outdoor conditions by its natural enemies that it very rarely becomes a problem. Therefore, the prospects that the release of co-evolved natural enemies can lower the densities of C. hesperidum significantly leading towards a restoration of the Phylica habitats are high.

“This project will use classical biological control (CBC) as a safe and sustainable approach to rapidly address the problem. CBC has been widely and successfully used against scale insects, including on Saint Helena where endemic gumwoods were threatened with extinction by another invasive scale insect species,” Dr Maczey said.

The next step in the three-year project is to set up cultures of host plants and at least one parasitoid control agent within the quarantine facilities at Egham before a first release is planned for 2021 followed by additional releases until 2024.

Trevor Glass, Tristan Head of Conservation, said, “Nightingale Island is our community’s special holiday island, and the unique buntings are a crucial part of our natural heritage. Much of the island’s forest has already been lost, so this project will be vital for securing the future of both the forest and the Wilkins’ bunting. We can’t wait to get started.”

Additional information

Main image (credit – Peter Ryan): The endangered wilkins’ bunting (Nesospiza wilkinsi).

Find out more from the project page.

RSPB issued a press release regarding this story which can be read here.