Rare bird at risk of extinction saved by parasitic wasp in remote island lifeline

A rare bird, found only on a remote island in the South Atlantic, is being aided in its fight against extinction by a parasitic wasp, according to conservationists.

The critically-endangered Wilkins’ bunting, native to Nightingale Island - part of the Tristan da Cunha group of islands - feeds on the fruit of the island’s only indigenous tree, the Phylica arborea. However, an infestation of an invasive scale insect, accidentally introduced to the island, has been wreaking havoc on the forest, which was also battered by massive storms in 2019, putting the Wilkins’ bunting at risk of extinction.

Surveys conducted in 2017 revealed that there were only 120 breeding pairs of the birds left. As a result, conservationists launched a biological control project, utilising a small parasitic wasp Microterys nietneri, which proved successful in controlling the scale insect, without negatively impacting other species.

The initiative, led by wildlife charity RSPB, environmental and agriculture science experts CABI and FERA, and the Tristan da Cunha Government, has also concentrated on establishing a tree nursery to increase the number of fruiting trees and enhance the island’s biosecurity to prevent similar incidents in the future.

The scale insects feeding on Phylica arborea, a shrub or small tree with needle-like leaves and white flowers, secrete honeydew, which encourages a sooty mould on branches, inhibiting photosynthesis, weakening and eventually killing the tree.

Trevor Glass, head of the Tristan Conservation Department, has revealed: "We hadn’t realised quite how damaging the scale insects were on Tristan, affecting many plants as well as Phylica. No one knew what a scale insect was before this project, but the community are now very aware of them."

Dr Norbert Maczey, an entomologist at CABI, recounted that the first biocontrol wasps embarked on an "epic journey" to their new home. The journey began with a cool bag flight from London to Cape Town, a Covid quarantine hotel room stay, followed by a freezing week-long trip to Tristan and a boat ride to Nightingale Island.

Astonishingly, some of the wasps survived the ordeal. April 2021 marked the inaugural release of these parasitic wasps – which breed inside scale insects leading to their demise. Several releases occurred over the succeeding two years, some meeting with success, according to Dr Maczey.

He confirmed, "Despite the on Tristan frequently being cold, wet and windy, the wasps established surprisingly quickly, parasitism rates of the scale insects are currently high, and the trees are already showing signs of recovery." This intervention seems to offer a glimmer of hope for endangered species as recent surveys in February indicated that despite approximately 80% forest loss, Nightingale Island still hosts an estimated 60-90 pairs of Wilkins’ bunting.

A boost to bunting bird populations might be on the horizon thanks to a major conservation effort involving forest recovery and replanting, conservationists have explained. The initiative, aiming to control destructive scale insects, is very likely to help bunting numbers stabilise and recover.

RSPB's UK Overseas Territories project manager David Kinchin-Smith has confidently stated: "This project shows what can be achieved in turning around the fate of a threatened species. Steely determination, ecological expertise and a large helping of luck have all contributed to the success of this work, but hopefully we, and the wasps, have given the buntings a much-needed lifeline."