Scientists are stepping up the fight against an invasive tree pest of sweet chestnut trees – Oriental Chestnut Gall Wasp – the UK’s chief plant health officer announced today (April 26).

Approval has been given for the release of a parasitoid wasp called Torymus sinensis, a natural biological control agent, to help reduce the spread of Oriental Chestnut Gall Wasp in England in order to protect the health of sweet chestnut trees.

This method of natural pest control works by using Torymus sinensis to kill the Oriental Chestnut Gall Wasp, thereby controlling the pest in England.

Oriental Chestnut Gall Wasp was first found in England in 2015. The wasp causes galls on the buds and leaves of sweet chestnut which damage the tree.

In high numbers, the gall wasp can weaken the trees and make them more vulnerable to other pests and diseases, including Sweet Chestnut Blight.

Torymus sinensis is already present naturally in England but in very low numbers.

Further releases of the parasitoid will enable the population to build up to a level to effectively control Oriental Chestnut Gall Wasp.

This method of biological control is used successfully in many countries across Europe.

‘Threats to sweet chestnut trees have increased’

Chief plant health officer Nicola Spence said:

“Threats to sweet chestnut trees have increased as a result of tree pests and diseases such as Oriental Chestnut Gall Wasp and Sweet Chestnut Blight.

The release of this biological control agent represents a huge step towards protecting the health of these trees and will further enhance the resilience of our treescape.”

Today’s announcement follows research commissioned by the Department for the Environment Food and Rural Affairs (DEFRA) in partnership with Fera Science.

The release of any biological control agent is carefully regulated, and the release gained governmental approval after a scientific review, including by the Advisory Committee on Releases to the Environment and a public consultation.

Fera Science will control the release, with a programme of monitoring for the next 10 years.