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What's happened to our conker trees

Public asked for help to identify what is happening to conker trees

Published on: 8 July 2020

Iconic horse chestnut trees are under attack by a highly invasive leaf-mining moth, which has spread across much of the UK in the last 18 years.

Now, researchers at Newcastle University and the UK Centre for Ecology & Hydrology (UKCEH) are seeking help from the public in a new family-friendly, citizen science project that aims to track their spread and examine whether insect predators are helping to keep them in check.

The project is being run by the Conker Tree Science project and builds on research carried out in 2010. Back then, about 2,000 people took part in the first study on the leaf-mining moths and their pest controllers and the results were published in the scientific journal PLOS ONE.

Darren Evans, Professor of Ecology and Conservation at Newcastle University, explains: “We found that insect pest controllers were present across the country in our first survey, but the numbers were too low to control the leaf miner.

“Now, and as part of the International Year of Plant Health, we want to discover what has changed over the past decade: have the numbers of pest controllers stayed at a low level, or are they increasing? This is why we are asking the public again for their help in our new project called ‘Mission: pest controllers 2020’.”

The horse-chestnut leaf-miner (Cameraria ohridella) is a tiny moth slightly smaller than a grain of rice. The moth’s caterpillars eat the leaves from the inside and infected trees become weakened, ultimately producing smaller conkers. At this time of year, they build up in huge numbers in the leaves – it has been estimated that over a million will be present across a single tree - turning the leaves brown and making it look like autumn has come early for the tree.

Up until 13 July, members of the public are being asked to become ‘citizen scientists’ by picking a leaf from a conker tree that is infected with leaf miners, sealing it in a bag and keeping it somewhere cool. After two weeks, the insects inside will hatch out and participants are then asked to count the moths and the natural pest controllers, and send Conker Tree Science their results.

Professor Evans added: “We need lots of volunteers from across the country to take part in order for the ‘mission’ to work. It’s a great way of learning about plant health issues, whilst contributing data to a real research project and, like all our projects, we will keep all participants updated with the results.”

The Conker Tree Science project was co-founded in 2010 by Professor Evans and Michael Pocock, Senior Scientist at UKCEH. 

Full details of the project, including how to sign up, can be found on the Conker Tree Science website at 

horse chestnut leaf miner caterpillar damage
A horse chestnut leaf infested by the leaf miner moth caterpillar

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