Conker Tree Science


The Horse Chestnut Leaf Miner (Cameraria ohridella) is a non-native moth that first arrived in the UK in 2002. Dr Darren Evans and Dr Michael Pocock are inviting people to take part in a national citizen science research project to monitor the rate of spread of this alien insect and discover more about the natural pest-controlling insects that might influence its spread. All you need to take part is a Horse Chestnut tree and a plastic bag.

Since its arrival, the moth has spread at a rate of 40–60 km per year and has now spread across half of the country. Its caterpillars live inside the tree's leaves, forming distinctive patches of damage, called 'leaf mines'. The worst-affected leaves shrivel and turn brown by mid-summer and fall early, well before the autumn, giving the impression that the tree is dead.

The Horse Chestnut Leaf Miner (photo: Rich Andrews)

There are two projects that people can take part in and full details are on the Conker Tree Science website.

Alien moth survey

Dr Michael Pocock, from the University of Bristol, explains: "We are inviting people to see if Horse Chestnut trees in their area have been infested. The brownish or whitish blotches on the leaves that appear during the early summer are an indication of the presence of the leaf-miner. People can then log the location of the tree, either with or without the indication of alien moths, on our online form. The moth is spreading every year, so we need your records to give us the most up-to-date picture of the spread of the moth. Verified records will then be passed to Forest Research to add to its national database, which has been recording the spread of the moth since its arrival in 2002."

Typical 'leaf mine' damage on a Horse Chestnut leaf (photo: Michael Pocock)

Pest controller

Dr Pocock added: "At the beginning of July, we are asking people to take part in a simple, but important, study using just a plastic bag. This will see if their alien moths have been 'zapped' by natural pest controllers. We want people to collect a single infected Horse Chestnut leaf between 3rd and 9th July and put it into the bag. Within two weeks, either moths or tiny parasitic wasps, or possibly both, should emerge. Our citizen scientists can then record what, if anything, comes out of their leaf, and so give us vital data to help us understand why this moth has spread so rapidly."

"As well as providing us with important data, Conker Tree Science is an ideal activity for school children to understand the importance of insects, and biodiversity in general. We want to help to enthuse the next generation of naturalists and ecologists, so please spread the news of our project."

Dr Darren Evans from the University of Hull added: "Nature's form of self-defence against this alien invader is a tiny parasitic wasp which eats the moth caterpillars from the inside out —  the wasps are the natural pest controllers. We think there is a time lag between the moth infesting a tree and the wasps attacking the caterpillars. We need the public's help to test whether this is the case, especially in areas that have only recently been invaded. We hope that our results will help us understand invasive species more generally, which is important as these species are one of the biggest threats to global biodiversity."

Conker Tree Science is the largest project of its kind in the UK and is funded by the Natural Environment Research Council. To find out more and to take part in this experiment visit the project's website.

Written by: Dr Michael Pocock