UK Chestnut Trees in danger alien invaders

Academics from the Universities of Hull and Bristol are asking for the public’s help in keeping an eye on the country’s beloved conker trees, whose beauty is gradually being destroyed by an alien moth.

The horse chestnut leaf miner is an ‘alien’ (non-native) moth which arrived in the UK in 2002. Since then it has spread at a rate of 40-60km per year and now covers half of the country, including much of south-central England, East Anglia, the Midlands and most recently East Yorkshire and Cornwall.

This alien moth has caterpillars that live inside the leaves, forming distinctive patches of damage called ‘leaf mines’.

Up to 700 leaf mines have been recorded on a single leaf and the damage caused by large numbers of larvae can be striking.

Severely damaged leaves shrivel and turn brown by mid summer and fall early, well before the autumn, giving the impression that the tree is dead.

The spread and establishment of the horse chestnut leaf miner is of particular concern because, once established, the moth maintains exceptionally high rates of infestation without any evidence of decline. Although the moths do not kill the trees directly it appears that they weaken the trees, which then produce smaller conkers and may become more susceptible to lethal diseases.

No one knows exactly how far the miner infestation has spread so Dr Darren Evans and Dr Michael Pocock are inviting schools and members of the public to take part in an exciting national web-based experiment to monitor the rate of spread of this ‘alien’ insect and discover the natural pest-controlling insects that might control its spread.

This is the largest project of its kind in the UK and is funded by the Natural Environment Research Council (NERC).

Dr Michael Pocock from the University of Bristol explains: 'We are inviting people from all parts of the country to see if horse chestnut trees in their area have been infested. The whitish blotches on horse chestnut leaves that appear during the early summer are an indication that the ‘alien’ moths have arrived in their area. People can then log the location of the tree, either with or without the indication of alien moths, into our website.

‘The moth is spreading year-by-year and so this will give us the most up-to-date picture of the spread of this 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.’