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Conker trees facing peril from alien invaders

10 June 2010

Conkers, a favourite playground game in British schools, could soon be just a fond memory if a serious threat to horse chestnut trees continues to spread.

Now 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.

A horse chestnut leaf miner. Copyright Rich Andrews.

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."

The second part of the experiment will start in July, when members of the public can help to record the next stage of the invasion and the appearance of nature's pest controller.

Dr Darren Evans from the University of Hull explains, "Nature's form of defence against this alien invader is a tiny parasitic wasp which eats the moth caterpillars from the inside out - the wasps are 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 recently been invaded."

Dr Pocock continues, "We are asking people at the beginning of July to take part in a simple, but important, study - using just a plastic bag - to see if their alien moths have been 'zapped' by the natural pest controllers. We want them to collect a single infected horse chestnut leaf and put it into the bag. Within 2 weeks either moths or tiny parasitic wasps - or possibly both - should emerge. People can then record on our website 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. We could even predict how well our conker trees will fare in the future."

Dr Evans and Dr Pocock recently ran a pilot study in Bristol city centre to raise awareness about the effect of alien species on biodiversity. They used a large Jenga game to demonstrate that we rely on nature and the fact that, once enough animals and plants are taken away, there can be a catastrophic effect on people.

Dr Evans explains, "Any alien species is a major threat to biodiversity because all organisms live in relation to each other and, once an imbalance occurs, the whole system could begin to unravel. The horse chestnut leaf miner is just one example of how destructive an alien species can be."

To find out more and to take part in this important experiment visit www.ourweboflife.org.uk.

Further information

NERC Press Office
Natural Environment Research Council
Polaris House, North Star Avenue
Swindon, SN2 1EU
Tel: 01793 411561
Mob: 07917 557215

For media enquiries and to arrange an interview with Dr Darren Evans, please contact:

Claire Mulley
Media & PR Manager
University of Hull
Tel: 01482 466943
Mob: 07809 585965

For media enquiries and to arrange an interview with Dr Michael Pocock, please contact:

Caroline Clancy
Press Officer
University of Bristol
Tel: 0117 928 7777
Mob: 07776 170238

Notes

1. The website for the project is www.ourweboflife.org.uk.

2. The horse chestnut leaf miner was first observed in Macedonia in northern Greece in the late 1970s, and was described as a new species of the genus Cameraria in 1986. In 1989 it appeared unexpectedly in Austria and has since spread throughout central and eastern Europe.

Its current distribution includes Belgium, the Netherlands, Denmark, southern Sweden, all of Germany, Poland and the central European countries, and it is currently spreading west through France and south through Italy. Since 2002 it has been reported from Spain, Albania, Turkey, Ukraine, Moldova, Belarus and western Russia. Cameraria ohridella was first found established in the UK in the London Borough of Wimbledon in July 2002.

Dispersal of the moth from infested areas occurs on a broad front through adult flight, assisted by the wind, and through the passive transport of adult moths or infested leaves in or on cars and other vehicles. Transportation by vehicles appears to be responsible for the sudden appearance of the moth in towns and cities a long way from known areas of infestation.

3. Dr Darren Evans is a lecturer in Conservation Biology at the University of Hull. His research interests are the impacts of environmental change on the structure and dynamics of ecological networks and the consequences for plant and animal populations.

4. Dr Michael Pocock is a research fellow at the University of Bristol. His research interests are the ways in which animals and plants depend on each other and how people both benefit from and affect these inter-dependences.

Press release: 25/10

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