THE county’s conker trees are under threat from an alien insect invader, a Wallingford scientist has warned.
In the past 10 years, the horse chestnut leaf-mining moth has spread from London into England and Wales.
The moth, which arrived from the continent, burrows through the leaves of conker trees, causing them to turn brown, shrivel and fall early.
Experts had hoped tiny parasitic wasps that lay eggs in the moth caterpillars would act as natural pest controllers, but a study by the Centre of Ecology and Hydrology in Wallingford has shown wasps are being outnumbered.
The evidence comes from records of leaf damage collected by thousands of citizen scientists in 2010 and 2011.
In the study, volunteers, including hundreds of schoolchildren, reared moths in sealed infested leaves.
Counting how many moths emerged made it possible to assess the impact of the parasitic wasps.
Lead scientist, Dr Michael Pocock, said: “It seems almost like magic for children and other people to put a damaged leaf in a plastic bag, wait two weeks and then see insects – the adult moths or their pest controllers – emerge, but making these discoveries was a valuable contribution to understanding why some animals become so invasive.”