The future of conker contests in Sussex could be under threat from an invasion of moths.

The damage caused by horse chestnut leaf-mining moths currently spreading across the UK could herald an end to the playground game.

Experts are warning it is only a matter of time before the insects begin attacking the large population of horse chestnuts in Sussex, as they have already done in Oxfordshire, Hertfordshire, London and Surrey.

The Royal Horticultural Society says the moths, found in parts of Europe and Asia, lay eggs which hatch on the horse chestnut trees and eat the leaves. This can hamper the trees' growth and ability to produce conkers.

Very little can be done to stop the invasion because horse chestnuts are normally too tall to spray with insecticides and the moths have no effective natural predators in England.

Experts at Forest Research in Hampshire, associated with the Forestry Commission, said it was inevitable the moths would come to Sussex.

Christine Tilbury, Forest Research's advisory entomologist, said removing leaves around horse chestnuts during the autumn and winter months could help.

She said: "The moths lay eggs on to the leaves. They form into caterpillars and it's these that do the burrowing into the leaves.

"They then turn into a chrysalis, like a butterfly, and that takes place on the leaf. By the end of the summer, we have had several generations of moths. We have certainly already had three generations in the UK. You can get up to five in hotter climates.

"The end of summer will be the final generation. Instead of emerging as a moth, it remains as pupa and becomes a caterpillar then a chrysalis in the spring. A new adult eventually emerges.

"An infected tree sheds leaves that have got pupae on them. Removing the leaves effectively takes away the pupae that will start next summer's first generation."

She said the Forestry Commission put out an exotic pest alert when the moths were discovered in France in 2002.

Mrs Tilbury said: "It's inevitable they will spread to Sussex but how long it will take I do not know."

She said the moths could travel long distances on the wind or in vehicles.