Kent's chestnut trees are under threat after an outbreak of Asian wasps was discovered for the first time in woodland in the county, it has emerged.

The Forestry Commission issued an alert yesterday after a sighting of the Oriental chestnut gall wasp (OCGW) was confirmed in the UK for the first time at Farningham Woods.

The tiny wasp, native in parts of Asia, has been accidentally introduced across Europe but it is unknown how it entered Britain.

Up to 3mm long, the wasp has a black body, translucent wings and orange legs. Experts say it only emerges in June and July but is unlikely to be noticed because of its small size.

Although it has no sting or poses no risk to human health, its larvae causes abnormal growths, called galls, to form on sweet chestnut leaves, leaving it susceptible to diseases.

Severe attacks could result in the loss of trees while damage to sweet chestnuts could have a negative consequence on woodland biodiversity.

Despite only one known sighting at Farningham, Britain's suitable climate and the popularity of sweet chestnut trees has heightened fears of an epidemic.

To make matters worse the pest is parthenogenic, which means male wasps are not needed to reproduce.

Surveillance against the wasps have been carried out in nurseries and orchards since 2006 but yesterday's outbreak remains the only one detected.

A five-kilometere area of affected woodland is being surveyed while investigations are also taking place to see how the pest could have entered Britain.

Galls can be controlled using incesticide treatments but it is unlikely to help deal with widespread outbreaks.

One option to minimise outbreaks in local areas is to harvest affected trees by felling them before they are burned.