Oak processionary moth - Thaumetopoea processionea

In 2006, larvae of the oak processionary moth, Thaumetopoea processionea (Notodontoidea: Thaumetopoeidae) were found at several locations in London. This species is a major defoliator of oak in Europe. The larvae (caterpillars) feed on the foliage of many species of oaks, including English, Sessile and Turkey oaks (Quercus robur, Q.petraea and Q.cerris). Hornbeam, hazel, beech, sweet chestnut and birch are also reported to be attacked, although mainly when growing next to severely defoliated oaks.

Oak processionary moth larvae aggregating on trunk of an oak
London, May 2007

Group of oak processionary moth larvae feeding on an oak
London, May 2007

Defoliation of oak by oak processionary moth larvae
London, May 2007

Oak processionary moth is a native species of central and southern Europe, where it is widely distributed, but its range has been expanding northwards, presumably in response to climate change. It is now firmly established in northern France and the Netherlands, and has been reported from southern Sweden.

Oak processionary moth - questions and answers

Health risk

Larvae of the oak processionary moth are also a risk to human health. The larvae are clothed in numerous long white silky hairs, but much less evident is the covering of many thousands of much smaller irritant hairs (setae) that contain a toxin. Contact with these small hairs, or their inhalation can result in severe skin irritation and allergic reactions.

These problems are similar to those caused by brown tail moth (Euproctis chrysorrhea), whose larvae also posess irritating hairs. However, oak processionary moth is a more significant problem because once established it tends to be more abundant on urban trees, along forest edges and in amenity woodlands, where there is a high probability of it coming into contact with people.

Pest Risk Analysis

As part of the work to support the Oak processionary Moth Outbreak Management Team a Pest Risk Analysis (PRA) has been prepared. This will form the supporting evidence for action by the Forestry Commission under EU and UK plant health legislation:

Pest Risk Analysis record for Thaumetopoea processionea ^(PDF-181K)

The key conclusion from the PRA is that oak processionary moth justifies being classified as a pest of phytosanitary concern and that the main pathway for longer distance dispersal, especially between countries, is on live plants for planting of hosts of the moth, principally oak trees.

Tree Pest Advisory Note

A tree pest advisory note has been published. It gives further information on the pest and photographs of the main life-cycle stages.

PDF Download advisory note ^(PDF-412K)

Action for 2008

Following the recent launch of the 2008 programme of survey and management against oak processionary moth, a note linking actions to the different parts of the oak processionary moth life cycle has been produced:

Survey and intervention in relation to different phases of the oak processionary moth life cycle ^(PDF-123K)

This provides advice on survey, use of insecticides against younger caterpillars and how to remove nests containing caterpillars or pupae later in the life cycle.

A network of pheromone traps will be set up in London during July so that the distribution of newly emerged adults can be mapped and compared with the results of ground surveys for nests and caterpillars. This combined approach is being coordinated through the oak processionary moth Outbreak Management Team.

Address to contact if you think you have seen this insect

Forest Research
Tree Health Division
Alice Holt Lodge
Farnham
Surrey GU10 4LH

Tel: 01420 22255
Fax: 01420 23653
Email: research.info@forestry.gsi.gov.uk

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