Thaumetopoea processionea


Larvae massing on a tree branch.

Oak processionary moth (Thaumetopoea processionea), also known as OPM, is a defoliating pest of many oak species including English, Sessile, and Turkey oaks (Quercus robur, Q.petraea, and Q.cerris). The characteristically hairy caterpillars also feed on the foliage of hornbeam, hazel, beech, sweet chestnut, and birch.

Affected Areas

Areas affected by OPM
Wilting of leaves on a young elm tree.

OPM is already established or quickly becoming established in all areas identified in yellow or orange. West and Southwest London are most severely affected with OPM-infested trees confirmed in the following boroughs: Barnet, Brent, Bromley, Croydon, Ealing, Hammersmith & Fulham, Hounslow, Kensington & Chelsea, Kingston, Merton, Richmond, Spelthorne, Wandsworth, and Westminster.




Visit the Forestry Commission web site for more information on the spread of oak processionary moth.

Lifecycle

Eggs

Eggs are laid from July to early September. Each female lays between 100 and 200 eggs on twigs and small branches in the canopy.





Larvae/Caterpillars

Oak processionary caterpillars can be found from April to June. There are six stages during the caterpillar feeding cycle with caterpillars getting progressively bigger during each stage.

Stages 1-3: Caterpillars are very small when they hatch, around 2mm long, and are still less than 1cm by the time they reach the third stage.

Stages 4-6: Caterpillars spin silken nests and the larvae eventually moult to the pupal stage within those nests. During this phase, larvae may also be seen massing on the trunks and branches of trees and moving in the characteristic processions that give the moth its common name.





Adult Moths

Adult moths have a wingspan of around 30-32mm and grey forewings suffused with white and some darker grey markings. This coloration provides an effective camouflage against the bark of oak trees on which the adults often rest.

Symptoms

OPM effect on tree health
Any type of defoliating insect can have a serious impact on tree health, and OPM is no exception.

Large populations of OPM caterpillars can completely strip the leaves from a tree. Loss of leaves is unsightly and also reduces photosynthesis, thereby reducing the energy a tree has to grow. In a weakened state, the tree will be more susceptible to other pests, disease, and environmental conditions.

Control

Before treating OPM, the first step is to look for infestations and confirm the presence of caterpillars. If found, there are a variety of treatments available for affected trees, including:

Biological control

Biological control is a method of keeping pests below damaging levels using natural enemies (such as Bacillus thuringiensis) and usually involves an active human role in the process.




Insect growth regulator

Insect growth regulator is a chemical that inhibits the life cycle of the insect.




Synthetic insecticides

Synthetic insecticides are botanical pesticides based upon plant extracts that are used to manage pests.


Removal of OPM caterpillars or larval nests is another method to control the spread of this pest. Caution must be taken when coming in contact as there are many risks to human health.

Below is a table that shows the recommended treatment options for the life-cycle stages of development of the oak processionary moth.

 

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Egg

 

 

 

 

 

 

 

 

 

 

 

S1

 

 

 

 

 

 

 

 

 

 

 

 

S2

 

 

 

 

 

Spray Treatment

S3

 

 

 

 

 

 

 

 

 

 

 

 

S4

 

 

 

 

 

 

 

 

 

 

 

 

S5

 

 

 

 

 

 

 

 

Survey and nest management

 

S6

 

 

 

 

 

 

 

 

 

Pupae

 

 

 

 

 

 

 

 

 

 

 

 

Adult

 

 

 

 

 

 

 

Pheromone trapping for males

S = Life cycle stage. Timing can be heavily influenced by prevailing climatic conditions. The table provides an estimation and should be used only as a guide.


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