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Pine processionary moth - (Thaumetopoea pityocampa)

Pine processionary moth - LarvaPine processionary moth (PPM) larvae (caterpillars) feed on the needles of pine trees and some other conifer tree species. In large numbers they can severely defoliate trees, weakening them and making them more susceptible to attack by other pests or diseases, or to environmental stress caused by drought or excessive moisture. PPM, like its close relative the oak processionary moth (OPM), gets its name from its distinctive habit of moving about in nose-to-tail processions.

Like OPM, PPM caterpillars represent a public health hazard because they have thousands of hairs which contain an urticating, or irritating, protein called thaumetopoein. These hairs can be blown by the wind into contact with people and animals, resulting in painful skin irritations and rashes and, in some cases, allergic reactions in some people and animals.

PPM is not currently known to be established in the UK, but  it has been extending its range across Europe towards the English Channel. We and other plant health authorities across the UK are taking steps now to consider how the UK can best prevent, or minimise the risk of, its entry to the UK. (See "Action", below)

Sightings in UK

The pest is not known to be established in the UK. However, one transient population of larvae was found in a UK nursery in 1995 on Scots pine plants which had been imported from Italy in 1994. The affected trees and soil were treated, and subsequent monitoring did not detect the pest. Single adult moths have occasionally been found in southern England: in 1966, in August 2013 and in summer 2017. The latter two were found in south-coast locations, and had probably been blown across the Channel from France. However, the origin of the 1966 moth, which was caught in a light trap in Berkshire, is not known.

Origin

It is native to, and until recently was only found in, the Mediterranean region, North Africa and some areas of the Middle East and southern Europe.

Distribution

Possibly as a response to climate change, PPM has been expanding its range north through France since the 1990s, and is now breeding near Paris. Long-distance movement is thought to be associated with pupae being carried in the growing medium or soil of infested plants.

The full list of countries where it has been recorded as established is: Albania, Algeria, Austria, Bulgaria, Croatia, Cyprus, France (including Corsica), Greece (including Crete), Hungary, Italy (including Sardinia and Sicily), Libya, Macedonia, Montenegro, Morocco, Portugal, Serbia, Slovenia, Spain (including the Balearic Islands), Switzerland, Syria and Tunisia.

Means of spread

a. Movement of plants for planting
There is a risk of larave, or caterpillars, being moved with plants for planting being brought into the UK. However, the white silken nests which the caterpillars form in trees in winter are very obvious, being sometimes as big as a football. In most cases, these nests and any associated caterpillars would be clearly visible during winter and spring when plants are usually imported, greatly lowering the risk from unintentional movement of plants into the UK, as long as shippers and recipients of plants are aware of the organism.

Pine processionary moth - egg massSpread by egg masses (pictured) being moved on plants for planting is considered to be a low risk, because pine trees are not usually imported and planted in the summer months, when adult moths lay their eggs, and the larvae will have emerged from the eggs before winter, when most pine plants are shipped and planted. Adult females are short lived and unlikely to remain with planting material being moved.

 

Pine processionary moth - pupaAlthough thought to be a low risk, pupae (right) could be brought into the UK in the soil of pine or other host plants for planting, or with any plants which have been growing in the vicinity of infested host plants before export. Inspection is unlikely to detect pupae, which can remain in the soil for up to three years before the larvae emerge. This is the pathway by which it is believed that PPM was moved to the Paris area.

There are currently no requirements for imported plants to be free of this pest. Plants for planting of many species enter the UK every year, but the volume of imports of host plants (or other plant species growing in their vicinity) with soil from areas where PPM is present is not likely to be large. The UK only imported PPM hosts (cluster pine / P. pinaster, hybrid larch / Larix x eurolepis and Scots pine/Pinus sylvestris) in containers from countries in which pine processionary moth is present on six occasions between 2003 and 2012. This is a key area of uncertainty, and additional data are being sought.

b. Natural Spread
Adults of both sexes can fly, and natural dispersal depends on the flight capacity of female moths, which is lower than that of males. Average female flying distance is 1.7km, with a maximum recorded of 10.5km. This is consistent with the rate of spread recorded in the south of the Paris Basin, which has been reported as 5.6km per year. Based on the moth's current known distribution, the risk of natural spread into the UK is still low compared to movement with plants for planting. However, its increasing northwards movement within the rest of Europe does increase the chance of natural spread to the UK.

Susceptible trees

Pine trees (trees of the Pinus genus) are most susceptible to attack, with the following species being particularly susceptible: Austrian pine (Pinus nigra), Aleppo pine (P. halepensis), Canary Island pine (P. canariensis), lodgepole pine (P. contorta), maritime pine (P. pinaster), Monterey or radiata pine (P. radiata), Scots pine (P. sylvestris) and stone pine (P. pinea). Other recorded hosts include the Atlas cedar (Cedrus atlantica) and European larch (Larix decidua).

Among these species, European larch, Scots pine and lodgepole pine are widely grown in the UK, although all are present. Scots pine is our only native pine.

Symptoms

Pine processionary moth - damageDefoliation of needles (right) is the main symptom of PPM attack displayed by the tree itself. Complete defoliation of needles can occur where there is a high level of infestation. Otherwise the nests formed by the caterpillars in January are the most obvious signs of the moth being present. Caterpillars feed at night during the winter, when fewer people are visiting woodlands.

Life-cycle

The life-cycle of PPM is different from OPM's. PPM caterpillars overwinter in tent-like nests high in pine trees, and form processions on the ground in early spring before pupating in the soil until late summer, when they emerge as adult moths. This pupal stage can, however, remain dormant, extending the life cycle over two years.

The adult moths live for only about a day in the summer, during which time they mate and lay eggs in pine trees.

PPM larvae, or caterpillars, hatch in autumn from the eggs laid in the summer, and begin feeding on the trees' needles in autumn.

Identification

Pine processionary mothCaterpillars: The easiest stage of the lifecycle to recognise is the larva, or caterpillar, which is hairy and coloured orange-brown with blue bands. Like its close relative the oak processionary moth (OPM), the larvae move about in nose-to-tail processions. 

However:

  • OPM caterpillars often form a wedge-shaped procession, with one leader and subsequent rows containing several larvae;
  • PPM caterpillars are more likely to form a single line of nose-to-tail larvae;
  • OPM caterpillars are most likely to be found in oak trees;
  • PPM caterpillars are most likely to be found in pine trees;
  • OPM make their nests on the trunks and larger branches of oak trees;
  • PPM make their nests among the foliage (needles) and small branches of pine trees;
  • OPM caterpillars have very long, white hairs which contrast markedly with other, shorter hairs;
  • PPM caterpillars are covered with dense clumps of hairs with less variation in length;
  • OPM catepillars are most likely to be seen in summer; and
  • PPM caterpillars are most likely to be seen in winter and early spring

Pine processionary moth - adultMoths: Adult PPM moths have cream forewings with brown markings, and white hindwings, but to an untrained observer they are difficult to distinguish from other species of moth. They are flying about May to July, and individuals live for only about a day, during which time they must find a mate and lay their eggs in the foliage of a pine or other host tree.

Pine processionary moth - winter nest in a cold areaNests: About January the caterpillars build distinctive, tent-like nests of white, silken, webbing up to the size of a football in the branches and foliage of pine trees, and there can be several nests in a single tree. The caterpillars spend the days in these nests, and leave them at night to forage on the trees' needles.

 

 

Pine processionary mothThe nests can become damaged and discoloured over time (right).

 

 


 

Health precautions

In affected areas take some simple precautions to help minimise the health risks to you and your pets and livestock:

DO NOT:

  • touch or approach nests or caterpillars
  • let children touch or approach nests or caterpillars
  • let animals touch or approach nests or caterpillars
  • try removing nests or caterpillars yourself.

DO:

  • teach children not to touch or approach the nests or caterpillars;
  • train or restrain pets from touching or approaching them;
  • keep horses and livestock away from infested trees - covering or stabling them can help;
  • see a pharmacist for relief from skin or eye irritations after possible PPM contact;
  • call NHS111 or see a doctor if you think you or someone in your care  has had a serious allergic reaction;
  • see a vet if you think your pet or livestock has been seriously affected;
  • call in a pest control expert to remove infestations in your own trees; and
  • report sightings to your Council, or directly to us with Tree Alert.

Further health advice is available from the NHS Choices website.

Outbreak management

Should the pest be found to have entered the UK, the first response would be to try to eradicate the outbreak to prevent establishment. Using emergency powers available to us, we would issue Statutory Plant Health Notices to affected tree owners requiring them to have the infestations removed. Possible treatment options include pesticide applications during the larval stage of the lifecycle, and manual removal of nests and caterpillars by trained operators. For full details of our proposed response to an outbreak, please see our

Action

The UK was given Protected Zone (PZ) status for pine processionary moth in 2017, providing additional protection against the risk of its being accidentally introduced in trade. This means that all imports of pine plants must be accompanied by a plant passport, which certifies that the plants have been grown in a PPM-free place of production (such as a nursery and its surrounding area), a PPM-free area or a PPM-free country.

An additional protection which was already in place was the requirement to pre-notify pending landings of pine plants to the UK plant health authorities, to enable inspection.

Previously, a Rapid Pest Risk Assessment (RPRA) was undertaken by the Food & Environment Research Agency (Fera). This document provides a rapid assessment of the risks posed by the pest to the UK's pine and other host trees, and will help risk managers decide on a response to that threat. It is not a detailed Pest Risk Analysis (PRA), but includes an assessment of whether one should be developed. The recommendation, given the similarity in climate between northern France and coastal areas of southern England, is that a detailed PRA is required to assess the risk of establishment and the associated uncertainties.

In the meantime, statutory action will be taken on findings on a
precautionary basis, in response to the potential risk to the south of England. (See 'Outbreak Management' above). 

Reporting sightings

Tree Alert iconIf you think you have spotted signs of pine processionary moth please tell us using our Tree Alert form

The pest is most likely to be found in pine trees. It can be confused with its close relative, the oak processionary moth, which, as its name implies, is most likely to be found in oak trees. Both species should be reported using the Tree Alert form. Note that Tree Alert requires a well-lit digital photograph to be uploaded, which greatly helps our analysis.

Research

Publications/Further reading

  • EPPO diagnostic protocol for Thaumetopoea pityocampa

  • Our Pest Alert can be printed and used as a poster or leaflet to raise awareness among relevant groups, such as nursery and garden centre staff.

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Last updated: 22nd August 2017