Forestry Commission logo

Pine-tree lappet moth - Questions and Answers

1. What is the distribution of Pine-tree lappet moth abroad?

Its natural range is the Scots pine forests of continental Europe, where it is widespread, occurring in every European country as well as Russia and parts of Asia. It has also been reported in North Africa.

2. Has it ever occurred in Britain before?

There have been occasional sightings of single specimens (on the south coast of England and in the Channel Islands in the mid-20th century, Isle of Wight in August 1996, Guernsey in 1989 and 1997, 2000, 2003, 2004 and five from Jersey between 2003 and 2008, Cornwall in August 2003 and Kent in 2008). These were probably ‘migrant’ males blown across the English Channel.

There is a report that a caterpillar found in Essex in 1999 on a pine tree imported from Italy was bred out to produce a female moth. It was first recorded in Scotland in 2004.

3. Is it possible that this is a native species which has only just been discovered in Scotland?

There is currently no clear evidence to confirm such a theory, but an exact DNA match with any other population has yet to be found. Extensive DNA investigations have been undertaken to see whether we could determine whether this is a small, residual native population, or if it was likely to have been a recent introduction.

Although current DNA evidence (see 16, below) does not rule out the possibility that this could be a previously undiscovered native species, we believe that this is unlikely. 

4. If it is a recent arrival, how did it get here?

We do not know. It could have been brought in on imported pine trees, on forestry machinery from abroad, or with wood products or wood packaging - but it is also possible that it might have been accidentally or deliberately released.

We have no information that would confirm which of these possible routes could have led to the current finds, and it remains most unlikely that we will be able to trace-back unless further DNA testing finds a very close match to an overseas source population.

5. What species of tree do the caterpillars feed on?

Its preferred host is Scots pine (Pinus sylvestris), but it is also known to live and feed on other pine species and, in outbreak conditions, on other coniferous trees such as Sitka spruce, Norway spruce and Douglas fir, all of which are grown commercially in Scotland.

6. What is the likelihood that it will continue to survive in Scotland?

High - but it is, as yet, uncertain whether the population will thrive. Initial climate modelling work suggests that the summer climate in this part of Scotland is likely to become more conducive to outbreak conditions as our climate changes. Its primary host, Scots pine, is plentiful in the drier east of Scotland.

However, the impact on caterpillar survival of Scotland’s unpredictable winter conditions, both now and into the future, is unknown, as is the role of natural parasites and predators. Future monitoring data will help to clarify this.

7. How would it spread?

Mainly by flying, although the female moths are very heavy (with eggs) and therefore do not usually fly further than a few hundred metres. Older caterpillars are able to crawl from tree to tree – but can also crawl as much as several hundred metres to reach new stands of trees.

Eggs, larvae and pupae could also be spread on harvested logs being transported on lorries, or on plants or foliage.

8. What is its lifecycle?

Adult moths emerge from pupae in midsummer and live for 9-10 days, during which time they mate.

The females each deposit up to 250 eggs on twigs, needles and the bark of host trees. These hatch within 16-25 days, and the caterpillars feed on pine needles in the tree canopy until winter frosts begin, when they then move down the trees to over-winter between the litter and soil close to the base of trees.

Pine-tree lappet moth caterpillar eating Scots pine needle. Location: Northern Research Station, Roslin, Midlothian, Scotland.In spring the caterpillars return to the tree crowns and continue feeding until they are large enough to pupate.

The caterpillars moult through several, progressively larger stages, growing to as much as 8.0 cm long. Pupation begins in May and June and lasts for 4-5 weeks. Pupae are formed inside loose, partially transparent cocoons, which can be found in tree crowns, bark crevices and under-storey vegetation.

In laboratory conditions it is possible for development from egg to adult to take place in only 6-7 months. In field conditions under our current climate a two-year cycle is believed to be the norm, but a one-year life-cycle under favourable conditions, and a three-year lif-ecycle under less favourable conditions, cannot be discounted.

In locations where the species is an occasional serious pest it has an annual life-cycle, although other Dendrolimus species in northern latitudes can be significant pests even though they have two- or three-year life cycles.

9. Does it have any natural enemies?

Natural enemies in Europe include several bacteria and fungi (particularly on the over-wintering caterpillars), parasitoids (e.g. parasitic wasps and flies) and predators such as ants and birds, which will feed on or attack the larvae. Bats will catch the adults. A number of species of insects have been reported to prey on the moth. 

Studies are under way to determine whether these natural enemies are controlling populations in Scotland.

10. If necessary could we use any of these natural enemies as a means of controlling pine-tree lappet moth?

Possibly, but we would need to do extensive research to ensure that any organisms, particularly if they were to be introduced to Britain from the continent to control the moth, would not cause damage in their own right. This would be costly and could take several years to complete.

It would also have to be approved by the Advisory Committee on Releases to the Environment under the Wildlife & Countryside Act 1981.

11. What would the economic cost be if the population increases and serious damage is caused to our forests?

This is difficult to predict with any certainty. Some of the tree species at risk - particularly Scots pine and Sitka spruce - are commercially important in Scotland's economy. Scotland's forests are estimated to be worth £670 million a year to the Scottish economy, so any significant damage to these species could have a significant impact.

12. Is there anything the public can do to help?

Sightings and suspect captures should be reported to Forestry Commission Scotland (fcscotland@forestry.gsi.gov.uk), telephone 0131 314 6156. Reports should include as precise a description of the location as possible: a grid reference is ideal.

Photographs of the moth or its larvae, and the surrounding habitat, would also be very helpful.

13. How many have been found?

In September 2009, 1900 sticky bands were attached to tree trunks at the seven sites where adult moths had been captured in light and pheromone traps. Thirty-three caterpillars were caught during the autumn descent, and a further 68 were found under the bands during removal in February 2010.

In spring 2009, sticky banding was repeated in two woods, yielding 63 ascending larvae.

During summer 2010, 176 moths were captured by light and pheromone trapping, an increase in total numbers compared to 2009 (when 98 moths were caught), but a slight drop in catches per light trap (a greater intensity of sampling was carried out). There was only a slight extension in range.

Repeat glue banding in autumn 2010, which included five new sites, captured only three larvae in the autumn descent and 53 at band removal in February 2011. A further 48 caterpillars were caught during the spring ascent in 2011.

During summer 2011, 145 moths were caught in light and pheromone traps, and there was a further suggestion of possible range expansion, with moths being captured at new sites on the periphery of the confirmed breeding area. 

Further monitoring is under way to help determine whether this change in abundance could be a result of biotic or abiotic factors.

In autumn 2011, further glue banding was undertaken which included the 4 new sites where adult moths had been caught that summer (2200 tree bands in total).  42 caterpillars were caught at band removal and a further 34 during the spring ascent of 2012. 

During summer 2012, only 35 moths were caught in light and pheromone traps. It is highly likely that the poor spring and summer weather played a part in the low larval and, especially, adult moth captures, because this was also observed for other moth species in 2012.

14. Where were they found?

At a small number of woodland sites in different ownerships in the Kiltarlity area to the west of Inverness, including the publicly owned Boblainy Forest managed by Forestry Commission Scotland. See the map of moth risk zones (PDF 2.4MB).

15. What do your investigations involve?

Investigations have included:

  • surveys of the litter on the ground to check for the presence of over-wintering larvae (caterpillars);
  • attaching sticky bands to several hundred tree trunks in the affected and neighbouring woods in the spring (to catch larvae returning from the ground to the tree canopy) and in the autumn (to catch larvae descending to the ground to overwinter);
  • pheromone and light traps to capture adult male moths;
  • captive rearing to measure growth rates; and
  • DNA analysis and climate modelling.

16. How does DNA analysis help?

Comparing the DNA of the Scottish population with that of other European countries has helped us to understand the genetic make-up of different geographic populations of this moth. Results to-date indicate that:

  • Variation in mitochondrial DNA from samples across Europe formed three groups which showed a distinct geographic pattern. The Scottish samples belong to one of these groups, the members of which have a broad geographic spread from eastern France to the Mediterranean coast and eastwards as far as Mongolia.

    This is evidence that the Scottish population is most likely to have originated from somewhere within this broad area, because moths from these areas share similar ancestry. 

    This could point to them all, including the Scottish moths, originating from a common refugium during the last Ice Age, from which they have naturally spread, or to the Scottish moths having been ‘jump’ spread from somewhere within this area as a result of human activity.

    We are unable to be more specific because an exact match to the Scottish moth sequence was not found.

    Membership of the other two groups consisted of samples from Spain, western France, Scandinavia and central European countries, and these areas are therefore unlikely to have been the source of founding individuals for the Scottish population.

  • Evidence from nuclear microsatellites indicates that the Scottish population has low genetic diversity compared with mainland Europe, suggesting that the population in Scotland might have gone through a genetic 'bottleneck'.

    This maight either indicate that the population has become isolated and declined to low numbers at some stage after post-glacial colonisation from the south or, alternatively, that the population is the result of a recent introduction based on a small number of individuals.

17. Do we know for sure that this moth is not going to cause future damage to pine forests in the east of Scotland?

No, but we have to take a proportionate and risk-based approach. Currently the population is at very low levels and continues to be monitored.

We also know that the previous timber movement controls would, if maintained, have severely restricted active forest management in this area, resulting in less ‘thinning’ and reduced ‘restructuring’ of current even–aged pine woodlands with relatively little species diversity.

This would not only significantly increase the far greater current threat to forest health in this and adjacent areas from foliar diseases such as Dothistroma needle blight but it would also hinder the longer-term aim of increasing the age and species diversity of woodlands in this area – which is one of the key aims of sustainable forest management and, in itself, likely to offer the greatest ‘protection’ against future pest and disease threats.

18. So what are you going to do?

Guided by the OMT we are going to continue to take a proportionate, risk-based approach to the management of this potentially significant pest and:

  • continue to monitor Pine tree lappet moth populations throughout the Kiltarlity area;
  • set up and monitor pheromone traps at those mills in receipt of timber from the Kiltarlity area;
  • apply timber movement restrictions only to higher risk areas, i.e. where breeding populations have been confirmed (see accompanying map), and only in those months where the risks of transporting egg masses and larval clusters out of the area are greatest (mid-May to the end of August);
  • adopt practical biosecurity measures during timber harvesting operations to reduce the risk of moving Pine tree lappet eggs and larvae outside the area;
  • prepare a contingency plan for aerial pesticide/biological control in the unlikely event that a mass outbreak occurs in the future and such action becomes necessary; and
  • subject to funding availability: continue DNA investigations; monitoring/rearing to determine growth rates and life-cycle in Scotland; and establish what natural parasitoids occur in the Kiltarlity area.

5 September 2013