The pine tree lappet moth (Dendrolimus pini) is a native of continental Europe, Russia and Asia, where it causes periodic, large-scale damage to pine plantations. This damage sometimes covers thousands of hectares, with outbreaks lasting up to eight years in some parts of its range. Outbreaks and resultant defoliation by pine tree lappet moth caterpillars can impair tree growth and tree health, making trees more susceptible to other organisms such as bark beetles and wood-boring insects, the effects of which could ultimately lead to tree deaths. This could lead to significant ecological, economic and, ultimately, social impacts.
In Scotland, adult male moths were first caught in 2004 in a pine plantation to the west of Inverness, and then in the river Beauly catchment, but the presence of this moth was not reported to the Forestry Commission until 2008.
An Outbreak Management Team was therefore set up by the Forestry Commission in late 2008 to manage the potential threat posed by the pine tree lappet moth. A contingency plan was put in place, a key part of which was introducing immediate controls on the movement of timber from the outbreak area.
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.
Initial controls restricted timber and foliage movements in the moth’s 'active period' (1 March to 30 November). During this period only bark-free timber could be moved outside the outbreak area. These initial controls allowed time to determine whether a breeding population was present, (the capture of caterpillars in September 2009 confirmed that there was) and to investigate the life cycle, origin and likely impact of this moth.
A programme of regular monitoring shows that the population density is currently low and the moth remains confined to a small part of the Beauly catchment.
Map (PDF 2.4MB) of the contrrol area.
Based on a combination of current evidence and expert advice, the OMT considered that the level of timber movement controls should be reduced so that woodland owners could resume active management of their forests. Such active management activities will help to maintain the health and resilience of forests to the wide variety of insect pests and tree diseases found in the natural environment.
However, through the OMT we will continue to work closely with Butterfly Conservation Scotland, SNH, ConFor and woodland owners to monitor the distribution and population levels of the moth and to ensure management of this potential pest species remains balanced and risk-based.
There are two possible explanations for the recent discovery of this moth in Scotland. It may be part of an overlooked remnant population or, alternatively, its presence represents a more recent introduction of the species which has since become established.
The OMT decided to explore these two alternatives by commissioning a study to compare mitochondrial DNA variation in Scottish moths with that of samples from across its native range.
Results to date indicate that:
- variation in mitochondrial DNA 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. 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; and
- so far an identical ‘match’ for the Scottish DNA sequence has not been found in other parts of Europe, but this is not surprising given the very large range of this species and the impracticality of obtaining samples from every sub-population.
The pine tree lappet moth has not been caught in any of Scotland’s native Caledonian pine forests surveyed to date.
Climate modelling work suggests that summer conditions in the coming decades, especially in the drier east of Scotland, may become more favourable for outbreaks of the moth. However, the potential impact on the moth population of Scotland’s variable autumn and winter climate is not yet known.
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