Recent large-scale surveys indicate existence of a breeding population in Scotland
News from Forest Research: November 2009
Pine-tree lappet moth caterpillars, Dendrolimus pini, are major defoliators of Scots pine forests in Europe. Adult male moths of this species have only been recorded in Britain as rare migrants but since 2004 they have been captured in increasing numbers near Inverness.
Concerns about the presence of male pine-tree lappet moths prompted large-scale surveys to be carried out near Inverness by Forest Research (FR), Forestry Commission Plant Health Service, Forest Enterprise Scotland and Butterfly Conservation. The surveys aimed to determine whether the moth is established and breeding, and the extent of its distribution in Scotland. The former is indicated by the presence of eggs, caterpillars and/or pupae; the latter is shown by the distribution of the much more mobile moths captured by pheromone and light traps.
In June, 282 pheromone traps were set up at 47 Forestry Commission and private woodland sites, mostly within 20 km of the suspected centre of population, near Kiltarlity in Invernessshire. Important pine forests in Culbin, Glen Affric and Inshriach were also monitored.
The pheromone traps caught eight moths at five of the 47 sites. Light traps were also used, and these captured 90 moths from five sites. All 98 moths caught were male and came from seven different sites within 7 km of Kiltarlity. In September, further research was carried out at these seven sites: 1900 sticky bands were attached to tree trunks to catch caterpillars as they descend to hibernate in the soil. In addition, forty-two Scots pine trees were felled and searched for caterpillars, leading to the first discovery of a caterpillar and a pupa cocoon in Scotland. These discoveries confirmed the existence of a breeding population which we believe may have been around since at least 2008.
To determine the origins of the Scottish population of pine-tree lappet moths, FR undertook DNA analysis of 18 Scottish and 6 German specimens. The latter showed higher diversity, with the former showing a narrow genetic base, possibly indicating recent colonisation of Scotland by one or very few individuals.
Further surveys are planned in the near future to look for overwintering caterpillars and adults. In addition, we will undertake climate change modelling to investigate the potential for this species to spread.