Larsson et al.: A local outbreak of the Northern Pine Processionary Moth Thaumetopoea pinivora on Gotland, South Sweden A LOCAL OUTBREAK OF THE NORTHERN PINE PROCESSIONARY MOTH THAUMETOPOEA PINIVORA ON GOTLAND, SOUTH SWEDEN

An outbreak of the northern pine processionary moth Thaumetopoea pinivora is currently occurring on Pinus sylvestris in an area of about 3,000 ha at the northern limit of its distribution on the Baltic island of Gotland, south Sweden,. It is not clear how long the population has been present on Gotland, but from observations made by the local residents it appears that it has been present at least since the 1930s. Thaumetopoea pinivora has a two-year development cycle on Gotland, with discrete year classes; high larval densities occur in even years and much lower densities in odd years. The larvae feed between April and July on mature pine needles, and release microscopic hairs that can cause severe allergic reactions in humans. Presumably, the population escaped from controlling factors, but no strong control agent has been identified. A tachinid fly (Blondelia nigripes) is present in the population, but no precise data on degree of parasitism are available