Abstract
We have monitored the population densities of the autumnal moth at two localities in the Abisko valleys for two periods: 1955-1967 and 1984-2003. The regrowth of the polycormous mountain birch forest has been described after a severe outbreak that killed most mature stems in 1954-1955. The rate of parasitism of larvae and pupae has also been estimated. Last year outbreak densities occurred at several sites along Lake Torneträsk and the densities in the Abisko valley reached the highest peak since 1965 (30% defoliation). The rate of larval parasitism was very low last year and the winter has been mild, all indicateing that we will have high densities or even increasing densities this summer. Previous analyses show that parasitoids is an important mortality factor contributing to drive the cyclic fluctuation pattern by a delayed density dependent parasitism suppressing declining densities of moths to very low numbers. The project has no financial support this year but it seems to be important to follow the development of the populations of moths and parasitoids over the current population peak.
Sweden