Parasitering på en expanderande art : har kartfjärilen undkommit sina naturliga fiender?

Abstract: Warmer climate is a driving factor to species expansion northwards. Expansion to new areas can result in escape from natural enemies, resulting in reduced levels of mortality and thereby potentially increasing the rate of expansion. The most important parasitoid species attacking butterfly larvae belong to the families Tachinidae, Ichneumonidae and Braconidae. The aim of this thesis was to investigate parasitism and difference between populations in established area and newly colonized area for the European map butterfly, Araschnia levana, in order to examine if the butterfly has escaped from some natural enemies. In 1982 the first European map butterfly was observed in Sweden and has now established up to middle Småland. In order to see if the European map butterfly has escaped from natural enemies in newly colonized areas reared groups of larvae from the first generation where placed in the different areas (from Skåne up to the south of Småland). Larvae where collected after a time in the field and reared until they became adults. No parasitoids were hatched from any of the larval groups, and hence, there was no indication of lower parasitism in newly colonized area. One explanation for this can be that the European map butterfly has been established for a short time in Sweden and therefore can the whole range in Sweden be regarded as a newly colonized area. The method that was used in order to find parasitoids can also have influenced the result. The European map butterfly can despite this result have left their enemies behind when expanding northwards in Sweden.