Contents

• Main Authors: Elnar Olofsson, Studia Forestalia Suecica
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Distribution; life history; fecundity; mortality; damage; Pinus sylvestris; Pinus contorts; Northern Sweden
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.161.719; http://epsilon.slu.se/studia/SFS193.pdf

During outbreaks, Microdiprion pallipes (Fall.) is the most destructive of the pine sawflies in Sweden. Its distribution includes most provinces, but damaging outbreaks have until recently occurred only in two inland areas in northern Sweden. These areas are characterised by high elevation, a harsh climate, and slow tree growth. The four recorded outbreak periods showed a 10 year periodicity. Outside these areas, a lesser outbreak occurred in 1988 to 1990, on the east coast (province of Uppland). Outbreak patterns, life history variation, and mortality factors were studied. Factors that may explain the distribution of outbreaks and the population patterns were identified. Experimental and observational evidence on the potential of various factors to influence fecundity, dispersal, and survival was evaluated. In the outbreak areas, there were few major population factors. Parasitism by Rhorus substitutor (Thunb.) was the largest cause of larval mortality and the only important densitydependent mortality factor. The different diapause strategies of M. pallipes and R. substitutor may contribute to stabilise this system. Different flight periods of the host and the parasitoid may explain a