GEOGRAPHICAL AND HISTORICAL VARIABILITY IN POPULATION PATTERNS AND LIFE SYSTEMS OF THE LARCH SAWFLY (HYMENOPTERA: TENTHREDINIDAE)

Abstract

The larch sawfly, Pristiphora erichsonii (Hartig), has exhibited several distinctive population patterns in different parts of its Holarctic distribution and during different periods of time in some geographic areas. These patterns include a latent type, where the larch sawfly is never a pest, a permanent type, which causes severe damage, and several temporary types characterized by periodic outbreaks. The different population patterns are associated with differences in the life systems of the populations: the stable latent type with a diverse environment and a rich parasite complex; the stable permanent type with an impoverished parasite complex, interactions with food availability and no effective specific parasites; and the temporary type with an intermediate parasite complex which includes one very effective specific larval parasite. Thus, population stability is related to either maximal or minimal diversity in numbers of parasite species and instability to intermediate levels. The comparison of population patterns and life systems provides a guide to the development of biological control programs.