STUDIES ON THE POPULATION-DYNAMICS OF THE BARK BEETLE LEPERISINUS-VARIUS (FABR) (COL, SCOLYTIDAE) ON EUROPEAN OLIVE (OLEA-EUROPAEA)

Within-generation mortality of the bark beetle L. varius was studied in a Spanish olive orchard by placing cut logs in the field for adult females to breed. Mortality was greatest at the larval stage with only 10 % of the original egg number surviving to adulthood. There was no evidence that the density of eggs laid per maternal gallery affects subsequent mortality at the egg, larval or pupal stages. The density of maternal galleries on a log, however, was found to have a positive influence on the mortality of larvae, but not of eggs or pupae. Part of this density-dependent mortality could be attributed to insect parasitoids, but the effects of intraspecific competition between larvae was also important. However, the relative contribution of each of these components to the density-dependent relationship was unclear. A simple model showed that the population is regulated by density-dependent larval mortality at an eqiulibrium of 11 newly-emerged females/dm2. Overwintering adult mortality is unlikely to affect this equilibrium significantly. However, year-to-year variations in density-independent egg mortality (or oviposition success) was shown by the model to have a major potential effect on both the equilibrium level and population stability.