The population dynamics of the bark beetle Phloeotribus scarabaeoides (Col, Scolytidae) on European olive (Olea europaea)

The life-stage mortalities of the bark-beetle pest P. scarabaeoides were studied in a Spanish olive orchard by placing cut logs in the held for adult females to breed. Mortality was found to be greatest at the larval stage with about 25% of the original egg number surviving to adulthood. The density of eggs laid per maternal gallery does not appear to affect the degree of subsequent mortality at the egg, larval or pupal stages. However, the density of maternal galleries on a log has a positive (density-dependent) influence on the mortality of larvae, but not of eggs or pupae. The density-dependent larval mortality could be attributed to both insect parasitoids and intraspecific competition, but the relative contribution of each was unclear. The proportion of adult females excavating maternal galleries was also shown experimentally to be density dependent. A simple model, based on the information presented, showed that the population is regulated primarily by density-dependence in the level of female attack, stabilizing the population at three attacking females/dm(2). Mortality of overwintering adults in the trees is unlikely to affect this equilibrium significantly.