Key factors and regulation of population of Saissetia oleae (Hom., Coccidae) on olive trees in the region of Magnesia, Greece

Population studies of Saissetia oleae Olivier were carried out in the regio n of Magnesia (eastern central Greece) in a heavily infested olive orchard for five consecutive generations (1988/89-1992/93). The aim of the study wa s to investigate the causes of the outbreak and to evaluate the role of nat ural enemies on the population dynamics of S. oleae. The performed analysis on the constructed life-tables indicated that mortality of crawlers and mo rtality during autumn and spring, comprising the action of internal parasit oids (mainly Metaphycus helvolus) and predators (mainly coccinelids), were the main key factors that determined the population changes of S. oleae dur ing the course of the study. Mortalities during autumn and spring were rela ted to population density, with direct density-dependent relationships indi cating that these mortalities acted both as key factors and regulating mech anisms. The regulating action was probably due to M. helvolus because the e stimates of parasitism during the same periods were also related to populat ion density with the same type of relationship. It was concluded that the o utbreak was caused by the reduced action of natural enemies, presumably due to pesticide treatments applied against other olive pests the previous yea rs. However, when their population recovered, they suppressed the pest popu lation again. Therefore, preservation of natural enemies by applying select ive control methods against the other olive pests is essential.