Effect of parasitoid competition, ant exclusion and carbohydrate sources on biological control fo Saissetia oleae on olive trees = Efecto de la competición de los parasitoides, la exclusión de hormigas y las fuentes de hidratos de carbono en el control biológico de Saissetia oleae en olivos

The black scale, Saissetia oleae (Olivier), is considered a secondary pest of olive tree in Portugal, where it is attacked by a complex of natural enemies that control its population. Parasitoids of genus Metaphycus (Hymenoptera: Encyrtidae) and Coccophagus (Hymenoptera: Aphelinidae) are among the main natural enemies. In this thesis, the several aspects of the successful natural biological control of this scale are analyzed in the field and laboratory. In detail, we analyzed: (i) whether the facultative autoparasitoid Coccophagus lycimnia (Walker) can adversely affect the population densities of Metaphycus spp. parasitoids and disrupt the biological control of S. oleae; (ii) the effect of ant-exclusion on the biological control of S. oleae and its parasitoid complex; and (iii) the effect of the carbohydrate sources available in the field (nectar and honeydew) on the survival of parasitoids of both genus. For the development of the first objective, the population densities of the scale, the primary parasitoids of the genus Metaphycus and the autoparasitoid C. lycimnia were recorded for three consecutive seasons in 28 olive groves. The populations of the parasitoids followed opposite patterns. At the end of the life cycle of the S. oleae (May), the number of Metaphycus spp. observed was practically nil whereas the number of C. lycimnia was five times greater than at the beginning of the assay. In September and November, Metaphycus spp. parasitoids parasitized smaller scales than C. lycimnia, demonstrating that Metaphycus spp. parasitoids are superior at exploitative competition. Metaphycus spp. and C. lycimnia sex ratio was similar in September, but in November the sexual proportion of Metaphycus spp. was higher than that of C. lycimnia. The facultative autoparasitoid C. lycimnia tended to lay male eggs on Metaphycus spp. females. The density of S. oleae decreased from September to May, when the ratio S. oleae-C. lycimnia reached 2:1. Altogether, these results demons