Carabid and staphylinid beetles as natural enemies of Bactrocera oleae: a conservation biological control perspective

How can we conserve and enhance the edaphic communities of natural enemies of Bactrocera oleae (Diptera: Tephritidae) and the biological control service they provide, overcoming conflicts between agriculture and biodiversity? Understanding ecological, social and economic interactions is a major challenge for preserving ecosystem services’ functionality in a historical moment of (agro)biodiversity decline. This PhD thesis aims at unravelling key dynamics in olive orchard agroecosystem among its major pest, the olive fruit fly B. oleae, and edaphic natural enemies of the pest’s pupae. Olive orchard agroecosystem generally benefits from less disturbance and higher structural diversity than annual crop systems. Despite the severe damage inflicted by B. oleae, the pest’s ecology and the heterogeneity of natural predators can, at least theoretically, support the efforts toward conservation biological control as a sustainable approach to biocontrol. Literature on the edaphic predators of B. oleae is scarce and incomplete, but the few available data have suggested carabid and staphylinid beetles as potential natural enemies of the above pest. Firstly, we collected Carabids (Coleoptera: Carabidae) throughout a year to firstly provide a list of species dwelling in olive orchards and woody semi-natural habitats. A trait approach widened the perspective and enabled to provide a list of requirements indicating potential predators of B. oleae pupae. The carabid assemblage of the olive orchard showed potential relevant species and traits for the control of B. oleae, being some predators’ phenologies temporally overlapping within the pest cycle. Eighteen olive orchards were then surveyed to inspect local and landscape variables affecting B. oleae pupae predation rate during autumn in two consecutive years. Organic fields were characterized by a predation rate significantly higher than conventional ones. No landscape effect (distance from the focal field to adjacent semi-natural habitat) was detected, while the semi-natural habitats type was likely to affect the predation rate, being the Mediterranean garigue the semi-natural habitat type that contributed more significantly to predation in the cropped field. Molecular technologies are nowadays greatly contributing to the understanding of “who eats whom”. Pseudoophonus rufipes, a species proved to be active in olive orchard when pest pupae are abundant in the soil, was molecularly tested by means of PCR gut content iv analysis in order to detect B. oleae pupae consumption at different post feeding times. B. oleae mtDNA was detected up to 20 h after pupa ingestion with a high percentage of success, without significant differences among sexes, pair primers and sample types (dissected versus non dissected). PCR gut content analysis was also used to quantify the role of staphylinids (Coleoptera: Staphylinidae) in the predation of B. oleae pupae. 24.58% of the field-collected specimens of Ocypus olens, a species abundant in olive orchard, resulted positive for B. oleae mtDNA, demonstrating that O. olens is a predator of B. oleae, at least during autumn and winter. Both field and laboratory studies gave promising results for the conservation biological control of B. oleae. Conservation efforts for carabids and staphylinids are worthy of pursuit, at both local and landscape level.