Effects of local and landscape factors on spiders and olive fruit flies

Abstract

Conservation biological control uses naturally occurring enemies to limit pest populations and to increase agricultural sustainability. The olive is an important perennial crop in Mediterranean countries and there is a high demand for alternative solutions to pesticide applications. As spiders are the most abundant predators in olive trees, they could be effective against the olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), the main pest of this crop. In order to optimise the effectiveness of spiders, it is essential to understand their relationship with environmental factors at both the local and landscape scales. We studied spiders and their potential prey in the canopies of 18 olive orchards in different landscapes of the Monte Pisano (central Italy). The abundance and species richness of spiders as well as the abundance of sheet web spiders were lower in conventional orchards than in organic orchards. The composition of spider communities was affected by the amount of Mediterranean garigue in the surrounding landscape, and the abundance of flies increased with increasing percentage of wood in the landscape. Olive fruit fly densities were negatively correlated with cursorial and sheet web spiders⿿ abundance, suggesting that spiders may be involved in pest suppression. As the response of spiders to local and landscape factors was family and guild specific, tailored management for biological control requires further clarification of the individual and interactive effects of the different spider families and guilds on B. oleae.