Effects of semi-natural habitats on spiders in olive groves and their potential role against Bactrocera oleae (Rossi) (Diptera: Tephritidae)

Abstract: To optimise pest control by naturally occurring predators, it is essential to understand their relationship to environmental factors such as management and the landscape context of crop fields. The aim of this study is to clarify how semi-natural habitats, situated in a radius of 1 km around olive orchards, can support pest control. This study is part of the EU project QuESSA. In olive groves, spiders are the dominant predators in terms of richness and abundance and they could potentially be effective against the olive fruit fly Bactrocera oleae (Rossi) (Diptera: Tephritidae), the olive key pest in Italy and in the Mediterranean basin. During the summer of 2014 we sampled canopy spiders in 18 olive orchards of the Monte Pisano area (central Italy). In addition, their potential preys were sampled using sticky traps. We found 72 species of spiders belonging to 15 families. The dominant species was the sheet web spider Frontinellina frutetorum (C. L. Koch, 1834) (Araneae: Linyphiidae). We did not find a clear landscape effect of semi-natural habitat proportion on the spider community, but a strong effect of management practices: insecticide applications reduced spider abundance and richness. Moreover, the activity of B. oleae correlated negatively with the densities of Linyphiidae, suggesting that web-building spiders contribute to the control of this important pest.