Landscape effects on the complex of Bactrocera oleae parasitoids and implications for conservation biological control

We studied the parasitoid complex of Bactrocera oleae Rossi (Diptera: Tephritidae) in order to analyse the parasitism response to landscape structure at different spatial extents. Olive fruits were sampled and incubated in the laboratory for insect emergence, thus allowing the calculation of parasitoid emergence rates. A landscape analysis was performed in five concentric buffers, ranging from 0.5 to 2 km diameter around the sampling points. Woodland was chosen as focal class. The percentage of landscape and the splitting index, a measure of fragmentation, were used to quantify landscape composition and configuration, respectively. Significant effects of landscape on parasitism rates were detected. In particular, the percent parasitoid emergence was negatively affected by the splitting index of woodland at a spatial extent ranging from 1 to 2 km. These findings suggest that landscape characteristics are likely to affect parasitoids in well-structured agroecosystems as well. In particular, connectivity at a large scale may favour B. oleae parasitoids more than the abundance of woodland. Potential implications for conservation biological control are discussed.