Time course study of Bactrocera oleae (Diptera: Tephritidae) pupae predation in soil: the effect of landscape structure and soil condition

Environmentally friendly control measures are necessary for the olive fruit fly Bactrocera oleae (Rossi). Predation of pupae in soil should be better understood because it contributes to the natural control of pest populations. A time course field trial was carried out in 2015 and 2016 in 15 olive orchards selected to represent a gradient of landscape complexity. Exclusion cages were used to estimate predation rate. A combination of tillage intensity and soil coverage by herbaceous vegetation, hereafter referred to as soil condition, was also assessed as a factor affecting predation rate. The viability of the pupae recovered from the field was also evaluated. Predation was higher in the autumn than in late winter-early spring, although predation rate values were generally quite low. Landscape structure affected predation. In the autumn, the area of Mediterranean scrublands promoted predation in the olive groves. In late winter-early spring, weak tendencies were registered. Soil condition affected predation in autumn as well. The intense tillage and poor soil coverage were related to lower values of predation rate. To favour conservation biological control of B. oleae by pupae predation, it is advisable to reduce the intensity of soil management, especially in autumn, and to preserve areas of scrublands surrounding the olive groves.