Keep your enemies closer: enhancing biological control through individual movement rules to retain natural enemies inside the field

Abstract. Biological control of pests aims at lowering population levels of pest species by favouring natural enemies, in order to reduce the use of pesticides. The movement behaviour of natural enemies is decisive in the success of biological control: when low habitat quality hinders the diffusion of natural enemies from the border, the density of natural enemies may frequently be heterogeneous inside agricultural plots. We hypothesise that the specific relationship between habitat quality and movement behaviour may allow the improvement of biological control by means of a careful allocation of habitat qualities inside and around the plot. We used three tested individual-based movement models, with different levels of complexity ranging from simple cell-to-cell movements to complex strategies including the sinuosity of the path, boundary crossings, perceptual range, and directional persistence. We used the models to explore how the manipulation of habitat quality may allow significant improvements to the residence time of natural enemies inside the field. We suggest that existing field designs are generally inadequate to retain natural enemies. Mechanistic explanations leading to the highest and lowest residence times are used to draw specific management recommendations.