The impact of landscape composition on the occurrence of a canopy dwelling spider depends on orchard management
Résumé
Enhancing naturally occurring generalist predators can improve pest control. In orchards, canopy-dwelling species are major actors of pest control because pests attack fruits and growing shoots within the canopy. Cheiracanthium mildei, an arboreal spider, is a predator of several important insect pests. We assessed its autumnal occurrence in a set of 61 commercial apple orchards over three consecutive years (2010-2012). We determined the impact of agronomic and land-cover characteristics on C mildei occurrence at both the local and landscape levels using a random forest analysis and regression trees. This approach highlighted the differential effect of landscape variables according to local orchard pest management. First, the presence of exclusion nets against the codling moth (Cydia pomonella) increased C. mildei occurrence by 59%. Second, landscape variables only influenced C mildei occurrence in orchards that were not covered by nets. In particular, abandoned orchards increased C mildei occurrence in orchards not covered by nets and not surrounded by organic orchards. Third, overall, habitats containing trees increased C. mildei abundance in orchards with and without nets, which is consistent with the arboreal habitat of this species. Lastly, the occurrences of C. mildei and of C. pomonella were not related, indicating that the enhancement of C. mildei does not preclude a control of this major pest