Perennial flower strips in apple orchards promote natural enemies in their proximity

Apple production across Europe is experiencing major yield losses due to pest damage, and the need for alternative production methods are growing. Ecological infrastructures are important to create resilient production systems and increase functional biodiversity. This study investigated perennial flower strips as a means of promoting natural enemies, thereby reducing infestation by the rosy apple aphid, Dysaphis plantaginea, and fruit damage caused by it. In 2016 and 2017, effects of perennial flower strips were assessed in eight organic apple orchards with and without flower strips. In orchards with flower strips, assessments were done in tree rows at two distances: 1st and 3rd row from the flower strip. Assessments included field samples of arthropods, visual observations of D. plantaginea symptoms and observations of predators, observations of predators directly associated with aphid colonies, and fruit damage. In 2016, significantly more symptoms of D. plantaginea were observed in the 3rd row from the flower strip compared to the 1st row from the flower strip. Both years, more predators were observed in the 1st row from the flower strip than in the 3rd row from the flower strip. In 2017, more predators were observed in orchards with a flower strip than in orchards with no flower strip, and more predators were observed inside the aphid colonies in trees in the 1st row from the flower strip than in the 3rd row from the flower strip. Predator diversity in apple trees was also positively affected by proximity to a flower strip. In conclusion, perennial flower strips consistently promote the occurrence of natural enemies in their proximity, while the effect decreases with distance. The correlation between aphid abundance and predators was not always consistent, likely because the majority of the observed predators were generalists and therefore contributing to the natural regulation of the entire herbivore complex in the apple orchards.