Potential of Hedgerows with Aromatic Plants as Reservoirs of Natural Enemies of Pests in Orange Orchards

SIMPLE SUMMARY: The present study examined the ability of four Mediterranean aromatic plant species, i.e., oregano, rosemary, sage, and savory, established in hedgerows in orange orchards to support natural enemies of citrus pests in comparison to margins with bare soil or weed vegetation, which is the commonly used management practice. The impact of the aromatic plant hedgerows on conservation of parasitoid wasps, spiders, and predators of insect pests varied with the aromatic plant species and natural enemy group, i.e., savory plants had a positive effect on the abundance of parasitoids and arachnid predators; sage and oregano flowers favored predatory insects, but sage harbored low numbers of parasitoids compared to the main flowering weed species; rosemary hedgerows served as a most suitable habitat for spiders in comparison to the pre-existing weed cover. The results support the use of the tested aromatic plant species as customized reservoirs for certain groups of beneficial arthropods in orange orchards, considering also the possible incorporation of suitable flowering wild plant species in the weed flora. ABSTRACT: In the present study, the potential of hedgerows from Mediterranean aromatic plant species, i.e., oregano, rosemary, sage, and savory, in orange field margins to function as reservoirs of natural enemies of citrus pests was tested in comparison to the common management practice of bare soil or weed vegetation. Assessments were based on the abundance and diversity of parasitoid wasps, spiders, and insect predators in the field margins and on the orange trees for two growing seasons. Savory plants harbored more parasitoids compared to weed vegetation and the other aromatic plants (savory > organic rosemary > sage > oregano). Weed vegetation hosted more arachnid predators than the aromatic plants in their first year in the orchard, but this was reversed with their full growth in the following year (most abundant on rosemary). Oregano and sage favor insect predators. The similarity of the natural enemy communities on the field margins and on the orange trees increased with time, indicating the insects’ movement from the field margins to the trees. The results support the use of the tested aromatic plant species in conservation practices for targeted groups of beneficial arthropods in orange orchards, also considering the exploitation of suitable wild flowering plants of the weed flora.