Immature hoverflies overwinter in cultivated fields and may significantly control aphid populations in autumn

International audienceThis study was based on broad monitoring of spring emergence of hoverflies and of aphid populationsin two French agro-ecosystems. Its aim was to determine whether hoverflies overwinter in agriculturalfields and/or in field margins at immature stages and to what extent local and large-scale landscapefeatures influence the abundance of immature overwintering individuals and the associated biologicalcontrol. Our results show that the influence of the landscape on the abundance of immature overwin-tering hoverflies varies among trophic groups. Non-aphidophagous species plus some aphidophagousspecies, which occasionally feed on crop aphids, preferentially overwinter in field margins near woodedland. Conversely, aphidophagous species, which mainly feed on crop aphids, preferentially overwinterwithin the fields and are less influenced by semi-natural features. This work also shows a strong negativecorrelation between the abundance of hoverflies that overwinter at immature stages within the fields andthe abundance of aphids in the spring, which suggests a biological control by the hoverflies in autumn.Because they may provide a significant service of biological control, the hoverflies that overwinter withinagricultural fields should be taken in consideration in the management of croplands, through agriculturalpractices for example. The landscape configuration also should be considered in order to maximize thehoverflies community in agricultural landscapes, and to maximize the ecosystem services it provides.This study provides valuable insights on overwintering of hoverflies at pre-imaginal stages in agri-cultural landscapes and on the role of this overwintering strategy in the biological control of aphidpopulations. It shows that a landscape mostly composed of cultivated land can provide significant serviceof biological control if semi-natural features are arranged in a convenient way for natural enemies