Organic farming positively affects honeybee colonies in a flower-poor period in agricultural landscapes.
Conventional farming has been implicated in global biodiversity and pollinator declines and organic farming is often regarded as a more ecological alternative. However, the effects of organic farming on honeybees remain elusive, despite honeybees' importance as pollinators of crops and wild plants. Using 6 years of data from a large-scale study with fortnightly measurements of honeybee colony performance traits (10 apiaries per year distributed across a 435 km2-large research site in France), we related worker brood area, number of adult bees and honey reserves to the proportions of organic farmland in the surroundings of the hives at two spatial scales (300 m and 1,500 m). We found evidence that, at the local scale, organic farming increased both worker brood production and number of adult bees in the period of flower scarcity between the blooms of oilseed rape and sunflower (hereafter 'dearth period'). At the landscape scale, organic farming increased honey reserves during the dearth period and at the beginning of the sunflower bloom. The results suggest that worker brood development benefitted from organic farming mostly through a more diverse diet due to an increase in the availability of diverse pollen sources in close proximity of their hives. Reduced pesticide drift may have additionally improved bee survival. Honey reserves were possibly mostly affected by increased availability of melliferous flowers in foraging distance. Synthesis and applications. Organic farming increases honeybee colony performance in a period of resource scarcity, likely through a continuous supply of floral resources including weeds, cover crops and semi-natural elements. We demonstrate how worker brood area increases in the critical dearth period (between the blooms of oilseed rape and sunflower). This has previously been linked to winter colony survival, suggesting that organic farmland may mitigate repercussions of intensive farming on colony vitality. We conclude that organic farming benefits a crucial crop pollinator with potential positive implications for agriculture in the wider landscape.