Efficacy of a Microalgal Feed Additive in Commercial Honey Bee Colonies Used for Crop Pollination

Honeybees are experiencing nutritional deficienciesrelated tointensive agriculture and climate change, posing major threats tothe ecosystem services they provide. Colonies managed for crop pollinationare fed artificial diets to offset reduced pollen in the environmentand to stimulate population growth. Here, we evaluated the effectsof a spirulina microalga feed additive on commercial honey bee coloniesin an agriculturally intensive desert environment. One hundred honeybee colonies were used in a randomized block design that was replicatedat two apiary sites over 4 months leading up to spring almond pollination.Colonies were fed a pollen-free artificial diet or the same diet containing25% spirulina. Unfed colonies were randomly assigned within treatmentblocks as controls. We measured colony population size, brood production,thermoregulation, and a panel of molecular biomarkers associated withnutritional status, stress responses, and gut microbiota. Hive broodimaging and continuous temperature data enabled sensitive detectionof diet treatment effects. Spirulina feed significantly improved broodproduction and thermoregulation prior to almond pollination relativeto unfed controls. Bees fed spirulina had distinct expression profilesof nutrition and stress response genes, but gene expression was primarilydriven by the apiary site. We conclude that spirulina is a sustainablefeed additive with potential to improve crop pollination efficiencyby supporting larger, healthier honey bee colonies.