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

Honey bees are experiencing nutritional deficiencies related to intensive agriculture and climate change, posing major threats to the ecosystem services they provide. Colonies managed for crop pollination are fed artificial diets to offset reduced pollen in the environment and to stimulate population growth. Here, we evaluated the effects of a spirulina microalga feed additive on commercial honey bee colonies in an agriculturally intensive desert environment. One hundred honey bee colonies were used in a randomized block design that was replicated at two apiary sites over 4 months leading up to spring almond pollination. Colonies were fed a pollen-free artificial diet or the same diet containing 25% spirulina. Unfed colonies were randomly assigned within treatment blocks as controls. We measured colony population size, brood production, thermoregulation, and a panel of molecular biomarkers associated with nutritional status, stress responses, and gut microbiota. Hive brood imaging and continuous temperature data enabled sensitive detection of diet treatment effects. Spirulina feed significantly improved brood production and thermoregulation prior to almond pollination relative to unfed controls. Bees fed spirulina had distinct expression profiles of nutrition and stress response genes, but gene expression was primarily driven by the apiary site. We conclude that spirulina is a sustainable feed additive with potential to improve crop pollination efficiency by supporting larger, healthier honey bee colonies.