Microalgae functional feed additives strengthen immunity and increase longevity in honey bees

Honey bees (Apis mellifera) are faced with a myriad of immunological threats, often worsened by poor nutrition. The use of functional feed additives offers a promising strategy to address colony nutritional deficiencies while helping strengthen bee immune responses and mitigate stress. Microalgae have gained recognition as beneficial diet ingredients for livestock due to their abundance of essential nutrients and immunomodulatory properties. Here, we tested the effects of microalgae-containing feed on honey bee immunity, lifespan, and nutrient assimilation. Caged bees were fed a commercial artificial diet or the same diet with added pollen, spirulina (Arthrospira platensis) or Chlorella (Chlorella vulgaris). Immune-related gene expression, longevity, and body weight were measured following six days of ad libitum feeding. All diets resulted in similar body weights, indicating adequate nutrient assimilation. While bees fed the pollen-containing diet lived the longest (median lifespan = 51 days), bees fed spirulina- and Chlorella-containing diets lived significantly longer (median lifespan = 48 and 46 days, respectively) than those fed the base diet (median lifespan = 40 days). Spirulina-fed bees exhibited significantly higher expression of several antimicrobial peptide (AMP) genes relative to the base diet and had superior bacterial clearing ability after injection with live E. coli cells. We propose that this increased immunocompetence is at least partially due to elevated AMP levels. Our findings suggest that the tested microalgae can improve honey bee longevity and immune functions with negligible health costs relative to a commonly used artificial diet. Determining the effects of microalgae feed additives in field-relevant contexts and in the face of diverse pathogen challenges should be the focus of future research efforts.