Meta-Analysis and Experimental Evidence Reveal No Impact of Nosema ceranae Infection on Honeybee Carbohydrate...

Honeybees (Apis mellifera) are indispensable pollinators for ecosystem stability and agricultural productivity. However, they face numerous challenges, including pathogens threatening their survival and ecosystem services. Among these pathogens, Nosema ceranae, a microsporidian parasite, causes significant damage to the intestinal tract and induces energetic imbalances in the organism, posing a major threat to both individual bees and entire colonies. In response to infections, bees often engage in behavioral defenses, such as self-medicating with antimicrobial substances available in their environment. We hypothesized that bees infected with N. ceranae might compensate behaviorally by increasing their carbohydrate consumption. To test this hypothesis, we conducted a meta-analysis of existing studies comparing sugar consumption in healthy and infected bees, complemented by an experimental study. In our experiment, we measured sugar intake and quantified trehalose levels in the hemolymph, a key indicator of energy reserves. Both the meta-analysis and experimental results consistently showed no significant differences in sugar consumption between healthy and infected bees. Similarly, trehalose levels in the hemolymph remained comparable between the two groups. Our findings suggest that the infection caused by N. ceranae does not elicit compensatory feeding behavior in honeybees. Moreover, the meta-analysis revealed significant gaps in current research, particularly a lack of studies focusing on forager bees, which face the highest energetic demands among colony members. Our findings call for future studies on the energetic effects of nosemosis and studies conducted under natural or semi-natural conditions.