| Summary: | <i>Nosema ceranae </i>is a microsporidian fungus that parasitizes the midgut epithelial cells of honey bees, <i>Apis mellifera</i>. Due to the role that midgut microorganisms play in bee health and immunity, food supplementation with prebiotics and probiotics may assist in the control of <i>N. ceranae</i>. The dietary fiber prebiotics acacia gum, inulin, and fructooligosaccharides, as well as the commercial probiotics Vetafarm Probotic, Protexin Concentrate single-strain (<i>Enterococcus faecium</i>), and Protexin Concentrate multi-strain (<i>Lactobacillus acidophilus</i>, <i>L. plantarum</i>, <i>L. rhamnosus</i>, <i>L. delbrueckii</i>, <i>Bifidobacterium bifidum</i>, <i>Streptococcus salivarius</i>, and <i>E. faecium</i>) were tested for their effect on <i>N. ceranae</i> spore loads and honey bee survivorship. Bees kept in cages were inoculated with <i>N. ceranae</i> spores and single-dose treatments were administered in sugar syrup. Acacia gum caused the greatest reduction in <i>N. ceranae</i> spore numbers (67%) but also significantly increased bee mortality (62.2%). However, Protexin Concentrate single-strain gave similarly reduced spore numbers (59%) without affecting the mortality. In a second experiment, multiple doses of the probiotics revealed significantly reduced spore numbers with 2.50 mg/mL Vetafarm Probotic, and 0.25, 1.25, and 2.50 mg/mL Protexin Concentrate single-strain. Mortality was also significantly reduced with 1.25 mg/mL Protexin Concentrate single-strain. <i>N. ceranae</i>-inoculated bees fed 3.75 mg/mL Vetafarm Probotic had higher survival than <i>N. ceranae</i>-inoculated bees, which was similar to that of non-inoculated bees, while <i>N. ceranae</i>-inoculated bees fed 2.50 mg/mL Protexin Concentrate single-strain, had significantly higher survival than both <i>N. ceranae</i>-inoculated and non-inoculated bees. Protexin Concentrate single-strain is promising as it can reduce <i>N. ceranae</i> proliferation and increase bee survivorship of infected bees, even compared to healthy, non-infected bees.
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