POLLINATORS PROVIDE BILLIONS OF DOLLARS IN CROP POLLINATION ANNUALLY, AND PATHOGENS HAVE BEEN IMPLICATED IN BEE DECLINES. NUTRITION AND DIET ARE IMPORTANT FACTORS IN BEE HEALTH AND PATHOGEN RESISTANCE. WE DISCOVERED THAT SUNFLOWER POLLEN DRAMATICALLY REDUCED CRITHIDIA INFECTION IN BUMBLE BEES AND NOSEMA INFECTION IN HONEY BEES, PROVIDING INNOVATIVE OPTIONS FOR IMPROVING BEE HEALTH VIA POLLEN SUPPLEMENTS AND PLANTINGS. HOWEVER, WE DO NOT KNOW HOW SUNFLOWER POLLEN REDUCES BEE PATHOGENS. HERE, WE FOCUS ON CRITHIDIA INFECTION IN BUMBLE BEES AS A MODEL SYSTEM TO UNDERSTAND MECHANISMS UNDERLYING EFFECTS OF SUNFLOWER POLLEN, USING LABORATORY EXPERIMENTS TO EVALUATE MULTIPLE, NON-MUTUALLY EXCLUSIVE MECHANISMS. IN OBJECTIVE 1, WE WILL ASSESS HOW SUNFLOWER POLLEN TRAITS DRIVE EFFECTS, INCLUDING POLLEN CHEMISTRY, NUTRITION, AND MORPHOLOGY. IN OBJECTIVE 2, WE WILL INVESTIGATE MECHANISMS ASSOCIATED WITH HOW BEES RESPOND TO SUNFLOWER POLLEN, INCLUDING CHANGES IN GUT TRANSIT TIME, GENE EXPRESSION, IMMUNE FUNCTION, AND THE GUT MICROBIOME. OUR PROPOSAL ADDRESSES THE MAIN PROGRAM PRIORITY TO "SUPPORT BASIC AND APPLIED RESEARCH TO PROMOTE HEALTHY POPULATIONS OF ANIMAL POLLINATORS" AS WELL AS THE PRIORITY TO "DEVELOP AND EVALUATE INNOVATIVE TOOLS, STRATEGIES OR TECHNOLOGIES TO FACILITATE EFFORTS TO INCREASE POLLINATOR HEALTH." DISCOVERING THE MECHANISM BY WHICH A SIMPLE CHANGE IN DIET CAN SO EFFECTIVELY REDUCE DISEASE WILL ACCELERATE TRANSLATION OF OUR DISCOVERY INTO APPLICATIONS MEDIATING BEE HEALTH AND BREEDING PROGRAMS FOR UNDERLYING FLORAL TRAITS. GIVEN THE AGRICULTURAL VALUE OF POLLINATORS, UNDERSTANDING THE MECHANISMS DRIVING THE EFFECTS OF DIET QUALITY ON BEE HEALTH IS A KEY COMPONENT OF EFFECTIVE MANAGEMENT STRATEGIES.