**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** HONEY BEES AND OTHER POLLINATORS ARE WELL-DOCUMENTED TO BE EXPERIENCING SERIOUS LOSSES, AND THE CAUSES OF THESE LOSSES REMAIN POORLY UNDERSTOOD. GLOBAL WARMING IS ONGOING, AND IS ONE POSSIBLE CONTRIBUTING CAUSE. CLIMATE CHANGE IS EXPECTED TO BE ACCOMPANIED BY INCREASES IN THE FREQUENCY, INTENSITY AND DURATION OF HEAT WAVES WHICH ARE LIKELY TO POSE BOTH SURVIVAL AND NUTRITIONAL STRESS ON HONEY BEE COLONIES. ONE GOAL OF THIS RESEARCH IS TO PROVIDE THE FIRST QUANTITATIVE ASSESSMENT OF THE EFFECT OF HEAT WAVES ON THE HEALTH OF HONEY BEE COLONIES. THS RESEARCH WILL TAKE PLACE IN DESERT ARIZONA, WHERE HISTORICAL AND INCREASING HIGH TEMPERATURES PROVIDE A NATURAL LABORATORY FOR STUDYING THE EFFECTS OF HEAT ON BEES. USING SMALL, NEWLY DEVELOPED DEVICES FOR LONG-TERM TEMPERATURE MONITORING, WE WILL MEASURE TEMPERATURES IN VARIOUS REGIONS OF HIVES THROUGHOUT THE YEAR, INCLUDING DURING NATURAL HEAT WAVES, AND ASSESS HOW NATURAL VARIATION IN TEMPERATURE AFFECTS COLONY FORAGING AND GROWTH. TO EXPERIMENTALLY TEST THE EFFECT OF HEAT WAVES, WE WILL ENCLOSE SOME HIVES IN TENTS AND EXPOSE THEM TO ELEVATED AIR TEMPERATURES, EXAMINING THE ABILITY OF THE BEES TO REGULATE HIVE TEMPERATURE, AND TESTING HOW HEAT AFFECTS COLONY FORAGING, METABOLISM AND EVAPORATIVE HEAT LOSS. TO RELATE THE EFFECT OF INTERNAL HIVE TEMPERATURES TO COLONY GROWTH, WE WILL REAR HONEY BEE LARVAE AND PUPAE AT TEMPERATURES ASSOCIATED WITH HEAT WAVES, AND TEST FOR EFFECTS ON SURVIVAL AND LONGEVITY.A SECOND POSSIBLE CAUSE OF DECLINES IN POLLINATOR HEALTH IS EXPOSURE TO PESTICIDES. WITH RECENT USDA FUNDING, WE HAVE DEMONSTRATED THAT A COMMONLY USED MITO-TOXIC FUNGICIDE HAS STRONG NEGATIVE EFFECTS ON WORKER HEALTH AND COLONY GROWTH AT FIELD-REALISTIC LEVELS, LIKELY MEDIATED BY IMPAIRMENT OF GUT FUNCTION AND CONSEQUENT NUTRITIONAL STRESS. WE WILL MEASURE THE CONSUMPTION OF NEXT-GENERATION FUNGICIDES IN CALIFORNIA ALMOND FIELDS TO DEFINE EXPOSURE OF HONEY BEES TO THESE CHEMICALS. THEN WE WILL TEST THE EFFECT OF CONSUMPTION OF THESE FUNGICIDES ON THE HEALTH AND LONGEVITY OF WORKER BEES, COLONY GROWTH AND REPRODUCTIVE CAPACITY, GUT FUNCTION AND NUTRITIONAL STRESS, AND LEARNING AND NAVIGATION ABILITY.DECLINES IN POLLINATOR HEALTH ARE LIKELY DUE TO MULTIPLE CAUSES, AND THE INTERACTION BETWEEN VARIOUS STRESSORS ON POLLINATOR HEALTH ARE POORLY UNDERSTOOD. THEREFORE, WE WILL TEST FOR ADDITIVE OR SYNERGISTIC INTERACTIONS BETWEEN WARMING AND FUNGICIDE EXPOSURE. WE WILL MANIPULATE THE THERMAL ENVIRONMENT OF HIVES BY PASSIVE METHODS (VARYING SUN VS. SHADING OF THE HIVES, AND COLOR), WHILE FEEDING HALF OF THE COLONIES WITH FIELD-REALISTIC DOSES OF FUNGICIDES, TO TEST HOW INCREASED TEMPERATURES INTERACT WITH FUNGICIDE CONSUMPTION.