**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THIS PROJECT SEEKS TO UNDERSTAND WHERE POLLINATORS AND POLLINATION SERVICES ARE MOST AT RISK FROM CLIMATIC VARIABILITY. WE WILL ACCOMPLISH THIS GOAL BY LINKING PHYSIOLOGICAL RESPONSES TO CLIMATE, TO POLLINATOR HEALTH AND POLLINATION ACROSS 100 SITES IN 10 US CITIES THAT COVER 6 STATES AND 12 USDA CLIMATE ZONES. IN EACH BACKGROUND CLIMATE, URBANIZATION ITSELF CREATES MICROCLIMATES THAT VARY IN TEMPERATURE AND MOISTURE, ALLOWING ASSESSMENT OF POLLINATOR PERFORMANCE UNDER A WIDE RANGE OF CLIMATE CONDITIONS BOTH IN AND OUTSIDE OF CITIES. WORKING WITH SEVERAL COMMON TAXA, OUR OBJECTIVES ARE TO: 1) ASSESS BEE VULNERABILITY TO WARMING AND DROUGHT ACROSS A RANGE OF TAXA AND BACKGROUND CLIMATES, 2) DOCUMENT CONSEQUENCES OF WARMING AND DROUGHT FOR POLLINATOR HEALTH AND ABUNDANCE, AND 3) LINK CHANGES IN POLLINATOR PHYSIOLOGY, HEALTH, AND ABUNDANCE TO POLLINATION SERVICES. THESE OBJECTIVES WILL BE ACCOMPLISHED BY: 1) MEASURING PHYSIOLOGICAL TOLERANCE TO WARMING AND DEHYDRATION, AS WELL AS BODY TEMPERATURES AND WATER CONTENTS OF FORAGING BEES, 2) MEASURING POLLINATOR HEALTH (LIPID AND GLYCOGEN STORES) AND ABUNDANCE, AND 3) MEASURING POLLEN DEPOSITION IN A MODEL CROP. COMBINED, THESE APPROACHES WILL IDENTIFY WHICH POLLINATOR SPECIES ARE MOST AT RISK OF HEAT AND DROUGHT STRESS, AND WHICH REGIONS OF THE US COULD SUFFER GREATEST CLIMATE-RELATED LOSS OF POLLINATORS AND POLLINATION SERVICE. THESE RESULTS WOULD PROVIDE THE FIRST MECHANISTIC ASSESSMENT OF HOW TEMPERATURE AND WATER BALANCE INFLUENCE BEE HEALTH, POPULATION SIZES, AND POLLINATION SERVICES ACROSS THE US. THUS, THE DESCRIBED RESEARCH WILL ADDRESS THIS RFA BY HELPING UNDERSTAND RISKS TO POLLINATOR HEALTH.