** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** UNDERSTANDING THE SPECIALIZED RELATIONSHIPS BETWEEN CROPS AND THEIR INSECT PESTS IS A CRUCIAL COMPONENT OF SUCCESSFUL AGRICULTURAL SYSTEMS. HOWEVER, VARIATION AMONG INSECT POPULATIONS IN TIMING OF BREEDING, MATING BEHAVIOR, AND GENETICS CAN MAKE IT CHALLENGING TO DESIGN EFFECTIVELY TARGETED PEST MANAGEMENT STRATEGIES. TWO MAJOR CAUSES OF VARIATION BETWEEN POPULATIONS ARE DISTANCE AND ADAPTING TO A NEW HOST PLANT. DISTANCE RESTRICTS MOVEMENT OF INDIVIDUALS BETWEEN POPULATIONS AND CAN ALLOW POPULATIONS TO EVOLVE GREATER DIFFERENCES FROM EACH OTHER OVER TIME. ADAPTING TO A NEW HOST PLANT FAVORS INDIVIDUALS THAT REPRODUCE BEST ON THAT HOST, RESULTING IN GREATER DIFFERENCES BETWEEN INSECT POPULATIONS THAT USE A DIFFERENT HOST PLANT. I WILL DETERMINE THE RELATIVE IMPORTANCE OF THESE SOURCES OF VARIATION IN MULTIPLE POPULATIONS OF SEVERAL SPECIES OF A FRUIT-INFESTING FLY THAT USE A VARIETY HOST PLANTS, IS WIDESPREAD ACROSS THE UNITED STATES, AND TARGETS AGRICULTURALLY IMPORTANT CROPS, INCLUDING APPLES AND WALNUTS. I WILL MEASURE VARIATION BETWEEN POPULATIONS AND SPECIES IN (1) THEIR MATING BEHAVIORS AND THE TRAITS IMPORTANT IN MATING, INCLUDING BODY SIZE, (2) THE TIMING OF MATING DURING THE YEAR, AND (3) GENETICS. THE RESULTS OF THIS WORK WILL PROVIDE CRITICAL INSIGHTS INTO VARIABILITY AMONG PEST POPULATIONS CURRENTLY AS WELL AS IDENTIFY CHARACTERISTICS OF POPULATIONS OR SPECIES THAT ARE LIKELY TO EVOLVE GREATER DIFFERENCES IN THE FUTURE AND REQUIRE ADDITIONAL MONITORING FOR SUCCESSFUL PEST MANAGEMENT.