INSECTS THAT FEED ON PLANTS HAVE MAJOR IMPACTS ON AGRICULTURE, CAUSING DAMAGE AND DISEASE TO CROP AND RESULTING IN SUBSTANTIAL ECONOMIC AND RESOURCE LOSS FOR FARMERS. INSECTS THAT DAMAGE CROPS COME IN TWO GENERAL TYPES: GENERALISTS - INSECTS THAT FEED ON ALL TYPES OF PLANTS; AND SPECIALISTS - INSECTS THAT FEED ON ONLY ONE PLANT SPECIES. SPECIALIST INSECTS ARE OF PARTICULAR INTEREST BECAUSE THEY ARE SO FOCUSED ON A SINGLE PLANT SPECIES THAT IT IS RARE FOR THEM TO CHANGE (OR HOST-SHIFT) TO A NEW PLANT SPECIES. HOWEVER, PREVIOUS RESEARCH HAS FOUND THAT HOST-SHIFTS DO SOMETIMES OCCUR, AND THAT WHEN THEY DO THEY CAN LEAD TO THE FORMATION OF NEW INSECT SPECIES - NOW SPECIALIZED ON THE NEW HOST PLANT. THE SUNFLOWER MAGGOT FLY, A SPECIALIST FRUIT FLY SPECIES, IS CURRENTLY FOUND ON TWO HOST PLANT SPECIES, THE COMMON SUNFLOWER AND THE JERUSALEM ARTICHOKE (ANOTHER SPECIES OF SUNFLOWER). BOTH OF THESE PLANTS WERE CULTIVATED BY NATIVE AMERICANS AND WERE LIKELY SPREAD AROUND NORTH AMERICA DUE TO PRE-COLONIAL FARMING PRACTICES. IN MY RESEARCH, I WILL TEST WHETHER HISTORICAL AGRICULTURAL PRACTICES IN NORTH AMERICA MAY HAVE INFLUENCED THE MOVEMENT OF THE SUNFLOWER MAGGOT FLY FROM ONE PLANT TO THE OTHER, POSSIBLY RESULTING IN A NEW SPECIALIST CROP PEST SPECIES. BY USING THIS HISTORICAL EXAMPLE OF HOST-SHIFTING, MY PROJECT AIMS TO EXPLORE THE ROLE OF AGRICULTURAL PRACTICES ON THE FORMATION OF NEW SPECIALIST PEST INSECT SPECIES.TO DETERMINE IF AGRICULTURAL PRACTICES HAVE INFLUENCED THE FORMATION OF NEW SPECIES OF THE SUNFLOWER MAGGOT FLY, I NEED TO 1) DETERMINE IF THE FLIES ON THE COMMON SUNFLOWER ARE GENETICALLY DIFFERENT THAN THOSE ON THE JERUSALEM ARTICHOKE AND 2) USE POPULATION GENOMIC METHODS TO RECONSTRUCT THE DIRECTION AND TIMING OF HISTORICAL FLY MOVEMENTS AS THEY SPREAD ACROSS THE U.S. TO DO THIS, I WILLCOLLECT FLIES FROM BOTH PLANT HOSTS SITES ACROSS THE U.S. THEN, I WILL SEQUENCE THE GENOMES OF THESE FLIES AND USE POPULATION GENOMIC METHODS TO EXTRACT INFORMATION ABOUT THEIR RELATIONSHIPS TO ONE ANOTHER AND HISTORICAL GEOGRAPHIC DISTRIBUTION. THE SYNTHESIS OF THIS WORK WILL GENERATE SEVERAL MANUSCRIPTS THAT WILL CONTRIBUTE TO OUR CURRENT UNDERSTANDING OF THESE PROCESSES IN SPECIALIST INSECTS. SEVERAL ELEMENTS OF THIS WORK HAVE THE POSSIBILITY OF BEING RELEVANT TO PEST INSECT PREVENTION AND PREDICTION. FIRST, THERE ARE VERY FEW GENOMES AVAILABLE FOR THIS GROUP OF FLIES, SUCH THAT I WILL CONTRIBUTE VALUABLE RESOURCES FOR FUTURE GENOMIC ANALYSES. SECOND, THE METHODS I WILL USE FOR TRACING THE SPREAD OF FLIES ACROSS THE U.S COULD ASSIST IN FUTURE PREDICTIONS OF THE MOVEMENT OF NOVEL AND INTRODUCED CROP PESTS. FINALLY, THIS EXAMPLE OF A SPECIALIST INSECT SHIFTING AMONG CLOSELY RELATED SUNFLOWER SPECIES COULD INFORM FUTURE PLANNING DECISIONS ABOUT THE RISKS OF BRINGING CROP SPECIES INTO REGIONS, ESPECIALLY THOSE WHERE CLOSE RELATIVE OF THE CROP PLANT ARE FOUND.