SQUASH BUGS (ANASA TRISTIS) ARE SIGNIFICANT PESTS OF SQUASHES AND MELONS IN THEIR OWN RIGHT AND ARE ALSO OF CONCERN BECAUSE OF THEIR ABILITY TO VECTOR A PLANT PATHOGEN, STRAINS OF THE BACTERIUM SERRATIA MARCESCENS THAT CAUSE CUCURBIT YELLOW VINE DISEASE. THESE PEST INSECTS ARE ALSO ASSOCIATED WITH A BENEFICIAL BACTERIAL SYMBIONT, STRAINS OF BURKHOLDERIA SPP., WHICH ARE STORED IN SPECIALIZED GUT CRYPTS. ASSOCIATION WITH BURKHOLDERIA PROVIDES SUBSTANTIAL BENEFITS TO SQUASH BUGS, INCREASING THE INSECTS' SURVIVAL AND DECREASING DEVELOPMENT TIME. UNLIKE MANY BENEFICIAL SYMBIONTS THAT ARE PASSED DIRECTLY FROM PARENT TO OFFSPRING EACH GENERATION, THESE BACTERIA ARE ACQUIRED FROM THE ENVIORNMENT, AND BOTH BENEFICIAL BURKHOLDERIA AND PLANT PATHOGENIC SERRATIA ARE CULTIVABLE. THESE TRAITS MAKE THIS AN IDEAL SYSTEM TO STUDY INSECT-SYMBIONT-PATHOGEN INTERACTIONS. HERE, BUILDING ON RECENT FINDINGS THAT INSECT SYMBIONTS CAN INFLUENCE VECTORING OF BOTH HUMAN AND AGRICULTURAL PATHOGENS IN OTHER SYSTEMS, WE USE THIS TRACTABLE HOST-SYMBIONT-PATHOGEN SYSTEM TO ASSESS: 1) HOW SYMBIONTS INFLUENCE PATHOGEN VECTORING INDIRECTLY BY INCREASING PEST FITNESS, AND 2) WHETHER THESE SYMBIONTS INFLUENCE PATHOGEN VECTORING DIRECTLY BY SUPPRESSING PATHOGEN PROLIFERATION WITHIN THEIR SHARED INSECT HOST. WE COUPLE EXPERIMENTS TESTING INSECT FITNESS AND PATHOGEN GROWTH WITH EXPERIMENTAL EVOLUTION TO SELECT FOR SYMBIONTS THAT DECREASE VECTOR COMPETENCE, AND MOLECULAR APPROACHES TO CHARACTERIZE INSECT RESPONSES TO SYMBIONT AND PATHOGEN ACQUISITION. THIS MULTIFACETED PROJECT DEVELOPS UNDERSTANDING OF HOW SYMBIOSIS, A PROMINENT BIOLOGICAL PROCESS NECESSARY FOR MANY ORGANISMS, AFFECTS THE ABUNDANCE AND SPREAD OF AGRICULTURALLY IMPORTANT INSECTS AND THE PATHOGENS THAT THEY VECTOR.