ACCORDING TO THE FAO, PLANT DISEASES COST THE GLOBAL ECONOMY $220 BILLION AND INVASIVE INSECTS $70 BILLION, ANNUALLY. BACTERIAL PLANT DISEASES SPREAD BY INVASIVE VECTORS ARE ESPECIALLY DIFFICULT TO STUDY DUE TO THE INTIMATE RELATIONSHIPS BETWEEN THE VECTOR, PATHOGEN AND HOST PLANT. RECENT STUDIES HAVE SUGGESTED THAT VECTOR GENETICS AS WELL AS THE SOURCE OF INOCULUM MAY PLAY LARGER ROLES IN DETERMINING PATHOGEN TRANSMISSION TO NEW PLANTS THAN THOUGHT. HUANGLONGBING (HLB), OR CITRUS GREENING DISEASE, IS THE MOST DEVASTATING DISEASE OF CITRUS WORLDWIDE. THE HLB PATHOSYSTEM INVOLVES THREE PLAYERS: THE BACTERIAL PATHOGEN CALLED "CANDIDATUS LIBERIBACTER ASIATICUS" (CLAS), THE ASIAN CITRUS PSYLLID INSECT VECTOR (DIAPHORINA CITRI), AND THE CITRUS TREES (INCLUDING ALL KNOWN VARIETIES OF CITRUS). CITRUS IN THE US IS A $3.40 BILLION DOLLAR INDUSTRY ACROSS FOUR STATES AND IT HAS BEEN HIT HARD BY HLB, WITH THOUSANDS OF JOBS LOST SINCE 2005. DESPITE THE GLOBAL STATUS OF HLB, THERE IS NO CURE, JUST COSTLY AND OFTEN INEFFECTIVE DISEASE PREVENTION AND MITIGATION. IN CALIFORNIA, INTENSIVE TESTING AND "BACK-YARD TREE" REMOVAL PROGRAMS ARE THOUGHT TO BE PREVENTING THE SPREAD OF HLB INTO COMMERCIAL GROVES. HOWEVER, GROWERS AND OWNERS ARE OFTEN WARY OF REMOVING PRODUCTIVE TREES BECAUSE THERE ARE VERY FEW PUBLISHED STUDIES SHOWING TREES ARE THE MAIN DRIVER OF HLB SPREAD IN THE FIELD. ADDITIONALLY, EVIDENCE REPEATEDLY SHOWS THAT BOTH VECTOR AND PATHOGEN POPULATIONS ARE GENETICALLY DIVERSE AND THAT THIS DIVERSITY HAS THE POTENTIAL TO MAKE CONTROL METHODS INEFFICIENT AT BEST - INCLUDING THE USE OF INSECTICIDE SPRAYS. THE ULTIMATE GOALS OF THIS PROJECT ARE TWO-FOLD: 1) TO CLARIFY THE RELATIONSHIP BETWEEN THE IN-FIELD DIVERSITY OF D. CITRI POPULATIONS TO BUILD CONTROL METHODS THAT ARE MORE TARGETED, AND 2) TO ACCESS WHICH ASPECTS OF THE HLB PATHOSYSTEM ARE MOST IMPORTANT TO TARGET FOR CONTROL OF HLB IN THE FIELD. USING GREENHOUSE STUDIES BASED OUT OF CORNELL UNIVERSITY, METHODS WILL UTILIZE MANY REPLICATIONS OF BOTH SINGLE-LEAF ASSAYS AND WHOLE PLANT STUDIES. TO TRACK CLAS IN PLANTS AND INSECTS OVER SPACE AND TIME A COMMONLY USED METHOD OF QUANTIFICATION - QUANTITATIVE POLYMERASE CHAIN REACTION (QPCR) - WILL BE UTILIZED. THE HIGHLY DETAILED DATA WILL BE ANALYZED USING MULTIVARIATE STATISTICAL TESTS, PAIRED WITH A SPECIALLY DESIGNED MATHEMATICAL MODEL, TO EVALUATE SIGNIFICANCE AND DEPENDENCIES AMONG THE VARIABLES. ADDITIONALLY, SPECIALLY INBRED VECTOR POPULATIONS WILL BE CROSSED IN TRADITIONAL BREEDING EXPERIMENTS TO DETERMINE DOMINANCE AND HERITABILITY OF THE VECTOR'S ABILITY TO ACQUIRE AND TRANSMIT CLAS. THIS STUDY STRADDLES THE LINE BETWEEN BASIC AND APPLIED RESEARCH MAKING IT RELEVANT TO BOTH STAKEHOLDERS AND SCIENTISTS. RESULTS FROM THIS PROJECT HAVE THE POTENTIAL FOR HIGH IMPACT IN THE RELATIVELY SHORT-TERM OF 5 YEARS THROUGH UPDATING POLICIES THAT DIRECTLY AFFECT GROWERS, THROUGH IMPROVING HLB MANAGEMENT TECHNOLOGIES AND EFFICIENCY, AND THROUGH DEMONSTRATION OF AMETHOD OF STUDYING A NOTORIOUSLY DIFFICULT INSECT-VECTOR-PLANT PATHOSYSTEM.