X-DISEASE PHYTOPLASMA (CANDIDATUS PHYTOPLASMA PRUNI), THE CAUSAL ORGANISM OF X-DISEASE IN STONE FRUITS OR "BUCKSKIN" AND "LITTLE CHERRY DISEASE" IN CHERRIES, RECENTLY RE-EMERGED IN THE US AND IS CURRENTLY DEVASTATING CHERRY PRODUCTION IN THE PACIFIC NORTHWEST. DISEASED TREES NEVER RECOVER, THEREFORE CONTROL METHODS RELY ON INFECTED TREE REMOVAL AND BROAD-SPECTRUM CHEMICAL CONTROL OF THE LEAFHOPPER VECTORS. OVER 1,000 ACRES OF TREES HAVE BEEN REMOVED IN THE LAST FIVE YEARS AND $18 MILLION LOST IN REVENUE IN 2020 ALONE DUE TO X-DISEASE.RESEARCH ON LEAFHOPPER-X-DISEASE PHYTOPLASMA INTERACTIONS IS NEARLY A HALF-CENTURY OLD LEAVING IMPRECISE EPIDEMIOLOGICAL KNOWLEDGE, AND HINDERING OUTBREAK MITIGATION EFFORTS. ONE INTERESTING FINDING IS THE PHYTOPLASMA REDUCES THE LEAFHOPPER'S LIFESPAN; THEREFORE, ENHANCING THE PHYTOPLASMA'S VIRULENCE THROUGH COINFECTION WITH ANOTHER INSECT PATHOGENCOULD REDUCE VECTOR CAPACITY. THIS PROJECT UTILIZES A COMBINATION OF MOLECULAR, PHYSIOLOGICAL, AND ECOLOGICAL APPROACHES TO DESCRIBE AND UNDERSTAND THE DISEASE CYCLE OF X-DISEASE WITHIN THE LEAFHOPPER VECTORS AND DEVELOP SUSTAINABLE VECTOR CONTROL TECHNIQUES TO LIMIT TRANSMISSION AND OUTBREAKS.THROUGH LABORATORY AND GREENHOUSE EXPERIMENTS I WILL DESCRIBE THE X-DISEASE INFECTION CYCLE WITHIN THE LEAFHOPPER VECTOR FROM ACQUISITION TO TRANSMISSION IN BOTH X-DISEASE PHYTOPLASMA ONLY INFECTED LEAFHOPPERS AND LEAFHOPPERS COINFECTED WITH A FUNGUS. SPECIFICALLY, I WILL USE PROBES TO FLUORESCENTLY MARK PATHOGEN DNA WITHIN THE VECTOR AT VARIOUS TIME POINTS POST ACQUISITION TO VISUALIZE AND DETERMINE THE PATHWAY OF INFECTION, TIME TO THE VECTOR BECOMING INFECTIOUS, AND INTERACTIONS OF TWO PATHOGENS WITHIN A HOST. THE RESULTS FROM THESE EXPERIMENTS WILL DETERMINE HOW LONG IT TAKES FOR THE VECTOR LEAFHOPPERS TO BECOME INFECTIOUS AFTER UPTAKE OF THE PATHOGEN WHICH IS CRITICAL TO INFORMING X-DISEASE MANAGEMENT STRATEGIES. UNDERSTANDING THE PATHWAY OF INFECTION PROVIDES INSIGHTS INTO PHYTOPLASMA DISEASE ECOLOGY AND CAN OPEN NEW AVENUES FOR CONTROL OPTIONS WITHIN THE LEAFHOPPER VECTOR. ASSESSING EFFECTS OF COINFECTION WILL ELUCIDATE THE EFFECTS OF MICROBIAL CONTROL AGENTS ON THE VECTOR AND X-DISEASE PHYTOPLASMA. ACCOMPLISHING THESE OBJECTIVES WILL BUILD THE FOUNDATION FOR SUSTAINABLE X-DISEASE MANAGEMENT PROGRAMS AND PROVIDE INSIGHT INTO OTHER ARTHROPOD VECTORED PHYTOPLASMAS.