The overall goal is to determine the effect of antimicrobials on ACP biology, vector capacity, and behavior. Objective 1: Quantify the effect of citrus antimicrobials on vector fitness. As previously reported, this objective has been completed. Data analysis is underway and a manuscript is being prepared for publication. Objective 2: Determine the effect of antimicrobials on Las transmission. This objective will determine whether ACP feeding on antibiotic treated infected citrus plants will be less likely to transmit Las. Laboratory acquisition assays were completed in July 2020. Analysis of CLas acquisioton will be completed following DNA extraction of insect tissues and PCR to determine CLas infection.Field acquisition assays continued during this quarter. Eight-year-old CLas-infected citrus trees have received foliar applications (May 2019 September 2020) of streptomycin, oxytetracycline, or receive no antimicrobials (Control). One day after the application, ten CLas-free insects per plant from a laboratory colony were caged on young leaves (flush) of treatment and control trees to analyze ACP survival, CLas-acquisition in ACP P1 and F1 progeny, the total trees sampled consisted of 5 individual trees per treatment. In microcentrifuge tubes containing 1 mL of 80% ethanol, ACP adults were collected individually and then stored at -20°C for subsequent CLas detection using real-time PCR. CLas-acquisition experiments were replicated from June 2019 to September 2020. All sample replicates have been collected according to schedule, and are currently being processed to analyze the CLas-infection rate. The final results will be available in the next report. Objective 3: Determine the effect of antimicrobials on plant response and associated ACP behavior. Bioassays were carried out using 4 year old Citrus sinensis L. Osbeck cv Valencia grafted onto US-812 rootstocks, maintained at 23 ± 3 °C, 60RH, and a 16:8 h (Light: Dark) photoperiod. Trees were watered twice per week, and fertilized once per month with an alternating schedule of a 24-8-16 (NitrogenPhosphorusPotassium) Miracle-Gro All Purpose Plant Food (Scotts Miracle-Gro Products, Marysville, OH) and a 10-10-10 (NPK) granular fertilizer (Growers Fertilizer Corp., Lake Alfred, FL) Colonies of CLas-free of Asian citrus psyllid (ACP) were maintained on C. sinensis L. Osbeck cv Valencia at 26 ± 2°C, 60-65% RH, and a 16:8 h (Light: Dark) photoperiod in a greenhouse. In order to determine the presence/absence of the CLas pathogen in our lab reared ACP, a sub-sample of 40 adult insects were collected for DNA extraction and later TaqMan qPCR assay were performed according with laboratory protocols. Experiments were conducted to determine whether the antibiotic applications to sweet orange, C. sinensis, affect subsequent insect host preference and acceptance behaviors. Six trees (biological replicates) were evaluated per treatment. Individual trees were sprayed with FireWall (Streptomycin sulfate), FireLine (Oxytetracycline), or control (adjuvant); and then relocated into a growth chamber maintained at 23 ± 3 °C, 60RH, and a 16:8 h (Light: Dark) photoperiod until further bioassays. To test the insect choice response 20 days post-treatment, a pair of antibiotic- and control- plants were transferred to a behavioral chamber (dimensions?) with 70 ACP adults. Insects were allowed 24 hours to search out and settle on plants. Afterward, all insects found feeding or control plants were counted. Our results showed that antibiotic treatments rendered treated plants significantly less acceptable to infestation by ACP adults than comparable controls. In direct comparisons with control plants, Streptomycin Streptomycin (FireWall), Oxytetracycline (FireLine), and the combination of Streptomycin/Oxytetracycline (FireWall/FireLine) each reduced plant acceptability to released psyllids by 57-63%. Currently, we are investigating whether longer-terms treatment with antibiotics further reduces plant acceptability to the vector. We are also investigating the possible mechanisms explaining why plants treated with antibiotics are less acceptable to the vector. Overall, the results indicate that antibiotic treatments may have beneficial impact by reducing vector feeding on plants (which should reduce pathogen onoculation) in addition to their direct effects on the pathogen.