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. Experiment 2.1 Acquisition assays. Several more replicates of these experiments are needed to complete this experiment. These replicates be conducted begining July 2020.Experiment 2.2. Field study. Eight-year-old CLas-infected citrus trees have received six foliar applications (May 2019 May 2020) of streptomycin, oxytetracycline (Treatments), or receive no antimicrobials (Control). 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. The survival of ACP and CLas-acquisition were replicated twice from June 2019 to March 2020. However, the UF/IFAS Citrus Research and Education Center (CREC) closed on March 23rd due to COVID-19, limiting our access to the center and equipment. The second sampling (July 2019), the third (September 2019), fourth (October 2019), the fifth (November 2019), the sixth (January 2020), and the seventh (March 2020) replicates were collected and are being processed to analyze the CLas-infection rate.Objective 3: Determine the effect of antimicrobials on plant response and associated ACP behavior. Experiment 3.1 Host choice bioassays. We compared the responses of Asian citrus psyllid (ACP) adults to the odor sources from sweet orange seedings that had been treated with Fireline (oxytetracycline HCL) or Firewall (streptomycin sulfate) versus a water (blank control). All treatments were applied to seedings as foliar sprays at proportionally adjusted label rates. Each treatment was compared relative to an untreated control by placing plants into glass chambers with air throughput delivered into a psyllid two-choice (T-maze) behavioral assay. In this manner, ACP were tested to determine their response to treated versus control plants. Separate experiments were conducted with uninfected and Las-infected plants. Four replicate plants were tested for the uninfected plants and three replicate plants were completed for Las-infected plants plants. The response of 30 ACP adults were evaluated with the T-maze olfactometer per replicate to determine whether antimicrobials affect ACP preferences for antimicrobial-treated versus untreated plants. The majority (> 85 %) of ACP responded to the odors of either uninfected or Las-infected citrus plants compared with a blank control. Also, more ACP were attracted to the odors from Las-infected plants than uninfected plants. These resuls confirmed our previous findings and verified that our experimental set up was working properly. When comparing seedlings that were treated with antimicrobial treatments versus untreated plants, there was no difference in ACP attraction to Fireline-treated versus untreated plants, whether or not they were infected with CLas. Similarly, there was no difference in response of ACP adults to Firewall-treated versus control plants when tests compared all uninfected plants and when tests compared all Las-infected plants. These initial results would suggest that treating plants with antimicrobials should not recruit psyllids from a distance, using odors as cues, to those treated plants and thus should not create greater psyllid infestation on treated plants. Followup investigations are currently under way to determine if psyllid host preference between antimicrobial treated versus untreated plants differs when psyllids are allowed to choose between treated and untreated plants in open air cage experiments. Although the laboratory olfactometer experiments would suggest that antimicrobial treatments did not affect the odor of the plants to indirectly affect psyllid preference, psyllids also use several other senses, in addition to smell, when selecting hosts for feeding and egg-laying. In fact, in recent years, we have come to understand the vision and taste are in many cases more important than smell for psyllids to select an appropiate host. We are evaluating the same treatments as above, comparing psyllid response to antimicrobial-treated and untreated plants, in custom made cage assay currently. Our initial tests in these cages are being conducted with all infected plants, based on the initial olfactometer studies and since the treatments are in practice intended for treated CLas-infected plants.