Objective 2. Determine the effect of antimicrobials on Las transmission.
Hypothesis: ACP will be less capable of transmitting CLas after feeding on antimicrobials because trees treated with antimicrobials are more likely to have lower CLas titers for acquisition.
Eight-year old CLas-infected citrus trees have received six foliar applications (May-December) 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 tree per group. Survival of ACP and CLas-acquisition were replicated twice from June to November. During the first replicate, ACP P1 adults were collected on the 26th of June. Approximately two weeks later, five to ten ACP adults corresponding to the F1 progeny were collected. The second (July), the third (September), fourth (October), and the fifth (November) replicates were collected using the same conditions previously described. 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. Concurrently, the titer of CLas had been monitored at the same time-points using three leaves per tree to determine the CLas-infection rate. Currently, psyllids collected from June through November are being processed to analyze the CLas-infection rate.
Currently, psyllids collected from June through November are being processed to analyze the CLas-infection rate.
Objective 3: Determine the effect of antimicrobials on plant response and associated ACP behavior.
The objective of this experiment is to determine whether antimicrobial treatments applied to citrus plants affect behavior of Asian citrus psyllid that may change plant susceptibility to ACP infestation or pathogen inoculation. Two antimicrobial treatments are being investigated. These are Fireline (oxytetracycline HCL) and Firewall (streptomycin sulfate). Each is being applied to trees at label recommended rates with recommended adjuvants. To date, all treatments have been applied as foliar sprays; however, experiments are in progress and other methods of treatment application will be explored. Treatments are being applied to two year old Citrus sinensis L. Osbeck cv Valencia grafted onto US-812 rootstock. Separate experiments are underway comparing all uninfected (treated with antimicrobials versus untreated) versus all infected plants. In the first experiment, we compared response of ACP to the odors of treated and control plants 4, 6, and 8 weeks after treatment with Fireline. C. sinensis plants were placed in 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 using either all uninfected or all infected plants. ACP response was evaluated with the T-maze olfactometer to determine whether Fireline affected ACP preferences for antimicrobial-treated versus untreated plants. There was no difference in behavioral response of ACP to plants treated with Fireline versus untreated controls 4, 6, and 8 weeks after treatment. These results were consistent when both uninfected and CLas-infected treatment and control plants were compared. Experiments are still in progress with Firewall. Thus far, it does not appear that application of antimicrobial treatments (Fireline) to citrus should induce an effect on plants that would cause a consequential change in the behavior of the vector to increase or decrease their preference for treated versus untreated trees, based on the odors released by trees.