The objective of this study was to develop an insecticide rotation with different modes of action as a resistance management strategy for Asian citrus psyllid (ACP) in Florida. We selected two large scale experimental sites in two citrus groves in central Florida. One site was in Lake Alfred (Polk County) on CREC property planted with the cultivar Hamlin. The second site was in Wachula (Hardee County) and was planted with Valencia selections. The Lake Alfred site has trees that are bearing fruit. At the Wauchula site, the trees are non-bearing. At each location, three rotation schemes were established ion 4.9 acres each in Lake Alfred and on 4.2 acres each in Wachula. For sampling, we established 6 replicates per treatment in Lake Alfred and 4 replicates in Wachula.
The insecticides were applied in two rotational schemes with five different modes of action. The third treatment was to apply different neonicotinoids with no change in the mode of action. Rotation A consisted of dimethoate followed by cyantraniliprole, fenpropathrin, diflubenzuron and imidacloprid. Rotation B consisted of fenpropathrin followed by dimethoate, imidacloprid and diflubenzuron. No rotation consisted of thiamethoxam, clothianidin, thiamethoxam, imidacloprid and clothianidin. At this point we have completed two applications at both locations.
Prior to the insecticide applications, the plots were monitored for ACP adults using tap sampling. Weekly monitoring was initiated on March 20, 2019 in Wachula and April 1, 2019 in Lake Alfred. When the average number of adults per tap reached 0.4 insects the appropriate insecticide was applied using an airblast sprayer by the cooperator. Also, ACP adults were collected and a baseline insecticide susceptibility was determined and compared with our susceptible laboratory population using a leaf dip assay. Five to six concentrations of each insecticide was tested and replicated 5 times. We found low to moderate resistance for thiamethoxam (RR > 20), imdaclorprid (RR > 10), clothianidin (RR > 10) and dimethoate (RR > 10). We found very low resistance to the other insecticides in the field populations (RR < 5). Finally, before application, morphological measurements on adult ACP were made At least 50 individuals were measured. Body length, abdominal length, wing length, femur length and head width were measured for laboratory susceptible cultures and for both field populations. The results indicated that the abdominal length, wing length and femur length was greater in the laboratory population compared with both field populations. The current investigation is ongoing. It will continue to monitor ACP management and resistance among the treatments and locations described above. Our goal is to find a more refined method of effective insecticide resistance management of ACP that also shows highest efficacy. Our newly developed protocols on suppression of ACP populations by stabilizing or reducing resistance will be communicated with growers when the results are properly verified experimentally.