Predicting the emergence and arrival of insect pests is paramount for integrated pest management. To achieve this goal, it is important to understand how abiotic factors influence pest dispersal behavior. We investigated the effects of abiotic conditions on flight initiation by the Asian citrus psyllid, Diaphorina citri Kuwayama. We first explored the effect of barometric pressure changes on flight initiation. We used a custom-made barometric chamber and observed the activity of D. citri as measured by the number of psyllids captured on yellow cardboard panels coated with adhesive. We found that psyllid flight initiation changed in response to variations in barometric pressure rather than to differences in stable pressures. D. citri were equally active at 1009 mbar and 1022 mbar. However, D. citri dispersed more as barometric pressure increased, and less when barometric pressure decreased. In a subsequent experiment, we manipulated temperature and relative humidity and observed how D. citri dispersed between citrus plants. Psyllids dispersal increased linearly with temperature. Changes in humidity did not affect dispersal of D. citri. Less than 1% of psyllids dispersed at 15 C, compared to 7.7% at 21 C and 27% at 25 C. The minimal threshold for D. citri to initiate flight is estimated to be 16.5 C. Collectively, our results provide an initial step toward developing predictive models of D. citri movement as influenced by abiotic factors. Densities of an herbivorous pest may be impacted by landscape and orchard architecture. We present two orchard experiments where the densities of the Asian citrus psyllid (Diaphorina citri) were compared depending on: (1) the presence or absence of a windbreak and (2) if the orchards consisted of a solid set re-planting or an orchard with a mixture of mature and reset-replacement trees. (1) Psyllid abundance was measured on the edges of five orchards. The factor investigated was the presence or absence of a windbreak. We observed significantly fewer psyllids on the edges of orchards with windbreaks as compared to those without windbreaks. We found no significant difference in the number of natural enemies between the edges with or without windbreaks, suggesting that windbreaks do not affect densities of psyllid natural enemies. (2) During two consecutive years, we compared the densities of psyllids on young trees less than 3 years of age in a solid set re-planting versus on resets (trees planted in replacement of dead or huanglongbing-infected trees) present randomly within mature orchards. This was conducted in four orchards and among three citrus varieties. More psyllids were found in the solid set re-plantings as compared with on the resets within mature orchards. To our knowledge, this is the first report to demonstrate that the planting strategy of new trees in orchards may impact the populations of a horticultural pest. Overall our data suggest that establishment and conservation of windbreaks might be beneficial to protect orchards from D. citri. The data also suggest that D. citri populations increase more within uniform landscapes of seedling trees as compared with mature orchards with randomly interspersed young seedlings.
The goals of this project were to 1) identify toxins derived from Bacillus thuringiensis (Bt) with toxicity against Asian citrus psyllid (ACP), 2) isolate a peptide that binds to the gut of ACP, and 3) modify the selected Bt toxin with the gut binding peptide to provide an artificial anchor for the toxin resulting in enhanced toxicity. We screened toxin mixtures derived from 35 strains of Bt with diverse insect toxicities and toxin profiles for toxicity against ACP. The bioassay protocol was optimized to avoid toxin precipitation, but control mortality was high in some of the bioassays. Of the 35 strains screened, statistical analysis could only be conducted on data generated for 18 strains. Of these, toxin mixtures derived from a total of six Bt strains showed toxicity to adult ACP at 500 g/mL of proteolytically activated toxin. Individual toxins from one of these strains were identified by LC-MS/MS, cloned, expressed, and tested against adult ACP. Of four individual toxins tested, one showed significant toxicity against adult ACP at 500 ug / ml. Given the smaller size of nymphs and large volumes of phloem ingested, it is expected that toxin efficacy will be greater against nymphs than against adult ACP. ACP mortality was associated with severe disruption of the midgut epithelium for the individual toxin and toxin mixture. The microvilli that line the gut epithelium were disorganized or lost, consistent with the mode of action of Bt-derived toxins. Toxicity also correlated with a drop in honeydew secretion indicative of reduced feeding which is also consistent with Bt toxin effects. We screened a phage display library to identify short amino acid peptide sequences that bind to the gut epithelium of ACP. This screen resulted in identification of four candidate peptides. Of these, two were shown to bind to the ACP gut when fused to the reporter enzyme, mCherry but only one, peptide 15, was found to bind specifically to the gut in competition assays. Peptide 15 was shown to bind to a 50 kDa gut protein. Having identified specific insertion sites in the ACP-active Bt toxin, we constructed a set of modified toxins by addition to- or replacement of- amino acid sequences at four different sites in the toxin, with peptide 15. Some of the modified toxins did not express well using standard expression in E. coli. Expression of these modified toxins using different expression strategies is now underway. Once the expression protocol has been optimized, modified toxins will be purified and tested against ACP. It is expected that peptide 15 will provide a peptide anchor for increased toxin binding to the ACP gut epithelium, resulting in enhanced toxicity against ACP.
Obj. 4. The purpose of this objective is to determine whether prior pathogen or dsRNA exposure inhibits Las acquisition by psyllids. We investigated if D. citri exhibits immune priming and produces a different response to secondary infections and the specificity of that protection. To force D. citri to consume bacteria, they were held on an artificial feeding sachet. The artificial feeding sachet was constructed from a petri dish (35 mm x 10 mm) with the bottom removed and covered with thinly-stretched Parafilm (Bemis NC, Neenah, WI). A and two pieces of thinly stretched Parafilm (Bemis NC, Neenah, WI) with a filter paper disc (2.6 cm dia) with 300 l of diet solution was placed on the Parafilm and covered with an additional Parafilm layer (Russell and Pelz-Stelinski, 2015). The diet solution consisted of 17% sucrose in deionized, distilled water, 30 l/ml of neon green food coloring (McCormick & Company, Inc., Sparks, MD). Total bacteria concentration in diet was 1e7 cells/ml. Diet solutions were placed in a dry heat block at 95 C for 15 min, shaken after 7 min to kill bacteria, and stored at -20 C until used. Diet solutions were plated on nutrient agar plates and incubated at 37 C for 24 to ensure bacteria were not viable. For the duration of the trials, feeding sachet were placed in clear, acrylic 85 mm x 70mm x 30 mm boxes and held in an environmentally-controlled chamber (description of incubator) at 16:8 hr light:dark cycle, 27 2 C, and 60-65% RH. Between 15-25 adult, unmated, sex-separated D. citri were primed by placing them on feeding sachets for 4 days. Surviving D. citri were moved to a second sachet containing 1e6 cells/mL live S. marcescens where they remained until all D. citri were dead. Mortality was recorded once daily. Transgenerational immune priming bioassays were conducted with psyllids placed on artificial diets containing heat inactivated E. coli, M. luteus, or no bacteria. To force D. citri to consume bacteria, they were held on an artificial feeding sachet. The artificial feeding sachet was constructed from a petri dish (35 mm x 10 mm) with the bottom removed and covered with thinly-stretched Parafilm (Bemis NC, Neenah, WI). A and two pieces of thinly stretched Parafilm (Bemis NC, Neenah, WI) with a filter paper disc (2.6 cm dia) with 300 l of diet solution was placed on the Parafilm and covered with an additional Parafilm layer (Russell and Pelz-Stelinski, 2015). The diet solution consisted of 17% sucrose in deionized, distilled water, 30 l/ml of neon green food coloring (McCormick & Company, Inc., Sparks, MD). Total bacteria concentration in diet was 1e7 cells/ml. Diet solutions were placed in a dry heat block at 95 C for 15 min, shaken after 7 min to kill bacteria, and stored at -20 C until used. Diet solutions were plated on nutrient agar plates and incubated at 37 C for 24 to ensure bacteria were not viable. For the duration of the trials, feeding sachet were placed in clear, acrylic 85 mm x 70mm x 30 mm boxes and held in an environmentally-controlled chamber (description of incubator) at 16:8 hr light:dark cycle, 27 2 C, and 60-65% RH. Between 15-25 adult, unmated, sex-separated D. citri were primed by placing them on feeding sachets for 4 days. Data presented here are preliminary, as additional replicates were collected during February and March 2017. These insects are currently being processed and analyzed via QPCR. Offspring of female D. citri that were fed a diet containing M. luteus (n = 17, 2.60E7 1.35E7) or E. coli (n = 18, 2.09E6 8.40E5) had higher CLas titers than offspring of non-primed females (n = 8, 1.22E5 6.20E4). The Ct of plant material was correlated with the titer of CLas in D. citri (b = -0.140, F1,41 = 4.115, p = 0.050, R2 = 0.09). Previously, we demonstrated that the D. citri immune response is induced due to recognition of Gram-positive bacteria, such as M. luteus. Given that M. luteus protected D. citri from S. marcescens, and CLas is also a Gram-negative bacterium, it was expected that CLas titers would be lower in offspring of M. luteus primed adults. In fact, the opposite was observed. Females fed a diet containing M. luteus prior to mating had higher CLas titers and produced offspring that acquired CLas at a much higher rate than those from control or E. coli fed females. This suggests that immune priming with M. luteus infection may facilitate CLas infection.
This project has been reported under ‘Epidemiology and Cultural Control’, but it seems more appropriate to be under ‘Vector Management’, see the category above. Trees and branches to monitor for vegetative and reproductive bud development were selected in the test blocks and initial ratings were established. The Flowering Monitor System provided a first wave flowering full bloom date of February 11 to 20 depending on the location within the Florida citrus production regions, but actually occurred a day earlier. A second wave of flowering was projected to occur from March 8 to 11 depending on location, but this wave was a week early. Warmer than normal weather caused the advanced development and initiation of earlier full bloom. Data collection was started with bud break estimated to occur in early January. It appeared that bud break may be more reliably estimated from initiation of differentiation than from the estimation of full bloom date. Some preliminary plotting showed that in several years mean temperature the first 2 or 3 weeks after initiation of growth was important to determining how many weeks were required to reach full bloom. Dr. L. Stelinski agreed to cooperate in evaluating psyllid control when a block is sprayed at the beginning of spring budbreak rather than later after feather leaves are present. Two properties near Fort Meade were evaluated from early January until present. At one property, 2 blocks were sprayed January 3rd and at the other location two blocks were sprayed January 17th. No adult psyllids were detected by tap counts in 30 days where the spray was applied at budbreak in early January. However adults psyllids were detected at the location where the spray was applied later even though this was a shorter control time. The idea of spraying at budbreak but before feather flush appears to have some merit. We had information for growers on full bloom and 10 % open flowers but did not work out a way to make this information available to bee keepers. We need to develop an extension plan for bee keeper information. We had some success in an associated project in reducing off-season winter bloom by applying gibberellic acid monthly in the fall. We will monitor these trials to see if yields were improved. It did appear however that fewer flowers were present in the first flowering wave also. We will monitor the five locations that growers sprayed and one we sprayed to determine yield of the next crop.
We have continued to investigate movement of Asian Citrus Psyllid (ACP) in response to abiotic and biotic factors. Currently, we are investigating the flight duration as it relates to humidity and influence of wind velocity on movement in the laboratory and field. A flight mill was used to measure the flight of ACP under differing humidity and temperature treatments. We have thus far tested increasing humidity with increasing temperature in the following three treatments: 70 F/relative humidity (RH) 60%, 77 F/ RH 60%, 82 F/ RH 75%. Increasing temperature and humidity caused psyllids to fly longer distances. Psyllids flew the longest distances in the 82 F/ RH 75% treatment but initiated flight 2x more in the 77 F/ RH 60% treatment. This preliminary result suggests that ACP may be flying longer distances on hotter, more humid days but making more frequent short flights on cooler, lower humidity days. We are currently expanding this data set with additional temperature and RH treatments. We are investigating the influence of wind on ACP dispersal in the laboratory and field. In the laboratory, we are using a wind tunnel set up. ACP are allowed to settle on a young citrus plant for 24 hours before exposed to a wind treatment for 24 hours. To track their dispersal, a sticky trap is set up behind the plant and to the surrounding cage at 1, 2, 3, and 24 hours of wind exposure. We have tested the following wind velocities: 1.8 meters per second, 1.5 m/s, 1 m/s, and 0.38 m/s. At higher wind velocities, ACP does not move and the most movement occurs in no wind controls. The results from this study currently indicate that ACP is dispersing most at 0.38 m/s. In the field, we are assessing ACP movement using a wind vane fitted with sticky traps alongside an anemometer. The wind vane shifts direction to align with the wind. We have been preliminarily field testing this apparatus with great success. Currently, in low density winter ACP populations, it appears that the ACP are moving with the wind and moving more at wind velocities under 1m/s.
The objective of this study was to determine differential detoxification enzyme levels among different abdominal color morphs (orange/yellow, blue/green and gray/brown) of Asian citrus psyllid (ACP). Glutathione S-transferase, cytochrome P450 and esterase activity were measured. First, we used a topical bioassay to determine the insecticide susceptibility to adults of three color morphs. The insecticides chosen were from four different modes of action. Three color morphs of adult ACP were collected in the field from Lake Alfred, FL. Tested insecticides were of analytical grade and included bifenthrin (99.8%), dimethoate (99.8%), flupyradifurone (99.5%) and aldicarb, (99.7%). The LD50 value and 95% fiducial limits for aldicarb (carbamate) were1.52 ng/ l (0.86-2.74) for orange/yellow; 2.06 ng/ l (1.17-3.71) for blue/green and 2.29 ng/ l (0.52-12.37) for gray/brown ACP. The LD50 value and 95% fiducial limits for diamethoate (organophosphate) were 0.32 ng/ l (0.18-0.56) for orange/yellow; 0.50 ng/ l (0.28-0.91) for blue/green and 0.62 ng/ l (0.35-1.12) for gray/brown ACP. For bifenthrin (pyrthroid), the LD50 value and 95% fiducial limits were 0.10 ng/ l (0.06-0.18) for orange/yellow; 0.13 ng/ l (0.07-0.24) for blue/green and 0.13 ng/ l (0.07-0.23) gray/brown ACP. The LD50 value and 95% fiducial limits for flupyradifurone (butenolid) were 3.79 ng/ l (2.03-7.52) for orange/yellow, 4.78 ng/ l (0.92-46.9) for blue/green and 6.16 ng/ l (3.30-12.50) for gray/brown ACP. The susceptibility to aldicarb, dimethoate and flupyradifurone was significantly higher for the orange/yellow morph as compared to blue/green and gray/brown morhphs. Secondly, we quantitatively measured the detoxification enzyme activity levels of orange/yellow, blue/green and gray/brown color morphs to determine difference between the physiological states of these three color morphs. Cytochrome P450 activity was quantified and expressed in terms of general oxidase level. A heme peroxidation method was used to indirectly determine the P450 activity using substrate of 3,3′,5,5′-tetramethylbenzidine (TMBZ). General esterase activity was measured using 4-nitrophenyl acetate (pNPA) as a substrate. Glutathione S-transferase activity were conducted using CDNB (1-chloro-2.4-dinitrobenzene) (CDNB) as the substrate. GST activity was significantly lower in orange/yellow color (299.70 1.24 mol/min/mg protein) than gray/brown (350.86 1.19 mol/min/mg protein) and blue/green (412.25 1.37 mol/min/mg protein) ACP adults. Likewise, mean cytochrome P450 activity was significantly lower in gray/brown (0.152 0.006) and blue/green (0.149 0.005) equivalent units (EU) cytochrome P450/mg protein than orange/yellow (0.179 0.008) equivalent units (EU) cytochrome P450/mg protein. Mean esterase activity was significantly higher in blue/green (416.72 5.12 mol/min/mg protein) and gray/brown (154.25 5.46 mole/min/mg protein) than orange/yellow (282.56 2.93 mol/min/mg protein) ACP. Results indicated the GST and esterase activity may be correlated with insecticide susceptibility levels. The study shows that activity levels of three important detoxifying enzymes in ACP are potentially different depending on the color morph and may influence insecticide efficacy depending on differential abundance in the field. However, further investigations are needed to compare expression levels of associated genes between difference color morphs. Importantly, insecticide resistance does not appear to be shifting populations of ACP toward more resistant color morphs based on our observations thus far. Work continues on the field investigation comparing different insecticide rotational schemes. We completed the latest rotation sprays in October 5, 2016 but were unable to collect sufficient numbers of psyllids to assess for insecticide resistance. Currently, we are rearing insects collected from the different plots to obtain sufficient numbers for testing in the laboratory. These laboratory cultures established from our field experiments will allow us to determine which rotation schedules tested are best to minimize the chance of resistance development in the field. We expect to have more results at the end of next quarter to begin answering this question.
Report for period ending 3/2016 During this reporting period we setup an series of growth chamber experiments to evaluate effect of seasonality on neonicotinoid uptake by citrus trees in the laboratory. This is being done to determine if there is any effect of season and/or transpiration rate to neonicotinoid expression in citrus foliage for each of the three neonicotinoid chemistries. Citrus (v. Hamlin / r.s. Swingle) was planted to 3-gal pots containing a custom soil blend (50% sand, 50% potting media). Potted plants were divided between two growth chambers with unique environmental conditions: 1) winter-like conditions characterized by low temperature, short day length, dry soils, and low light intensity (reflect January 30-year average in Immokalee, Florida), and 2) summer-like conditions characterized by high temperature, long day length, wet soils, and high light intensity (reflect August 30-year average in Immokalee, Florida). Plants in each growth chamber were arranged in a randomized complete block design (RCBD) with 4 treatments and 4 replicates. Each plot consisted of three citrus trees. A single insecticide application was made to the soil using 8 fl oz of insecticide solution per tree. Leaf tissue samples (n=6 leaves per tree) were collected weekly until 4 weeks after application. Leaves were excised to differentiate concentrations between the leaf center and leaf margin. In addition to quantifying neonicotinoid expression, the transpiration rate of 4 individual trees were measured in each growth chamber using a Dynamax Sap Flow meter system. A single tree from each treatment was represented in each growth chamber. The initial and final canopy volume and stem diameter for each of the 8 trees was recorded.
Report for period ending 9/2015 At the beginning of this reporting period we setup a greenhouse pot study to compare the spatial distribution of insecticide within citrus leaves. Previous preliminary work we conducted suggested that there is likely differences in the distribution of imidacloprid within leaf tissue that may affect the lognevity and amount of control provided by soil drench applications. Here, we examine this further and also examine movement of thiamethoxam and chothianidin as well. The insecticide concentration along the leaf margin was compared to the concentration in the leaf center. Citrus (v. Hamlin / r.s. Swingle) was planted to 3-gal pots containing a custom soil blend (50% sand, 50% potting media). The study was arranged in a randomized complete block design (RCBD) with 4 treatments and 4 replicates. Each plot consisted of 4 citrus trees 3-5 ft in height. A single insecticide application was made to the soil using 8 fl oz of insecticide solution per tree. Leaves were sampled prior to the insecticide application to ensure no insecticide was present, and again every 7 days, until the concentration fell to undetectable levels. At each sampling event, four leaves were removed from the upper canopy of each of the 4 trees within each plot. Leaves will be dissected into two regions: 1. leaf margin region (area 0.5 cm from leaf edge), and 2. leaf center region (area within 0.5 cm on each side of the mid-vein). Concentrations were analyzed using Liquid Chromotography-Mass Spectrometry. Due to number of samples to be analyzed, this experiment will be completed during the next reporting period.
Report for period ending 12/2015 During the previous reporting period, we established an experiment in the greenhouse to compare the spatial distribution of soil applied neonicotinoids within leaf tissues. LC-MS-MS analysis of all of these samples is still ongoing, but we are fairly confident that the preliminary information presented in the following is an accurate representation of what the final results will be. For thiamethoxam, peaked around 2 weeks after application, and slowly declined over the next 8 weeks. The levels of material seen in the plants tissues analyzed across all samples dates was sufficient to control ACP. When tissue samples were separated and analyzed by either leaf margin or leaf center, there was no significant difference between the two for thiamethoxam. For imidacloprid, the concentrations did not peak until 5 weeks after application but even 1 week after application were high enough to control ACP and remained high enough through week 8 of the study. For imidacloprid there was a significant difference in product concentration between the leaf center and leaf margin which we had anticipated based on our previous work. Similar to imidacloprid, clothianidin concentrations peaked 5 weeks after application but were probably not high enough to control ACP 1 week after application. By two weeks after application, concentrations were high enough to have an effect on ACP. Residues remained high enough to control ACP through week 8 of the study. Similar to imidacloprid, clothianidin concentrations were significantly different between the center of the leaf and leaf margins. These results confirmed that large differences do exist between the three soil-applied neonicotinoids in terms of how they move in the plant, become distributed within leaf tissues, and the duration of control. This information will be used to design the next set of experiments examining these and other more pertinent questions under field growing conditions.
Report for period ending 3/2016 During this reporting period we setup an series of growth chamber experiments to evaluate effect of seasonality on neonicotinoid uptake by citrus trees in the laboratory. This is being done to determine if there is any effect of season and/or transpiration rate to neonicotinoid expression in citrus foliage for each of the three neonicotinoid chemistries. Citrus (v. Hamlin / r.s. Swingle) was planted to 3-gal pots containing a custom soil blend (50% sand, 50% potting media). Potted plants were divided between two growth chambers with unique environmental conditions: 1) winter-like conditions characterized by low temperature, short day length, dry soils, and low light intensity (reflect January 30-year average in Immokalee, Florida), and 2) summer-like conditions characterized by high temperature, long day length, wet soils, and high light intensity (reflect August 30-year average in Immokalee, Florida). Plants in each growth chamber were arranged in a randomized complete block design (RCBD) with 4 treatments and 4 replicates. Each plot consisted of three citrus trees. A single insecticide application was made to the soil using 8 fl oz of insecticide solution per tree. Leaf tissue samples (n=6 leaves per tree) were collected weekly until 4 weeks after application. Leaves were excised to differentiate concentrations between the leaf center and leaf margin. In addition to quantifying neonicotinoid expression, the transpiration rate of 4 individual trees were measured in each growth chamber using a Dynamax Sap Flow meter system. A single tree from each treatment was represented in each growth chamber. The initial and final canopy volume and stem diameter for each of the 8 trees was recorded.
Report for period ending 6/2016 Over the past year, studies using electropenetrography (EPG) studies have been conducted with the goal of determining how much imidacloprid is needed in leaf tissues to control ACP, in particular to disrupt psyllid phloem-feeding behaviors. During these studies, we have continued to increase the dose of imidacloprid delivered to plants in order to reach the point where 100% of psyllids are incapable of reaching the phloem. However, the results obtained to date using EPG suggest that even at unrealistically high levels of imidacloprid applied to the plant, an average of 2% of the psyllids are still likely to perform some feeding behaviors in phloem. However, our data suggests that because the proportion is so low, and not every feeding bout by a psyllid results in infection, this use of imidacloprid to reduce infection in young tree plantings is still a very useful tool. However, some results obtained here suggest that the soil-applied neonics ability to prevent infection may be due more to feeding deterrence rather than direct mortality. Thus, we initiated experiments using an artificial diet-based bioassay to develop a dose-response curve for the three neonics versus the asian citrus psyllid. The majority of time spent this quarter was in perfecting the artifical diet system building upon the success of other researchers who have used such diets for studying ACP. Our goal here is to develop a feeding-based LC50 and LC90 for imidacloprid, clothianidin and thiamethoxam. THese LC50/90 values will then be compared to those previously reported values for contact bioassays using either leaf dip or vial assays. Concurrent with this work, we are continuing to analyze the large backlog of leaf samples gathered from our ongoing field studies where we are investigating the uptake of the three neonics at different times of the year, distribution of the three neonics within a tree, and appropriate rate of product applied based on tree size. We literally have thousands of samples in the freezer awaiting analysis. We continue to run samples as fast as the machine can analyze them.
Report for period ending 9/2016 In the last reporting quarter we began work with artificial diets to develop a dose response curve to help determine the amount of the three neonicotinoids that are needed in order to control ACP. We were able to master the use of an artificial diet to deliver varying concentrations of imidacloprid, thiamethoxam and clothianidin to psyllids as they feed to model the toxicity and behavioral changes that would occur when feeding on treated plants. The results from this study corroborated our findings last reporting period where we used EPG to demonstrate that the soil-applied neonics primarily control psyllids through feeding deterrence as it took large levels of all three insecticides to kill 90% of the population. Of special interest, we found that the LC50 and LC90 values for feeding exposure to neonics were far greater than the values obtained for contact assays. This discovery has led us to pursue two additional studies this next quarter where we will use our feeding bioassay against psyllids from different parts of the state to see if the results from our lab colony are consistent with the wild populations of psyllids in Florida. We will also begin using the artificial diet bioassay in our EPG studies to get a better gauge of exactly what concentrations of insecticides psyllids must be exposed to to quit feeding…but not necessarily die from that exposure. Previously this could only be estimated in past studies where plants were treated with varying doses of insecticides. Now, with the artificial diet assay, we can more reliably determine the amount required to cause psyllids to withdraw their mouth parts from treated plants. Concurrent with this work, we are continuing to analyze the large backlog of leaf samples gathered from our ongoing field studies where we are investigating the uptake of the three neonics at different times of the year, distribution of the three neonics within a tree, and appropriate rate of product applied based on tree size. We literally have thousands of samples in the freezer awaiting analysis. We continue to run samples as fast as the machine can analyze them.
Report for period ending 12/2016 During this quarter we surveyed ACP populations across the state to compare the wild populations of ACP with our laboratory colony in terms of amount of the three neonics required to control ACP based on method of delivery. Sites chosen to collect psyllids included locations in Vero Beach, Lake Placid, Lake Alfred and LaBelle FL. In all cases, the wild psyllid populations responded in a similar manner to our laboratory colony with the LC50 and LC90s for ingestion being far greater than those values for the contact assays. We also did note some variation in the amount of product required to reach an LC90 value. This results suggests that more monitoring should be conducted for potential shifts in psyllid susceptibility to the nenicotinoid insecticides. We have also been making great progress with our EPG studies of psyllid feeding on artificial diets to determine the amount that is needed to cause psyllids to quit feeding (not necessarily die) and thus reduce transmission probabilities. Here we have been able to identify the waveforms produced that are drastically different from those in plants and then begin record and analyze psyllid feeding on artifical diets containing varying levels of iinsecticides to develop the LC50/90 data for mouthpart withdrawal. As previously reported…we are continuing to analyze the large backlog of leaf samples gathered from our ongoing field studies where we are investigating the uptake of the three neonics at different times of the year, distribution of the three neonics within a tree, and appropriate rate of product applied based on tree size. We literally have thousands of samples in the freezer awaiting analysis. We continue to run samples as fast as the machine can analyze them.
The objective of this research project is to investigate and develop a potential non-phytotoxic, environmentally-friendly film-forming ACP repellent solution for preventing HLB infection. In the last reporting period, OS-SG 15 and OS-SG 16 were tested for their plant safety and surface coverage , along with material characterization using infrared spectroscopy. Testing of those formulations were compared to commercial control, Surround WP. Preliminary results for this testing revealed comparable, but no significant improvement over commercial control for surface coverage. With surface coverage being of paramount importance in preventing infection via ACP-leaf interaction, further material development was needed. During this current reporting period , a new formulation, OS-SG 17 is being developed to overcome the weaknesses found in previous versions of the material. A new, all natural EPA approved silica source (“Fumed Silica”) was used as a silica substrate to create a multi-layered silica gel matrix when combined with our previous silica composite. The hydrophobic nature of the “fumed silica” is expected to increase the surface coverage of the new OS-SG 17 composite. Different iterations of OS-SG 17 are being studied as controls using our previously used EPA approved polymer to improve stability, dispersion and rainfastness. This new formulation is expected to display high colloidal stability in aqueous solution, high surface coverage and moderate rain-fastness properties. It was characterized using UV-Vis and FTIR spectroscopy. The colloidal stability of the formulation was checked via measuring %Transmittance (%T) of the supernatant collected from the solution left undisturbed. The formulation revealed less than 50 % transmittance up to 8+ hours which was found to be better compare to commercial control -Surround WP. Testing of this new version is in progress to ascertain the extent of its surface coverage and confirm that it does not create an unfavorable temperature increase on leaf surfaces. Phytotoxicity studies were conducted using a Panasonic Environmental Test Chamber (Model MLR- 352H) to control light intensity, humidity and temperature cycling to simulate summer conditions (85% RH, 32 Celsius). OS-SG 17 formulation did not cause any plant tissue damage at the applied rates, matching the commercial control. Next we will conduct ACP repellent studies using psyllid containment cages which have been acquired recently.
Irrigation water acidification (target pH, 7.5, 6.0, 5.0, and 4.0) continues at two citrus groves (one a 20 year-old Hamlin sweet orange trees predominately on Swingle rootstock and the second a three year old Hamlin sweet orange trees on Swingle rootstock). The last sulfur application in this study will be made to selected treatment blocks in January 2017. Soil samples taken prior to the summer 2016 sulfur application in June indicated that plots receiving both acid injection and sulfur had soil pH significantly lower than plots receiving only irrigation water acidification. Soil samples taken in December indicated that soil pH in plots receiving both irrigation water acidification and sulfur application had similar soil pH. These results would indicate that the relatively slow release sulfur product (Tiger 90) reduced soil pH below that achieved by irrigation water acidification only but lasted less than six months. Root density samples taken in June indicate a significantly greater root length density with lower soil pH. These results indicate a positive correlation between root density and reduction in soil pH from greater than 7.0 to less and 5.0. Leaf Ca, Mg, Mn, and Zn in November samples were greater for trees treated with both irrigation water acidification and sulfur application compared with irrigation water acidification only. These results verify previous finding that leaf nutrient status is negatively correlated with soil pH. Thus, tree nutrient status is increased with lower soil pH. Tree size and fruit drop measurements indicate significant growth with reduced soil pH to approximately 5.0 with no additional decrease below that level. A talk on methods of irrigation water acidification and expected improvements on citrus nutrient status will be given on January 19, 2017 to growers attending a nutrient BMP meeting at the SWFREC. Since previous grower presentation, numerous personal contacts have been made with individual citrus growers to continue, alter or initiate soil acidification projects in groves throughout the state.
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