The overall objective of this project was to evaluate the impact of insecticidal sprays for psyllid control on non-target pests, beneficial insects and mites. Sampling of 4 large replicated blocks of mature citrus in conventional groves was conducted in plots either untreated or treated with foliar sprays of insecticides, horticultural oils against psyllids, citrus leafminer (CLM), citrus rust mites (CRM), citrus red mite, predatory mites, snow scale, chaff scale, Glover scale, purple scale, citrus blackfles, whiteflies, mealy bugs, and aphids as well as their natural enemies. Stem tap, vacuum, sticky traps, shoot examination and predator exclusion techniques were used to monitor populations of psyllids and non-targets. Fruit damage was also evaluated. Two of the four study sites were in Hendry County and one each in Lee and Collier Counties. In addition 16 trials were conducted to compare effects of 164 treatments of recommended and experimental insecticides on ACP, CLM and natural enemies at SWFREC (Collier County) or in a commercial grove in Hendry Co. Studies at conventional groves showed that monthly sprays of selective recommended insecticides for control of ACP adversely affected natural enemy populations, reducing predation on ACP immature stages thus increasing projected growth rates of pest populations surviving the sprays. Similar negative impacts on generalist predators or species-specific parasitoids of other pests were observed. Arboreal ant which serve as important predators of CLM and its introduced parasitoid Ageniaspis citricola were most affected with calendar sprays. Predation on CLM was reduced from 90% to 70% by calendar sprays. Increase in populations of other pests such as CRM, citrus red mite, purple and chaff scales was also observed with calendar or grower standard sprays. Studies conducted at SWFREC showed that effective commonly used and experimental insecticides cause significant reduction in ACP populations compared to the untreated control for three to four weeks. However few products, such as Delegate, Movento, Agri-flex and Voliam flexi, also provided even short term (2-week) reduction in CLM populations. In general, most calendar or grower standard and experimental treatments suppressed ACP and natural enemies but did not reduce non-target pests in most situations, creating the need for additional applications which caused even greater impact on predators and parasitoids warranting need for selective insecticides. However, ACP populations were very low at most times and fewer or no sprays would have been justified had thresholds existed. Some publications are listed below and others being prepared or available at http://www.imok.ufl.edu/entomology/ Qureshi, J. A., B. Kostyk and P. A. Stansly 2013. Control of Asian Citrus Psyllid and Citrus Leafminer in Oranges with Foliar Sprays of Horticultural Mineral Oil, Microbial and Synthetic Insecticides. Proc. Fla. State Hort. Soc. 126: (In press, refereed) Qureshi, J. A., B. C. Kostyk and P. A. Stansly. 2012. Registered and experimental insecticides for control of ACP and citrus leafminer on mature orange trees. Proc. Fla. State Hort. Soc. 125: 92-97 (refereed). Ferrer, C. M., J. A. Qureshi and P. A. Stansly. 2012. Insecticidal control of Asian citrus psyllid: effects on secondary pests and natural enemies. Citrus Industry. 93 (4): 12-16. Qureshi, J. A., B. C. Kostyk and P. A. Stansly. 2011. Effectiveness of selective insecticides to control Asian citrus psyllid and citrus leafminer during leaf flushing. Proc. Fla. State Hort. Soc. 124: 85-89. (refereed)
Citrus leaf miner (CLM) Phyllocnistis citrella (Stainton) was established in Florida in 1993. CLM is found throughout the year but increases during the flush periods of citrus. Larvae produce mines on the young leaves between the upper and lower epidermal layers feeding on parenchymatic tissue which become foci of citrus canker lesions. The objectives of this project are: 1) Improve effectiveness of CLM management strategies through assessment of pheromone traps for monitoring CLM populations, 2) monitor insecticide susceptibility of CLM field populations subjected to intensive versus modest insecticide use, and (3) Provide recommendations for management of CLM and citrus canker disease. A trap density optimization study was initiated March 2012. Three densities of CLM pheromone traps were assessed (1 trap per acre, 1 trap per 3 acres and 1 trap per 5 acres) in a commercial grapefruit grove. A strong temporal correlation has been found between the three densities tested (. = 0.93; P < 0.001; . = 0.86; P < 0.001; . = 0.88; P < 0.001 for 1 ac ' 3 ac, 1 ac ' 5 ac and 3 ac ' 5ac respectively [Pearson Correlation Analysis]) indicating that all treatments equally describe the seasonal fluctuations of CLM populations. No significant differences were found when the cumulative number of CLM captures throughout the study was compared among treatments (F = 0.005; df = 2, 6; P = 0.95). Thus density of 1 trap per 5 ac should be as effective and more cost-effective, than the recommended density of 1 trap per ac for describing CLM phenology in large commercial blocks. A CLM colony never exposed to insecticides (susceptible colony) is being used to determine the LD50 and LD80 that will be further utilized to evaluate larvae and adult tolerance to some commonly used insecticides in CLM field populations. CLM larvae and adults from this colony are exposed during 48 h to different doses (0.01; 0.03; 0.1; 0.3; 1; 3; 10; 30; 50; 100 ppm) of the following insecticides Actara 25WG, Agri-Mek 0.15EC, Danitol, Delegate WG, Dimethoate, Intrepid 2F and Micromite 80WGS, frequently used for management of this and other citrus pests in Florida. So far, a LD50 of 2.69 (CL90: 1.00-8.6) ppm of Actara active ingredient (a.i.) has been obtained for larvae (n = 547; .2 = 1.33; d.f = 7; Heterogeneity = 0.19). The estimated LD50 and LD80 for Agri-Mek against larvae were 0.057 (CL90: 0.01-0.17) and 0.90 ppm (CL90: 0.32-6.39) respectively (n = 325; .2 = 10.37; d.f = 5; Heterogeneity = 2.07); the estimated LD50 and LD80 for Delegate against larvae were 4.49 (CL90: 1.35-10.72) and 102.39 (CL90: 37.86-620.27) ppm respectively (n = 678; .2 = 9.35; d.f = 5; Heterogeneity = 1.87); and the estimated LD50 and LD80 for Dimethoate against larvae were 4.75 (CL90: 1.67-20.08) and 513.86 ppm (CL90: 80.12-26937) respectively (n = 345; .2 = 0.32; d.f = 3; Heterogeneity = 0.11); LD50 and LD80 for Danitol. Parameters for Intrepid and Micromite larvae are being currently estimated (n = 338; n = 529; n = 267 individuals already tested respectively). Plans are to increase the number of individuals tested for each a.i. to obtain more accurate results. Similar bioassays with adults are planned for the following months.
Citrus leafminer (CLM) is a major pest of citrus, causing direct damage and increased incidence/intensity of citrus canker. Pheromone traps are useful for monitoring CLM populations and may catch thousands of moths per week. However, there is a lack of information on effective range of the traps which compromises their usefulness. Objectives of the proposed project are: (1) evaluate the effective range of standard delta sticky traps armed with CLM pheromone, (2) assess species composition of trap catches within and at defined distances from citrus groves, (3) calibrate traps with direct assessment of damage and canker incidence/intensity as tools to monitor success of CLM management programs, and (4) provide an analysis of the economic benefit of CLM management in citrus cultivars over a range of canker susceptibilities. Lure degradation studies were conducted in spring and fall 2013: Delta pheromone traps (ISCA) were dispersed in a 39ac block of Pineapple orange at Duda & Sons, Inc. located in Hendry County, Florida. Two commercial lures were tested 1) Alpha Scents (A) lure, and 2) ISCA (I) lure. Three treatments (4-week-old, 6-week-old and 8-week-old lures of each brand at the beginning of the experiment) plus a control treatment were deployed in a randomized complete block design with three replications were evaluated over a 5-6 week-period. Pheromone traps were dispensed in ~1ac plots in a central location and data collected at 1-week intervals for comparison of trap catch. Traps with lures changed on a weekly basis served as a positive control. Lure degradation was estimated for each brand by linear regression as the weekly variation on the proportion of CLM captures with respect to the control treatments. In spring, the linear regression model significantly explained lure degradation with time (A: F = 48.07; df = 1, 8 ; P = 0.0002; r2 = 0.87; I: F = 36.63; df = 1, 8, ; P = 0.0005; r2 = 0.84). The estimated time when captures were reduced to 50% with respect to the control was 9.61 weeks (CL95: 6.24-12.99) and 8.34 weeks (CL95: 4.66-12.02) for A and I respectively. In fall, a second order equation better explained the lure degradation for A whereas and linear regression better fitted data for I (A: F = 242.7; df = 2, 8 ; P < 0.0001; r2 = 0.99; I: F = 70.55; df = 1, 8, ; P < 0.0001; r2 = 0.91). The estimated time when captures were reduced to 50% with respect to the control was only of 1.24 (CL95: 0.00-6.07) weeks for A and 6.89 (CL95: 4.18-9.61) for I. The high degradation values obtained for brand A in the fall study make us think that the lures were defective. However, spring results with both brands and fall results with brand I indicate lure replacement should be done more frequently than recommended (8-12 weeks) when accurate CLM monitoring is required. Correlation studies between CLM damage and Canker severity were conducted in spring and summer flushing periods in 5 citrus commercial blocks planted with Earlygold, Grapefruit, Hamlin and Valencia varieties. CLM damage was evaluated by measuring the proportion of leaf damaged by mines in young leaves. Canker assessments were conducted approximately a month later on leaves and fruits in the same plots. Both sets of data were correlated by Pearson Correlation Analyses. A weak positive correlation between these two variables was found in spring for leaves and fruits (. = 0.38; P = 0.0399 and . = 0.35; P = 0.0572 respectively) indicating slightly higher canker incidence with greater CLM damage, but not in summer (. = -0.09; P = 0.5409 and . = 0.11; P = 0.4664 respectively). The same evaluations are currently being conducted for the last major flushing period of the year. Data collected these two seasons will provide a better understanding on how this pest and disease may be related.
The goal of this project is to determine overwintering habits of Asian citrus psyllid (ACP), including determining alternative hosts, so as to understand how to improve dormant season control strategies for ACP. The dormant season is the ‘weak link’ in the seasonal phenology of ACP and thus the time when populations of psyllids can be affected most, when targeted appropriately. In order to examine ACP population density during the winter months between 2012-13, we have sampled 40 citrus groves under differential management programs (conventional management, intermittent management, organic management and abandoned groves with no management). In the previous quarter, we reported higher ACP populations found in groves under intermittent management (such groves were defined as receiving insecticide and fertilizer treatment between 1 and 3 times per year) than the other three treatments that were examined. Analysis of additional abiotic and biotic data collected from these 40 groves over the same winter months showed little impact of surrounding landscape on ACP populations during winter months. The presence of ACP was not affected by natural or artificial borders, such as roads, residential areas or forests. Analysis of the nutrient content of leaf samples from each grove indicated that psyllid density was positively correlated with trees that show high concentration of phosphate (P) and potassium (K). Finally, we are organizing the second season of sampling results from investigations of the vertical distribution of ACP within trees during winter months. We aim to confirm the finding of the previous year: higher density of ACP associated with higher ambient temperature in the higher canopy. We will also be pursuing further sampling of potential alternative hosts of ACP to define potential alternative psyllid feeding sites that may contribute to survival during dormant periods.
Objectives of this project include: 1) scale up production of Tamarixia radiata to levels that will allow better assessment of the potential impact of augmentation on ACP populations and ultimately the spread of HLB, 2) use genetic techniques to identify parasitoids recovered from the field to demonstrate establishment and effectiveness of released strains, and 3) pass on rearing technology to both private and public sectors to encourage production and an adequate supply of these parasitoids into the future. Rearing facilities at DPI Gainesville and SWFREC Immokalee produced a total of 313,947 T. radiata during this quarter. At DPI 79,478, 51,870, 60,284 and 67,495 T. radiata were produced in colonies from South China, Pakistan, North Vietnam and Florida strain respectively, the latter previously established from Taiwan and South Vietnam. The colony at SWFREC produced another 54,820 “Florida Strain” T. radiata. Wasps from these colonies were used for research, colony maintenance and for release in conventional and organic citrus groves in Collier, Lee, Hendry, Lake, Indian River, St Lucie, Polk, and Hardee counties. Wasps were also sent to Commonwealth of Dominica. In July, parasitism by T. radiata was evaluated using 38 sentinel plants with an average of 44 nymphs per plant exposed for one week in a block of 12 acre ‘Valenica’ in a 13 acre conventional grove split into 16 plots to evaluate insecticides and nutritionals. About 7,500 parasitoids were released during that month prior to evaluation. In the untreated and nutritional treatments parasitism observed on eight (n = 18) and three (n=20 plants) plants averaged 22% (3-40%) and 20% (18-22%), respectively. Parasitism in the release and no release plots averaged 10% and 12%, respectively. Parasitism averaged 3% among feral nymphs collected from untreated (n=304) or nutritional (n=176) treatments with similar trend in August. None of the nymphs collected from insecticidal treatments (n=74) were parasitized. Psyllids averaged below 0.2 adults per tap sample so insecticides were not used during this quarter. At SWFREC, 3,000 and 2,450 Tamarixia were released in July and August, respectively. In July, parasitism averaged 28% (n= 67) in the release block compared to 0.5 % (0-3%) (n= 28-106) in no release blocks. In August, parasitism increased to 38% (n= 579) in the release block compared to 17 % (1-33%) (n= 53-255) in no release blocks. Insecticides were used in the release and no release blocks as needed. Samples collected in September are still being examined. A talk titled “Biological Control for Citrus Pest Management” was presented at Citrus Integrated Pest Management Workshop held at Indian River Research and Education Center. Sites have been selected and protocols are being finalized to evaluate mass release of Tamarixia in organic citrus at multiple locations throughout the state to determine impact on ACP.
Issue date for this grant was 13 July 2012. Objectives are: 1. Assess effects of abiotic factors (light quality, photoperiod, air flow, temperature fluctuations) on psyllid movement, 2. Evaluate physiological limits and biotic factors effecting of movement including feeding, egg load, infection status, and population density, 3. Evaluate techniques for tracking psyllid movement in the field for mark recapture studies, 4. Characterize seasonal patterns of ACP distribution and movement at different scales in the field, 5. Develop strategies to protect young trees from colonization by ACP utilizing UV reflection for repellency and insecticide treated trap crops (such as Bergera koenigii) to attract and kill. Objective 1. A bioassay was fine tuned using a wind tunnel to determine ACP response to different wind induced stimuli. ACP are marked with fluorescent powders for easy observation and released into the wind tunnel for different evaluations. ACP have been found to move up-wind, but as wind speed increases, ACP movement decreases. Further testing will be directed at determine a more complete picture of wind speed effects on movement. Objective 2. Significant progress has been made with the flight mill experiments that quantify the possible physiological limits of psyllid movement. Stelinski’s lab designed and built a new flight mill that has reduced friction compared to earlier prototypes. Thus far, they have documented and video recorded up to and exceeding 3 hours of continuous and uninterrupted flight which equates to roughly 4 miles. This sets a new record for documented Asian citrus psyllid flight capability. Such flights are now being recorded reliably and repeatedly in the lab. They are comparing the differences in flight capabilities between two color pattern morphotypes of the Asian citrus psyllid found in nature (green and grey/white). Thus far, there is strong evidence that green psyllids are more prone to longer flight distances without interruption than grey/white psyllids. Grey/white psyllids are mainly performing short and repetitive bursts of flights. They are currently setting up an experiment to investigate whether Candidatus Lineribacter infection of psyllids alters their dispersal behavior and capability. In addition, thye are developing a protocol to measure the energetic content of a psyllid (sugars, proteins, lipids) to investigate relationships between these physiological data and psyllid flight capability. Objective 3. Additional mark release trials were conducted with limited success. ACP marked with fluorescent dye have been observed using a black light at night in trees upwind of the release point and on sticky cards placed close to the release point but no ACP were found on sticky cards outside the release point. In addition the releases have not increased the extremely low levels of native ACP populations in this grove. Further attempts a mark recapture will require much greater numbers than the 2,000 released previously. Objective 4. Yellow sticky traps set at three canopy heights are giving mixed results with more ACP captures in the upper canopy in the older Charleston grove and a more even distribution at the younger and more uniform Bob Paul grove. However, the east side of the trees captures more than the west side at both locations. At both locations and also the English grove, ACP captures are greatest adjacent to a hammock or wind break. Also at Bob Paul, traps set up to assess ACP movement between insecticide sprayed and unsprayed blocks with low and high populations of ACP respectively have so far not shown significant differences in directional movement. Objective 5. A paper reporting positive results using UV reflective mulch to repel ACP the first 2 years after planting has been published in the refereed journal Pest Management Science. Subsequent results indicate that the 5 ft strip of metalized mulch is not effective on trees more than 5 ft tall. Trials were initiated to determine the impact of reflective mulch on the height of ACP flight.
The overall goal of this 3-year research project is to efficiently deliver antimicrobial molecules into citrus phloem against HLB bacteria. This quarterly (from July 2013 to Oct 2013) research continued to evaluate the effect of temperature on penetrants based on our lemon cuticle assay. The results demonstrated that penetrant value (P value) increased with temperature increase. Formulations were prepared by loading effective antimicrobial compounds into the nanoemulsion coupled with effective penetrants and applied to HLB-affected potted plants by foliar spray. One month after treatment, based on Q-PCR, Amp in nano-formulations coupled with penetrant reduced the Las bacterium to undetectable levels in new leaves, while the water control (CK1) and the Amp in water (CK2) treatments were ineffective. The bioassay will be performed in the next quarter. Water in oil nanoemulsion (W/O) was prepared using horticultural oil and sprayed on the leaf surfaces. The results indicated that application of W/O nanoemulsion captures insects, and no insects was captured in the water control. The result suggest that the W/O nanoemulsion may be applied to both control psyllids and to deliver effective antimicrobial compounds into citrus phloem for reducing ‘Candidatus Liberibacter asiaticus’. Future work will focus on the following: 1) Optimizing penetration ability of chemical compounds through isolated cuticles from different citrus varieties; 2) Evaluating of drug loading capacity using the optimized nanoemulsion formulations; 3) Optimizing the final formulations by combinations of the penetrants and high drug loading capacity formulations; 4) Evaluation of more nanoemulsion formulations combined with penetrants for controlling HLB disease and insect vectors; 5) Monitor Las bacterium in the treated Las-infected citrus by foliar spray applications.
Based on results from the previous Contest Project (CRDF#400), eleven compounds have been selected by the contest committee as candidates for further research to determine their efficacy for control of HLB based on their ability to substantially reduce the titers of the bacterium Candidatus Liberibacter in our grafted citrus assay, lack of phytotoxicity to citrus and potential for registration. After first evaluating combinations of these molecules using the graft-based chemotherapy method under a separate agreement, this project extension will evaluate these 11 compounds as control agents against the HLB bacterium individually and in combination using infected, container-grown citrus and HLB-affected scions. The objective of this project is to determine an optimum chemical formulation that may be registered for field control of HLB. In this quarter (July to Oct, 2013), 18 treatments from 11 compounds or combinations have been applied to HLB-affected potted-plants coupled with three heat treatments (40, 42 and 45 degree). All these treatments will be analyzed every 2 months for Liberibacter. The preliminary results showed that heat treatment promoted the growth of new flush from the seriously HLB-affected citrus. No bacterium was detected in the new leaves but was present in the old leaves two months after treatment with compounds coupled with the heat treatments. Four months post treatment, several treatments reduced the Las bacterium to undetectable levels both in the new and the old leaves of the containerized citrus. The research is ongoing.
We have initiated this investigation with two laboratory experiments. The aim of the first experiment was to understand how communication between citrus plants may affect psyllid host acceptance as influenced by HLB infection. We now have strong evidence that ACP are more attracted to uninfected plants exposed to volatiles from another HLB-infected citrus plant than to uninfected plants exposed to volatiles from other uninfected plants. The second experiment aims to test the effect of drought stress on the recruitment of ACP, natural enemies, and the expression of Las-inducted plant volatiles. We demonstrated that control plants infested with 50 ACP were more attractive to the parasitoid, Tamarixia radiata, than control plants without psyllids. However, under drought stress, plants infested with 50 ACP were no more attractive than uninfested, drought stressed plants. These findings were confirmed by GC-MS analysis that showed a strong decrease of volatiles emitted by drought-stressed plants even when infected by ACP. Our next objective is to test if submitting citrus plants to drought stress will lower the attractiveness of HLB-infected plants to psyllids as compared with non-stressed controls. To complement these two laboratory experiments, we are now working to identify the gene(s) involved in methyl-salyclate production in citrus. Methyl salicylate is a known attractant of ACP and our objective is to determine if this gene is up regulated under: 1) pysllid infestation 2) HLB infection and/or 3) when submitted to volatiles from infected citrus plants. Regarding the field portion of this project, we have identified groves comprised of only reset trees, as well as, groves where some resets were replanted among mature trees within a mature grove. We have monitored psyllid population densities within these groves. We have strong evidence from this year that reset trees planted in a habitat consisting of other reset trees harbored more ACP than within groves comprised of mature trees only or on citrus resets located among mature trees. In other words, psyllids were most abundant in areas containing only resets. Reset trees likely produce more flush to support higher population densities of psyllids. To better understand this observation, we plan to collect data on ambient and canopy temperatures, leaf nutrient status, and volatile production between treatments.
Our objective for this project has been to evaluate botanical compounds as repellents for Asian citrus psyllid (ACP) with the purpose of developing possible repellent formulations for use in the field. In the past quarter, we have completed a study of a new dispenser of a potential botanical insecticide. This dispenser was a hand applied product. It is based on some of our initial research with guava-based chemicals as psyllid repellents. The product is proprietary and was provided to us by ISCA Technologies as part of prototype product development. The experiment was conducted at the Water Conserv II Research and Extension site in Orange County, FL in a planting of ‘Hamlin’ oranges on Swingle rootstock. Trees were 3-4 ft in height (approximately 2.5 years old) and were planted at 12 x 25 ft. The purpose was to test the technology in young trees. All treatments were assigned randomly to 15 tree plots in a randomized complete block design replicated 5 times. There were two treatments: 1) control and 2) plots treated with SPLAT-ACP Repel Hand applied dispensers. A pre-count of all plots prior to treatment was conducted on the day prior to treatment application. Thereafter, all treatments were sampled for five weeks on a weekly basis. On each sampling date, ten terminal flush samples were collected from the interior portions of each replicate plot. Flush samples from each plot were placed in paper bags and immediately transferred to the laboratory for inspection. Flush samples from each plot were carefully examined using a stereomicroscope for pysllid nymphs. Data were collected according to the following rating scale: 0 psyllids per flush ‘ 0 1-5 psyllids per flush’1 6-10 psyllids per flush’2 11 or more psyllids per flush’3 In addition, on each sampling date, adult psyllids were counted by conducting 10 tap samples per replicate plot. For each tap sample, a tree branch was vigorously tapped with a PVC pipe directly over a horizontally placed 210 . 297 mm plastic white sheet. All Asian citrus psyllid adults found on the sheet following branch agitation were counted and recorded. Unfortunately, the results of this experiment did not result in reduced psyllid populations in the treated plots as compared with the controls. We are currently analyzing the release rates from these dispensers to determine why there was no effect on ACP population densities before we conduct a subsequent field experiment with this emerging technology. Also, we are planning experiments in more mature citrus trees.
The objective of this research is to investigate potential non-neurotoxic insecticides against Asian citrus psyllid (ACP) that could be incorporated into ACP management programs in Florida. We are especially targeting those that have shown promise against insect pests similar to ACP. Such additional tools may not only prove effective against ACP, but also could assist in ACP resistance management programs as needed tools for effective rotation of insecticides. We are specifically investigating those non-neurotoxic insecticides that have shown promise in controlling other insects pests. In the past quarter, we have evaluated methoprene in the laboratory. Methoprene is a juvenile hormone (JH) analog that acts as a growth regulator. We evaluated this compound for its ability to inhibit ACP egg hatch of eggs of various ages. We treated 0-48 hrs and 49-96 hrs aged eggs with six different concentrations of methoprene ranging from 0-320 ‘g/ml. For 0-48 hrs aged eggs, we observed egg hatch inhibitions of 14, 24, 31, 41, 65 and 84 percent for concentrations of 0, 10, 20, 40, 80 and 160 ‘g/ml, respectively. Similarly, the concentrations of 0, 10, 20, 40, 80, 160 and 320 ‘g/ml led to 13, 23, 29, 34, 39, 62 and 95 percent egg hatch inhibitions of 49-96 hrs aged eggs. These results show that treatment with methoprene successfully inhibited ACP egg hatch. These data are currently being analyzed to ascertain LD 50 and LD90 doses. We are also investigating the effect of methoprene on nymphal development. We will also investigate the effect of methoprene on adult survival, fertility and fecundity. We have also started investigations on the effectiveness of the juvenile hormone (JH) analog, Diofenolan, to inhibit the development of immature stages of ACP. The results of our research suggest that JH-analog, non-neurotoxic insecticides are effective in disrupting growth of immature stages of Asian citrus psyllid, specifically, and likely useful tools.
The objective of this study is to determine how enhanced nutrition of citrus plants may affect Asian citrus psyllid (ACP) biology. We have initiated this study with complementary field and laboratory experiments. Regarding the field trial, we are still following the Keyplex’ program. The two latest spray applications occurred in July and August. We followed ACP populations in the replicate sprayed and non-sprayed control plots from March to September. As mentioned in the previous report, from March to May we consistently observed more ACP on HLB-infected trees compared to uninfected trees. However, since June, when the ACP population increased significantly, we did not observe this difference between populations on infected and uninfected trees. Regarding the effect of Keyplex’ on infected versus non-infected plants, we observed the reverse trend on psyllid behavior: from March to May we did not observe a difference in ACP population between trees with the foliar nutrient supplement applications versus the control trees. However since June, we observed consistently more ACP on the nutrient supplemented trees than on the untreated control trees. Samples from these trees are being analyzed to see if the difference observed are statistically significant, but these results corroborate what we observed in previous laboratory experiments, where psyllids were more attracted to infected plants that were treated with the nutritional program compared to untreated, but infected control plants. Currently, we are performing an experiment to investigate the effect of nutrient sprays on HLB acquisition by ACP. Earlier, we observed that fewer ACP acquired the HLB bacterium from trees that were infected and supplemented with nutrients than from infected trees that were not supplemented after 10 days of psyllid exposure to trees in laboratory experiments. However, the results from field experiments did not corroborate these laboratory data. We did not find a significant difference between HLB acquisitions by psyllids when they were exposed to HLB-infected trees during the nymph stage on supplemented versus non-supplemented trees. We are currently analyzing the results of Candidatus Liberibacter (HLB pathogen) acquisition by ACP from field experiments after 10 and 28 days of psyllid exposure to trees. In similar laboratory experiments, we are analyzing psyllids after 28 days of exposure to trees. These experiments have compared psyllid acquisition of the HLB pathogen from infected trees that were either supplemented or not supplemented with nutritional sprays.
We have completed our annual survey of insecticide resistance in populations of Asian citrus psyllid across various growing locations throughout Florida. Five sites were evaluated in Lake Alfred, Winter Garden, Ft. Pierce, and La Belle across which 18,000 psyllids were collected and used in resistance screening assays. Insecticides at the LD50 value evaluated were carbaryl, chlorpyrifos, fenpropathrin, flupyradifurone, imidacloprid, and thiamethoxam, representing a range of chemistries available for psyllid population management. A focus on neonicotinoids was conducted to make comparisons of currently used chemistries, imidacloprid and thiamethoxam, first and second-generation, respectively, against, flupyradifurone, a new neonicotinoid, to determine base-line susceptibilities and to evaluate potential cross-resistance. An overall decrease in resistance levels was observed during this year’s survey for all insecticides tested as compared to previous surveys in 2011 and 2012. This drop may be due to better rotational practices between insecticides with different modes of action by growers, movement of psyllids from non-treated areas, or collection of psyllids from different sites than from previous years. The bottom line is that in the spring/summer of 2013, we did not observe that resistance appeared to be a significant problem in psyllid populations throughout Florida. Resistance found to be significantly higher in the field as compared with the laboratory susceptible control culture occurred for imidacloprid (1.8 fold ratio) and fenpropathrin (2.2 fold ratio) at Ft. Pierce and Lake Alfred, respectively. No other levels of resistance of statistical significance were observed in the field as compared with the susceptible laboratory population. A concomitant resistance against flupyradifurone for psyllids tested from Ft. Pierce was not observed; however, there was a trend suggesting cross-resistance. It is possible that resistance levels to neonicotinoids were too low at this site for a conclusive determination of cross-resistance between imidacloprid and the fourth-generation neonicotinoid, flupyradifurone. Additional sites are being screened for higher levels of imidacloprid resistance to identify populations to better evaluate potential cross-resistance between these insecticides. In addition, we have been developing insecticide resistant psyllid colonies against imidacloprid and flupyradifurone (and other modes of action) to address the possibility of cross-resistance directly in the laboratory.
Florida growers have reported that enhanced nutritional programs (ENPs) maintain productivity of HLB-affected trees. However, efficacy and sustainability of the nutritional approach for HLB disease management remains uncertain. Complementary studies of multiple ENPs and their individual components compared to the standard nutritional program (SNP) on nursery and field trees were initiated in 2010. ENPs did slow the development of nutrient deficiency in HLB-affected trees, but it did not prevent the development of deficiencies. The slowed nutrient deficiency was not reflected in a slowed yield decline. In both field and greenhouse trees, treatment of HLB-affected trees with ENPs resulted in a reduced fibrous root density compared to trees under the SNP. Healthy trees treated with ENPs had a slight increase in fibrous root density compared to SNP. It appears that ENP treatment of HLB-affected trees may accelerate fibrous root loss, increasing the susceptibility of the trees to stress conditions such as drought. In nursery trial, ENPs reduced the intensity of visual foliar symptoms, but not the percent of canopy with symptoms. Only on HLB affected trees, ENPs caused a reduction in total number of leaves in the canopy, although they did not change the number of new leaves produced. This suggests that ENPs induce increased leaf drop. Based on symptom observations, it is likely that the leaf drop is of leaves that would have expressed strong symptoms. Combined, these results suggest that ENPs are masking HLB damage to the tree by decreasing the percentage of canopy with easily visible yellowing, but not improving the biomass or health of the tree. A manuscript describing the results of this project has been submitted to a peer-reviewed journal and is currently under review for publication.
The objectives of this project were to screen insecticidal peptides for efficacy against the Asian citrus psyllid (ACP) citrus leafminer, brown citrus aphid (BCA), and T. radiata and to determine the lethal and sublethal effects of antimicrobial peptides on ACP and their associated microorganisms, including Candidatus Liberibacter asiaticus (CLas). A citrus tristeza virus (CTV) vector system was used to express candidate insecticidal peptides in plants tissue. After screening a range of insecticidal peptides against ACP in artificial feeding bioassays, four insecticidal peptides (A-D) were selected and transformed into citrus tristeza virus (CTV) vectors for further evaluation against citrus pests. For each insect species, we evaluated life history parameters (fecundity, nymph development, and survival) and feeding behavior. The effect of CTV-expressed peptides on ACP host preference and CLas titer were also evaluated in laboratory bioassays. We have identified one peptide that, when expressed in Valencia in a citrus tristeza virus-based expression vector system, elicits negative responses from two phloem-feeding citrus pests. Additionally, we have demonstrated that all peptides evaluated disrupt various aspects of ACP biology and behavior, including feeding and settling. Reductions in feeding and ACP CLas titer in response to peptide presence suggests that use of the CTV-peptide expression system may provide an effective tool for management of CLas transmission as part of an integrated pest management program.
(863) 956-8817
(863) 956-5894
700 Experiment Station Road
Lake Alfred, FL 33850
Email Us
