March 31, 2013 Update: Activities of the CHMA program assistant (Brandon Page) Jan 1 – March 31 2013: During this reporting period, the CHMA assistant provided support to the CHMA effort by attending various local CHMA meetings as well as statewide meetings. Specifically, Mr. Page attended 14 meetings where he either gave an oral presentation, setup CHMA displays such as posters, or participated in group discussions. Venues included Citrus show in Ft. Pierce, ConservII management meeting, IRCHLB in Orlando, South Lake / West Orange CHMA meeting, Gulf CHMA meeting (2x), Florida Southern College, Futch’s Citrus Production school, Mid-Florida Citrus Foundation Field Day, Hardee CHMA meeting, IRCHLB grower day at CREC, Ft. Meade ALturas CHMA meeting, North and Central Polk Co CHMAs meeting, and the Volusia CHMA meeting. In addition to attending meetings, daily updates were made to the CHMA website based on communication with CHMA grower leaders. Work also continued on the mapping program that went live online at the end of December 2012. A considerable amount of time has also been spent working out the bugs in the program and working with the programmers to enhance the program with new features not yet available online.
March 2013 update: Field trials conducted to determine the true longevity of pesticide applications were completed this spring. The goal of the project was to use caged psyllids on treated trees to assess how long pesticide residues remain active on the foliage of trees killing adult psyllid fly-ins. This is in contrast to the manner we normally evaluate pesticide products by spraying out products and evaluating how long psyllid populations remain below the untreated control. Such an evaluation really is only a measure of how long it takes psyllids to reinfest from surrounding areas and thus can be influenced by the surrounding psyllid population levels. In this study, we examined three pesticide active ingredients, dimethoate, Danitol (fenpropathrin) and Admire (imidacloprid applied foliarly). These products were applied at label rates during the months of January, April, September and November. The products were applied during these months to represent weather extremes at different times of the year when growers are making their pesticide applications. On each application date, 24 hrs after sprays were applied, adult psyllids were caged on the treated trees. After 7 days had passed, the cages were removed to assess psyllid mortality and new cages containing alive psyllids were then cages back on the same tree in order to continue the evaluations of duration of pesticidal efficacy. The results showed that 1 day after application, all pesticide residues on leaves provided near 100% control of adult psyllids with one exception. In september, high rainfall occurred approximately 12 hrs after the treatments were applied resulting in less than 60% control 24 hrs after the applications were made. This shows that despite the fact that the products had time to dry after applied, rains that are typical during the florida rainy season can negatively influence pesticide effectiveness. By 7 days after application, percent mortality across all treatments was less than 60% in most instances with even greater reductions observed following periods of heavy rain. Time of year did not have an impact on pesticide efficacy, dispelling the notion that pyrethroids work better in the winter and organophosphates provide better control in the summer. These results suggest that it is more important to choose a product for psyllid control based on rotation from previous MOA used rather than trying to use only pyrethroids in the winter and OPs in the summer. Additionally, these results show that growers are not likely to obtain as long a duration of psyllid control as they previously thought possible. This is likely best overcome through coordination of sprays through the CHMA program.
This research seeks to determine whether young trees infected with CLas and displaying typical HLB symptoms can be brought to maturity and produce an economically viable yield. This will be achieved by managing a 58 acre grove of 3-year-old ‘Valencia’ / Kuharske Carrizo trees using a combination of three different foliar and three different ground applied nutritional programs. Factorial AxB treatments consist of A) ground-applied: 1) Liquid/dry+Ca (BHG standard), 2) Liquid+Ca, 3) Liquid/dry-Ca B) foliar-applied: 1) BHG standard-Ca, 2) BHG standard+Ca, 3) “Prescription”(+Ca). The prescription treatment was designed to be dynamic, customized for optimization, with feedback based on frequent leaf tissue analyses, visual symptoms, and the growth of the tree canopies and yield. There are six replications of treatments, with two being pure replications. The grove continues to look good and actually improve, despite the nearly 100% HLB incidence. Foliation of canopies is dense, and leaf color going into late Fall season was a healthy green. Tree sizes (heights and total canopy volumes) were measured and analyzed on 1 November 2013, as follows: FOLIAR FERT Tree Ht(in) STD-Ca STD+Ca Prescrip SOIL FERT Liq/Dry 89.6 87.0 93.8 Liq 89.4 82.5 97.0 Liq/Dry-Ca 90.0 86.6 86.3 FOLIAR FERT Canopy vol(ft3) STD-Ca STD+Ca Prescrip SOIL FERT Liq/Dry 287 239 306 Liq 268 207 324 Liq/Dry-Ca 286 242 237 Both the tree height and canopy volume means showed non-significant (NS) differences between treatments, which agrees with the visual observations made in the grove. Leaf samples were collected in December 10, 2013 and the results of nutrient analysis of the leaf tissue were NS except for B and S. All the different fertilizer strategies chosen for testing in this block appear to be working equally well. The slightly adverse effects of the +Ca foliar sprays on canopy size and fruit yield in 2012/13 appear to be corrected in 2013/14.
Entomopathogenic nematodes: Amending soils to increase biological control of insect pests Processed the autumn soil samples from Schumann ACPS trial in Auburndale and new trial in Bartow in which sulfur is a treatment to reduce pH from near neutral to near 5.0 and determine effect on Paenibacillus sp. infestation of Steinernema diaprepresi and on the population density of the nematode. Briefly, both trials revealed remarkable similarity in quantitative relationships (regression equation) between population density of the bacterium and the nematode. Relationship is significantly positive, but infestation rate (bacteria spores per nematode) decreases with population density of the nematode. Across 4 treatments and 40 plots, numbers of S. diaprepesi are inversely correlated with soil pH (P<0.001), supporting the relationship measured in the Auburndale trial. However, the numbers of nematode in plots treated with sulfur do not yet differ from those in other treatments. If numbers do change over time it will be the first known example of a specific agronomic practice that can be exploited to conserve services provided by entomopathogenic nematodes. Wrote 'New citriculture system suppresses entomopathogenic nematodes and biological control of subterranean herbivores' Campos-Herrera, R., Pathak, E., El-Borai, F., Schumann, A., Abd-Elgawad, M.M., Duncan, L.W. for publication in Biological Control. Plant parasitic Nematodes: Characterizing a new nematode pest and the prevalence of resistance breaking populations of the citrus nematode. Continued sampling and processing citrus soil from Indian River, St. Lucie counties. Identified sites for chemical trials to begin in February 2013. Used newly developed PCR primers and Taqman probes to confirm identities of 4 populations of putative X. citricolum and X. laevistriatum. All positive for latter species, none for former. This raises questions about validity of these species. Sampled 4 sites identified in original publication as sources for these populations. Dagger nematodes from these sites are being characterized for morphology and ITS and D2/D3 region DNA sequences. These samples should be adequate to validate or invalidate the current taxonomy in this group of citrus parasites.
Dec 31 2012 The objective of this project is to investigate three questions: 1) whether HLB symptoms or boron/zinc deficiencies alone affect how ACP responds to citrus; 2) whether feeding patterns by adults, length and location of feeding, are altered by HLB infection or boron/zinc deficiencies; and 3) whether different strains of Ca. Liberibacter asiaticus (Las) differentially affect the response of ACP to citrus. In other pathogen/host/vectors systems, such as that with Ca. Phytoplasma mali and Cacopsylla picta (the apple psyllid), the pathogen manipulates the plant host metabolism so that diseased plants become more attractive to the psyllid vector, thereby spreading the pathogen more rapidly than if no plant host manipulation occurred. Since nutrient deficiencies are often associated with HLB in citrus, we wished to confirm that the reported attraction of Diaphorina citri to HLB symptomatic plants over uninfected plants was due to changes in host metabolism by the pathogen rather than physiological changes due to poor nutrition. Boron deficient trees suddenly became too deficient and lost all of their leaves. Have adjusted boron and zinc levels up very slightly to keep the trees deficient but still keep the leaves. The trees are just starting to flush. Lights were installed in the greenhouse to stimulate as much flush as possible.
Dec 31 2012 The objective of this project was to investigate three questions: 1) what is the seasonal pattern of Ca. Liberibacter asiaticus (Las) prevalence in leaf tissue on a grove scale; 2) what are the flushing patterns of citrus and do the flushing patterns affect the prevalence of Las in Diaphorina citri or citrus leaves; and 3) what is the prevalence of Diaphorina citri carrying Las on a grove scale and how does it compare the results from the citrus trees in the same grove. In 2008 and 2009 Ebert and Rogers demonstrated that the prevalence of Las in the Asian citrus psyllid (ACP) varied seasonally but the pattern between seasons was not consistent. It was suggested that perhaps the reason for the differences between the years related to the flushing patterns of citrus and the prevalence of the bacterium in the leaves where ACPs are feeding. This project aims to determine if there is a relationship between the frequency of disease on branches and ACPs. Sample collection of psyllids, phenology and plants has continued throughout the fall and into the winter. Psyllids have been difficult to collect in the last 6 months, likely due to area wide psyllid control. This is a positive result for the industry but has made this project more complicated. Flush has occurred early in 2013 and a considerable amount was recorded over the new year.
The objective of this project was to investigate three questions: 1) How long does a leaf needs to be infected by Guignardia citricarpa before ascospore production can be initiated; 2) How does infection and colonization of leaves by Guignardia citricarpa occur and potentially showing how pseudothecia, the sexual spore producing structures, are produced; and 3) what is the interaction between the common twig colonizing pathogen Diaporthe citri and the black spot pathogen Guignardia citricarpa and whether they can co-exist to successfully sporulate on dead twigs. The graduate student, Nan-Yi Wang, whose Ph.D. project this is, continues his studies in Gainesville this term and is making good progress in his classes. He is also conducting research while in Gainesville. With the sequence we have confirmed the one end of a mating gene cluster but second end has been elusive. We realized a mistake made looking for a gene that is likely not present on the 2nd end of the mating gene and have changed our strategy. To add to the confusion there is a close gene homologue to our initial target gene in the genome. All of our attempts to walk the missing sequence between the known genes of the mating cluster and this gene homologue failed but we now understand why. We have not been able to purify the genetic background of the gfp label citricarpa. It may be a promoter problem that we cannot get fluorescence in the conidia. We are attempting a new transformation technique with new promoters. Preliminary greenhouse experiments have been initiated.
We have discovered two compounds produced from degraded primary citrus volatiles that have been found to stimulate the antennae of both male and female Asian citrus psyllids. Constitutive (primary) volatiles from host plants have long been known to produce both antennal and behavioral responses in various insect species. Induced (secondary) plant volatiles emanating from plants that have been damaged by insect feeding or microbial infestations can also elicit antennal responses and affect behavior of host insects and their parasites and predators. Our discovery of compounds formed from degraded primary citrus volatiles that produce antennal responses in the Asian citrus psyllid illuminates a new area of research previously unknown in chemical ecology. We are investigating behavioral responses to these compounds using several methodologies in both the laboratory and the field. We are now collaborating more closely with Dr. Joe Patt who was recently transferred to our laboratory from Texas. Together, we are exploring application of innovative bioassays to test behavioral response of ACP to volatile compounds we have identified by electroantennography. Additionally, we are investigating dosage ranges of various constitutive citrus volatiles that have been found to be stimulatory to the antennae at dosage levels higher than we might normally test in insect groups unrelated to the psyllid. Psyllid antennae have many fewer olfactory receptors when compared to other more thoroughly investigated insect groups such as moths and beetles and thus may require higher levels of stimulation than what is expected.
Yield and juice data from the fifth year (2008-2012) of the replicated Hamlin trial on station at SWFREC evaluating the Boyd cocktail ingredients shows that the trees are growing well and maintaining production. In spite of the 2012 January 4 freeze causing delayed spring growth and bloom, the drought with only 38 inches of rain (53 normal) in Immokalee in 2012, and the fall fruit drop experienced industry wide, the 7 to 8 foot tall trees produced above 2 boxes per tree. The highest yielding treatment in each of the past 5 years has been treatment 2 (Boyd cocktail less SARs) with 2.5 boxes/tree. Not significantly different are treatments containing foliar applied micro-nutrients (Mg, Mn, Zn, Mo, B,) with a macro source of N and K as DKP + KNO3, and a Phosphite. Each year since 2008 the yield has increased in this trial. Treatments which do not contain the above foliar applied nutrients have been among the lower yielding trees showing nutrient deficiencies and considerable symptomatic leaves of HLB. Juice quality was down this year when fruit was harvested late December. Juice content, acid, and Brix were low and ratio was good. The 30-acre Valencia trial in a commercial grove will be harvested in April. We are well into the 5th year of a replicated experiment in a 12-acre commercial block of 8-year-old ‘Valencia’ oranges on ‘Swingle’ to test effects two factors: (1) micro-nutrients + systemic acquired resistance inducers, and (2) Asian citrus psyllid (ACP) chemical control on ACP populations on Can. Libericacter asiaticus (CLas) titer, and plant yield. Since our last report we applied Delegate (5oz/ac + 1% Oil) and Danitol (16oz/ac + 1% v/v 435 Oil) on insecticide plots (8 Nov, 5 Dec, respectively). Psyllid populations for Insecticide treatments exceeded the 0.20 threshold on 3 occasions (1, 15, 30 Nov), which included two dates following the Delegate application. Insecticide treatments resulted in significantly (P< 0.05) fewer adult ACP than non-insecticide treatments on all dates sampled. All treatments resulted in significantly (P < 0.05) fewer adult ACP than the untreated control on dates 15, 30 Nov. Only in insecticide treated plots did we see significantly fewer ACP than the control on 18 Oct, 1 Nov, and 14, 26 Dec. Mature trees and resets planted (June 2010) were tested for HLB detection (24 July). While there was no significant (P < 0.05) treatment effect on percentage HLB for mature trees, Insecticide-only treated resets had significantly less (P < 0.05) HLB (0.94'0.04 SEM) than the other treatments. There were no significant differences in Ct values for mature (Mean range 22.59 ' 24.65) and reset (Mean range 29.20 ' 31.97) trees. October HLB results are still pending, and another collection date is scheduled for next week. During the past 3 months phloem studies were done on nutrient treated HLB trees at both the Southwest Research and Education Center and at the Orange Hammock in Felda, Florida. Studies included both cytology work as well as fluorescent dye translocation studies to determine if new phloem is being produced in those trees treated with additional nutrient materials. Visually the fluorescent dye translocation studies again verified that phloem uptake was better in the trees that received the supplemental nutrient materials. That is that the fluorescent dye was not translocated from the application zone with untreated leaves but was in the treated leaves. Microtiter plate assays again were used to quantify the amount of dye retained (or translocated) in the sites. Assays did not agree with the visual assessments during this time period due to sampling procedures and seasonal variability. The procedures have now been revised.
During fall 2012, we monitored 4 trials where pheromone was deployed to suppress citrus leafminer in collaboration with ISCA and grove managers to address pheromone carrier, timing, deployment pattern, and efficacy of mating disruption on leaf damage caused by citrus leafminer. 1. Winter and spring application of pheromone (2013). Cooperator: Packers of Indian River. Winter and spring pheromone applications in a factorial design with split plots in 4 blocks will be treated with rubber dispensers loaded with triene (834 mg/ha) in winter (February) and spring (April). Main plots (6.4 ha) and subplots (3.2 ha) will be 35% larger than last year. Trap catch and leaf mining will be evaluated. 2. Trials 1-2: Solid dispensers, Golden River Fruit Co., St. Lucie Co. We monitored traps in 0.14 ha plots treated with rubber dispensers (318 per ha) loaded with ‘natural’ 3:1 blend or triene only. Trap catch disruption was >95% for 18 wks. There were no differences in CLM infestation suggesting plots were too small for flush evaluation. A 68 ha plot was treated with rubber dispensers loaded with natural blend on 24 Aug. Trap catch disruption was >95% for 18 wks. There were no differences in infestation at 8 wks suggesting that female moths arrived in treated plots already mated, or moths mated in treated plot despite strong trap catch disruption. 3. Trial 3: Large plot rubber dispensers, Packers of Indian River, St. Lucie Co. An experiment was started in Sept. to compare disruption in 0.87 ha plots treated with rubber dispensers containing ‘natural’ 3:1 blend (330 dispensers/ha) or untreated. Plots were 4 times longer than wide. Trap catch disruption was >98% for 15 weeks. As above, there were no differences in CLM infestation. 4. Trial 4: Large plot rubber dispensers, TRB Groves, Charlotte Co. We continued monitoring a grower validation trial treated on 20-23 August (42 ha) with solid rubber dispensers loaded with pheromone (natural blend). Trap catch disruption was >99% for 11 weeks. 5. Manuscript near completion. We are near completion of a manuscript: ‘Attraction of a Native Florida Leafminer, Phyllocnistis insignis (Lepidoptera: Gracillariidae), to Pheromone of an Invasive Citrus Leafminer, P. citrella: Evidence for Mating Disruption of a Native Nontarget Species.’ The manuscript shows that a native leafminer is influenced in groves treated with citrus leafminer pheromone which in turn could influence populations of citrus leafminer if these two species share common natural enemies.
The incidence of citrus canker has been increasing in Florida due in part to increased pressure from citrus leafminer (CLM). It is likely that broad-spectrum insecticides for ACP management have impacted natural enemies of CLM leading to its rebound as a pest. The objectives of this study are: (1) Assess the use of pheromone traps for monitoring CLM populations, and development of a preliminary degree-day model, (2) evaluate effectiveness of early season and aerial applications to reduce CLM and canker, (3). Obtain baseline susceptibility to key insecticides, and (4) Use a diagnostic dose to monitor resistance in field populations of CLM exposed to intensive versus modest insecticide use. Objective 1: We have been monitoring adult CLM weekly with Delta pheromone traps under 4 management scenarios: 1) sprayed at peak trap capture using different trap densities, 2) sprayed based an ACP threshold, (3) biweekly low volume (LV) sprays with horticultural spray oil (HMO) and, 4) untreated control. CLM damage is being assessed using a modified Horsfall-Barratt scale 1 to 8) and canker by percent incidence for individual trees, number of areas or ‘hits’ present in a tree, and proportion of diseased fruit. In a replicated trial in a 10 acre block of mature ‘Valencia’, significantly less leafminer damage was seen in Oct with LV-HMO (HB rating 2.25’0.13) than the grower standard (GS, 2.60’0.11) or UTC (2.60’0.14). In addition, the proportion of fruit with canker was significantly less in oil-treated plots (0.02’0.01) than the GS plots (0.04’0.01) demonstrating that oil was managing CLM and canker as well as GS. In another replicated trial evaluating results of threshold based insecticidal control of ACP, (P<0.05) fewer CLM were seen in the Oct 2012 flush on trees treated with insecticide compared to trees treated only with foliar nutrition. Untreated trees also had significantly less incidence for canker than the other treatments which corresponded to less flush. In a replicated trial on canker-susceptible 'Earlygold' orange, lower (P < 0.05) canker ratings (0.94'0.02 on a 1-8 scale) were seen in plots sprayed at a 0.2 ACP/tap threshold than the 0.7 threshold (1.08'0.10). In another experiment traps were placed in grapefruit at 1, 3 or 5/ac. More captures at lower densities would indicate greater effective range. We did find more moths (P < 0.05) in traps placed at 5ac compared to 3ac, although during Oct (11, 18, 25), there were more captures at 1 trap/ac than at 5 traps/ac indicating season variation in the effective range of the traps. Pheromone traps have also been deployed in citrus groves and non-citrus areas determine optimal spatial scale for trap distribution and to see if non-target species are captured. Collections of moths (755) and host plants (11) were made at 3 known distances from citrus groves in a State Forest. Moths and photos of mined host plants (2011, 2012) were sent to the Kawahara lab in Gainesville for identification. The CLM phenology and temperature data is currently being analyzed to determine degree days for growing season peak flights and generation time to develop the degree day model. Objective 2: Trees sprayed at peak trap capture had significantly lower incidence (P < 0.05) of canker, CLM damage was less compared with trees sprayed with Delegate earlier (1.14'0.05) or later (1.14'0.04). Objectives 3 and 4: CLM colonies are being rebuilt after a series of crashes in preparation for the baseline susceptibility studies to begin (Feb) followed by field testing of a diagnostic dose.
December 2012 Update: Activities of the CHMA program assistant (Brandon Page) Oct-Dec 2012: During this reporting period, the CHMA assistant provided support to the CHMA effort by attending various local CHMA meetings as well as statewide meetings. Specifically, Mr. Page attended nine (6) local meetings of growers or CHMAs. The locations or CHMA meetings during this reporting period inlcuded: Ft. Meade/Alturas CHMA, Hardee CHMA (2 separate meetings), NE Desoto CHMA, CREC Field day, and Hillbillies. Mr. Page also attended and participated in 2 regional meetings by representing the CHMA program at SunBelt Ag Expo (Moultrie GA) and the FL Ag Show (Balm). In addition to attending meetings, daily updates were made to the CHMA website based on communication with CHMA grower leaders. Work also continued on the mapping program that will generate TRS maps of psyllid counts for each CHMA. The program was completed in late December and after some additional testing will be made available online through the CHMA website in early 2013.
December 2012 update: In the multi-year field study designed to determine the effects of different pesticide management strategies on the ability to bring young trees into production, we previously reported that during the first 12 months after planting, the HLB infection rate in the majority of plots remained low. By treatment (season-long program), the HLB infection rates (from least to greatest) were as follows: rotation of soil-applied neonics + foliar insecticides = 0% HLB, rotation of soil-applied neonics + foliar applications of kaolin = 0% HLB, foliar applications of Kaolin only = 1.3% HLB, foliar insecticide applications only = 2.5% HLB, untreated control plots = 3.8% HLB, and soil-applied neonicotinoid applications only = 11.3%. The increased rate of HLB in the neonic only plots corresponded with a failure to applications to control psyllid populations. Resistance assays conducted with psyllids collected from these plots yielded a resistance ratio to neonicotinoids as high as RR=126. Coincident with the finding of localized resistance in these plots, the psyllid populations increased across the majority of plots and ultimately were controlled below detectable levels with the application of a broad-spectrum pyrethroid insecticide. Since that time, no additional product failures have been observed indicating that the resistant psyllid population had been successfully eliminated. However, the 2 month window of failed control across the entire block ultimately lead to a dramatic increase in HLB incidence across all treatments as later determined by PCR analysis of leaf samples collected from each tree during the 15 and 18 month HLB evaluations. By the 18 month HLB evaluations, the HLB infection rates (from least to greatest) were as follows: Kaolin only = 31% HLB, rotation of soil-applied neonics + foliar applications of kaolin = 35% HLB, soil-applied neonicotinoid applications only = 40% HLB, rotation of soil-applied neonics + foliar insecticides = 43% HLB, untreated control plots = 52% HLB,and foliar insecticide applications only = 53% HLB. While these results may appear discouraging, they demonstrate that if proper product rotation is followed and thus resistance is prevented, HLB infection rates in young trees can be maintained at low levels. A spatial analysis of HLB infection in relation to proximity to the initial plots where resistance development was documented has shown a significant trend in HLB infection rate by treatment applied. With the resistant psyllid population eliminated, we will continue to follow disease incidence in this grove to determine how much additional disease spread occurs, particularly with respect to those trees not yet infected.
The goal of this project is to determine the 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. We have completed a detailed survey of ACP presence in Lake Kissimmee State Park (Polk Country, FL), where we captured ACP consistently throughout a season. In this forest, occurrence of citrus is particularly rare (only three tangerine trees), and no Rutaceae were found in the trapping locations or at nearby (‘500 m) areas to where ACP were captured. In addition to trap capture data, complementary laboratory no-choice feeding bioassays for ACP performed using Red bay, gallberry, and blueberry. These were selected as possible alternative hosts, given their presence in locations where ACP were captured. The results suggest that ACP may have a wider alternative host feeding range than previously thought, which may allow for significant dispersal even through dense forests in Florida up to 2.3 km from large-area plantings of citrus. For our next set of experiments, we have acquired a new, industrial-strength vacuum system for collecting insects in the field. During the next two months, we will sample two locations comprised of commercial citrus. Each will be divided into two comparison plots: one oriented north-south and the other east-west. We will sample the citrus canopy at three different heights and orientations at the four cardinals directions. In addition, we will employ a truck-mounted platform to sample the very tops of the canopies of citrus trees. Our objective is describe the two dimensional distribution of ACP within commercial grown citrus trees during winter. Hobo data loggers will be placed at these various locations to correlate temperature and relative humidity with ACP distribution. Another aspect of this project is to determine the population density (fluctuations) of ACP seasonally by monthly sampling of 10 citrus groves with varying management input (conventional, organic and abandoned) in order to understand the overwintering preference of ACP. Our results to date indicate that there is significant variability in the number of ACP occurring within these three different management scenarios. Our currently ongoing objective is to correlate these distribution differences among the various treatments with specific biotic and abiotic factors such as: citrus leaf nutrient analysis, descriptive habitat analysis (plant and insect biodiversity indexes), and ACP fitness analysis (survival and fecundity studies). These additional data should help us understand why differing population densities of ACP observed in the treatments we are investigating do not always correlate well with ACP management practices.
Previously, we have reported efficacy results for two insecticidal peptides expressed by the CTV vector used in bioassays with ACP and the brown citrus aphid (BCA). During those experiments, we observed significant variation in psyllid responses among plants expressing the same peptide. We expect that this variation may be due to differential expression of the peptide genes among the transformed plants; therefore,we are now developing peptide-specific qPCR assays to quantify peptide gene expression between and within plants. Once qPCR screening is complete, psyllid survival will be assessed in response to plant peptide titer. Since our last report, two new peptides have been identified in artificial feeding assays as effective in reducing the fitness of Asian citrus psyllids (ACP) by reducing insect survival and fecundity. These peptides have been introduced into the previously described CTV vector and introduced into citrus. During the past quarter, the majority of plants graft inoculated with these peptides, 85 and 100% respectively, have been identified as positive for the peptide-vector constructs during screening by enzyme-linked immunosorbant assays (ELISA). Following the completion of qPCR assays for these peptides, bioassays will be completed to assess the survival, fecundity, and development of ACP and BCA, and settling preference and feeding behavior of ACP.
(863) 956-8817
(863) 956-5894
700 Experiment Station Road
Lake Alfred, FL 33850
Email Us
