Studies show that predators (predaceous insects and spiders) form an important source of mortality for the Asian Citrus Psyllid (ACP) in Florida, much more important than the parasitoid Tamarixia radiata. In California we do not know if predators form an important mortality source as well, nor do we know which predators are involved. This project aims at determining the relative importance of different predator species as a mortality source for ACP by identifying which predators have fed on ACP. To determine if a predator has fed on ACP we will use PCR techniques to detect if ACP DNA is present in the gut of the predator. The complex of species that feed on ACP during the day may differ from that feeding on ACP at night, consequently we sample for predators both during the day and at night. This is the first reporting period for this project and during this period we have sequenced several genes of the ACP to determine their suitability for developing probes for ACP DNA detection in predator guts. Several DNA regions have been identified as potentially suitable for primer and probe development, and primers have been designed. They remain to be tested for specificity and ability to detect low DNA concentrations. Day time samples have been taken at two different dates, on one of these dates both an early night time sample and an early morning sample have been taken to collect night active predators. Ultimately, the goal of this project is to identify the relative importance of different predator species as a mortality source for ACP and to either develop cultural practices that may increase the populations of these predators in the field and/or to identify species that may be mass reared to help control ACP populations. To quantify the overall importance of predators for the control of ACP populations exclusion experiments are done. In these experiments we determine ACP mortality on terminal twigs that are completely protected from predation by enclosing the twig in a mesh bag, partially protected from predation by enclosing them in an open bag, or left exposed to predation by leaving the twig without enclosure. Different survival rates of ACP populations under these different experimental conditions will give an indication of the relative impact of predation on ACP population growth.
A method was developed and used to show that topical application of salivary sheath inhibitors to the surface of citrus leaves can block Asian citrus psyllids (ACP) from forming intact salivary sheaths and thus inhibit direct feeding on the citrus phloem. Because the phloem is the location of the Candidatus Liberibacter asiaticus (CLas) bacterium, it has been our hypothesis that deploying a ACP control strategy that prevents the ACP from reaching the phloem will prevent the ACP from either acquiring or transmitting the CLas. Also, manuscript was accepted in PLOS ONE describing methods used to produce pure salivary sheaths from a number of salivary sheath forming plant feeding hemipteran insects. The advantage of this method over previously used methods is that it allows analysis of specific sheath components (i.e. flang and primary shaft) without contamination of any other components typically present in diet and or plant tissues. This method is being used to provide structural confirmation to support the compositional data already obtained for ACP formed sheaths.
Our objective for this project has been to evaluate botanically derived compounds as potential repellents for practical application against Asian citrus psyllid (ACP) as part of potential integrated pest management strategies. In previous quarters, we evaluated five botanical oils as repellents for ACP. Of the five, only one, fir oil, was repellent in laboratory bioassays. We submitted a manuscript recently for scientific peer review, based on this research (to the Journal of Pest Science). In this manuscript, we reported data from: (1) olfactometer bioassays indicating that fir oil is repellent to ACP and that clove and camphor oils are attractive to ACP, and (2) laboratory settling experiments with fir oil treated plants, and (3) field trapping using baited yellow sticky cards. Based on these results, a new proprietary release device was developed by a commercial partner that we will be testing in the next quarter. This device releases fir oil at a controlled rate and we will be testing whether this rate has practical value in the field. We have already received these dispensers and we will initiate the experiment as soon as trees begin their next large flushing cycle to ensure there will be an adequate number of psyllids for a stringent test. In addition to what we have reported previously, we have continued experimentation towards identifying further botanical repellents. Since fir oil was repellent in laboratory bioassays, we decided to test turpentine as a less expensive alternative. Surprisingly, our settling bioassays with turpentine treated vs. control seedlings showed that the ACP may have a preference for settling on plants treated with turpentine odor (57% on turpentine treated seedlings and 43% on control seedlings). Since fir oil treatments were much more effective at repelling ACP than turpentine treatments, we will be focusing on this treatment in the subsequent field studies.
Key unknowns about Asian citrus psyllid biology in Florida: Overwintering sites and alternative hosts The goal of this project is to determine overwintering habits/sites 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. Recently, we submitted an article regarding our survey of Lake Kissimmee State Park to Florida Entomologist it has been accepted. From January to March, we performed extensive sampling with a high-powered insect vacuum system to determine ACP overwintering habits. Briefly, we sampled two areas of citrus production that were divided into two plots: one oriented north-south and the other east-west. For each plot, we sampled the citrus canopy at three different heights and four cardinals orientations. The purpose was to develop a two dimensional picture of ACP distribution within citrus groves during winter. Environmental data loggers were placed at these different locations to correlate temperature and relative humidity data with ACP distribution. Moreover, we collected and analyzed nutrient content of leaves at each location. During the next few months we will analyze the data and develop a scientific article to report this information. An additional aspect of this project is to assess how management of citrus groves has an impact on ACP population dynamics during winter months. During the 2012/13 winter, we sampled 40 citrus groves with various management programs (conventional, poorly managed, organic and abandoned) to understand the overwintering population dynamics of ACP over a broad range of grove types throughout Florida. Our results show that significantly more ACP are found in poorly managed groves than in groves under any other management. Our current objective is to correlate these discrete ACP distributions with certain biotic and abiotic data such as: citrus leaf nutrient analysis, landscape characteristics, soil data, meteorological data and ACP fitness analysis (survival and fecundity studies). Furthermore, we will compare these findings with ACP abundance data collected over 2 winter seasons from 40 more groves in Florida. These data will yield clues as to potential ‘winter reservoir groves’ that may require more intense management over winter months in order to reduce the population growth of ACP in the spring season.
The goal of this project is to identify insecticidal or antimicrobial peptides with efficacy against phloem-feeding citrus pests, including the Asian citrus psyllid (ACP). Previously, we reported that citrus plants expressing Peptide B showed promise in terms of deterring feeding by ACP, but that only four plants had been evaluated at the time of reporting. During this reporting cycle, we have completed additional replicates that corroborate our previous findings. Additionally, the final peptide to be tested, Peptide D, was evaluated in detached leaf assays and it was found to be the most efficacious out of the four peptides at significantly deterring feeding by adult ACP. Our results also showed that by 48 hours, the feeding behavior of ACP had returned to normal levels when insects fed on Peptide A, while Peptides B and D continued to deter feeding through 72 hours. Future experiments will examine protective effects beyond the 72 hour time point with the most promising peptides. In a preliminary study, we observed that when Asian citrus psyllids harboring Candidatus Liberibacter asiaticus (Las) at rates between 20-80% were held on plants expressing Peptides A, B or C, there was a reduction in the percentage of Las-positive insects after 15 and 30 days post-exposure to the plants, as well as, a reduction in the percentage of infected offspring. Plants necessary to set up a fully replicated experiment to investigate the potential phenomenon of peptide-conferred protection against Las have been grafted with CTV-peptide constructs, and once they have been screened and test positive for CTV expression, assays will be started to investigate these findings. Meanwhile, we have developed quantitative PCR primers for three of the four peptides under investigation in order to correlated psyllid responses to peptide expression in planta. This information will provide important information as to the potential for consistent management of Las transmission by ACP with the most promising peptides.
Biorational, non-neurotoxic insecticides play an important role in integrated pest management given that they typically target a narrower range of species as compared to conventional, broad-spectrum, neurotoxic insecticides. Also, non-neurotoxic insecticides often cause lower levels of toxicity to beneficial arthropods, including parasitic wasps and ladybird beetles, than conventional insecticides. During this report cycle, we have begun evaluation of three new compounds against Asian citrus psyllid (ACP) that fall under the non-neurotoxic category: novaluron, concanavalin A (jack bean lectin), and L-canavanine. Initial experiments with the chitin biosynthesis inhibitor, novaluron, indicate that this insecticide may hold potential as a control agent against ACP by inducing sub-lethal effects on the insect, including reduced egg hatch and reduced adult emergence. Based on these initial studies, Rimon’, the commercial blend of novaluron, is being evaluated at three field rates recommended by Chemtura for testing: 10, 15 and 20 fl oz. These rates are based on efficacy against other Hemipteran species in other fruit crops and on our initial experiments. This insecticide will be evaluated to determine the effect on egg hatch, adult emergence, and fecundity at these three rates. The other compounds under current evaluation, concanavalin A and L-canavanine, are being evaluated against adult ACP to determine feeding deterrence and effects on ACP mortality. Effects on feeding deterrence and mortality have been observed for other related insect species. Initial experiments suggest that L-canavanine, a non-proteinogenic amino acid, may deter feeding of ACP on citrus. However, concanavalin A had no effect on feeding or mortality of ACP in our initial experiment. However, the initial screens for both of these compounds were conducted over a brief time period (48H) and will be extended in subsequent experiments, where mortality effects may be more apparent for both compounds. Efforts to refine an artificial feeding assay to better evaluate these particular compounds are underway given that the current results caused higher than expected mortality in control treatments at 48 hours and longer.
The objective of this investigation is to determine how enhanced nutrition of citrus plants may affect Asian citrus psyllid (ACP) biology, including host acceptance behaviors and population dynamics. We have have been conducting this investigation with complementary field and laboratory experiments. Regarding field experiments, we are still following the Keyplex’ program in the field. The most recent spray of nutritional supplements occurred on February 28th. The next application (post bloom application) will be performed mid-April. Since March, we have monitored the number of psyllids on each tree within our treatment plots weekly with the tap sampling method. We plan to continue this survey during the summer season with regular nymph counts and leaf nutrient analyses. We are also performing a qPCR analysis of all trees in the experiment, 6 months after the initial one, to investigate whether the infection rate has changed, depending on whether or not plots were treated with supplemental nutrients. Currently, our data indicate that infected trees are more attractive to ACP than non-infected trees. This has been already reported from our previous laboratory experiments, but we are observing this effect in the field for the first time. The effects of the supplemental nutrient regime on psyllid population densities are currently not yet statistically significant, but we have observed a trend of more psyllids found in plots treated with nutritional supplements as compared with untreated plots. However, in the laboratory we consistently observe that psyllids are more attracted to HLB-infected plants treated with a nutritional supplement as compared with non-supplemented controls. Interestingly, we have also observed that HLB-infected citrus plants were proportionally more infested with ACP adults in choice settling assays as Ct values (measured by quantitative real time PCR showing presumably higher bacterial concentration) were proportionally lower. We plan to perform a calibration curve for our qPCR method in order to determine the amount of bacterial DNA within these citrus plant treatment samples to confirm whether degree of bacterial infection impacts psyllid preference for choosing and feeding on plants. Our next objectives are to: (1) investigate the acquisition rate of the HLB-causing pathogen by psyllids from plants treated with supplemental nutrients as compared with controls, and (2) collect volatile chemicals from plants before and after the application of a nutrient spray cycle, in order to determine how this treatment affects the volatile emission pattens from plants. Our hypothesis is that changes in volatile emissions may be affecting behavior of ACP.
This is a cooperative research project between Co-PIs Joseph Morse, Jim Bethke, Frank Byrne, Beth Grafton-Cardwell, and Kris Godfrey. One objective is to coordinate with researchers working on chemical control of ACP in Florida, Texas, Arizona, and elsewhere. Towards that end, Grafton-Cardwell, Godfrey, and Morse met with Jawwad Quershi, Phil Stansly, and 2 CA PCAs in Orlando 2-5-13 at the Third International HLB conference to discuss cooperative trials focusing on organic products; the same group toured the UF Immokalee Research Center 2-6-13 to see ongoing field trials; and Byrne and Morse traveled to the UF Lake Alfred Research Center with 3 CA PCAs 2-8-13 to discuss ongoing research and collaboration with Michael Rogers and Lukasz Stelinski. The Orlando HLB conference is an excellent opportunity to network with other scientists working on ACP and HLB and much was learned and discussed. We are rearing ACP in a contained greenhouse at the Chula Vista Insectary (San Diego County; about 6 miles north of the Mexican border) under permit (#2847) from CDFA. This permit clearly notes experimental protocols and procedures so that the work is done as safely as possible to minimize the chance of ACP escape. At this site, Jim Bethke has initiated ACP tests on various organic and traditional pesticides of interest to California growers using 4 types of tests: adult topical adult drench adult residual and nymph topical tests. Data have been gathered to date on 14 traditional pesticides and 12 organic products, in many cases with multiple trials involving each material. A second location where we are working with ACP is at UC Riverside, working under permit inside the UCR Insectary Facility. Frank Byrne is conducting trials on various neonicotinoid insecticides and Morse is evaluating the baseline susceptibility of CA ACP to various pesticides (18 trials to date) in comparison with studies done in Florida. Two field trials have been run to date evaluating organic products useful in control of ACP; the first 10-4-12 evaluated the impact of 5 treatments on adult ACP; the second trial 3-5-13 evaluated 8 treatments against young nymphs and eggs. Kris Godfrey obtained a permit to rear ACP inside UC Davis’ Contained Research Facility and received 4 shipments of ACP (under CDFA permit) from Bethke’s colony to start the Davis colony (so that Chula Vista and Davis results might be similar). She has initiated testing of organic products and has several other lines of experimentation planned based on requests from the CRB. Beth Grafton-Cardwell has updated online ACP pest management guidelines and has given 8 presentations to various groups dealing with ACP since 10-1-12 (i.e. over the past 6 months). She has served as a focal point for communicating with ongoing ACP management programs in the SJV, Ventura, and elsewhere. In summary, we continue to expand our ability to conduct ACP research in California with a clear focus on management of HLB (rather than ACP).
Our project goal is to develop a system for inoculating Asian citrus psyllid (ACP) with a native pathogenic fungus, Isaria fumosorosea (Ifr), and use these infected psyllids as ‘autodisseminators’ to effectively spread the pathogen among ACP populations in residential citrus. Research goals for 2012-2013: (1) Conduct field trials to determine if Ifr-inoculated ACP adults can infect nymphs in residential citrus, (2) Determine seasonal and environmental effects on infection levels, (3) Evaluate pathogen dispersal, (4) Assess pathogen effects on arthropod biological control agents. Main Findings: “Infection of ACP in dooryard citrus”. A field trial was conducted during April to May of 2012 with Mexican lime trees at the ‘Victoria Palms’ RV park in Donna, TX. Ten adult ACP were dusted with Ifr inoculum and released into mesh bags placed around shoots with nymph clusters. Each test tree contained one to four clusters; a total of 15 clusters on 10 trees were tested. A separate set of nymph clusters (n = 15) measured ambient levels of Ifr infection. In the control clusters, we found few dead individuals and no Ifr-infected psyllids. In clusters exposed to dusted adults, a mean of 39% of the psyllids were infected. For a follow-up trial at ‘Victoria Palms’ during July to August of 2012, 100 ACP adults were dusted and released on the north-west and south-east canopies of Mexican lime trees (n = 4) and grapefruit trees (n = 8). Identical numbers of ‘control’ trees were used to measure ambient levels of Ifr infection. After 3 weeks, we inspected two nymph clusters from both sides of each tree and found no Ifr-infected individuals on control trees, no significant effect of canopy aspect on infection levels, a mean of 16% infected individuals on lime trees and 6% on grapefruit trees. These trials demonstrated that dusted psyllids could infect nymphs in open clusters on residential trees under summer weather conditions in Texas. “Susceptibility of immature Tamarixia radiata to Ifr spores”. During November 2012 to February 2013, we evaluated susceptibility of Tamarixia radiata, a parasitoid wasp used for biological control of ACP, to Ifr spores before and after ACP mummification. To evaluate susceptibility of T. radiata prior to ACP mummification, we exposed ACP nymphs to adult female wasps for 24 h and waited 96 h before confirming parasitism of individual nymphs. Each parasitized nymph was transferred to a citrus leaf disk and then dusted with Ifr inoculum (n = 20). A separate set of parasitized nymphs was transferred to leaf disks but not exposed to Ifr (n = 20). Wasp eclosion was 14 times greater among control nymphs than Ifr-dusted nymphs. To evaluate susceptibility of T. radiata after ACP mummification, we transferred parasitized ACP nymphs to leaf disks but waited until mummification (approximately 168 h after parasitism) before dusting half of the mummies with Ifr inoculum (n = 17) and leaving the other mummies as controls (n = 17). Wasp eclosion was 48% among mummies dusted with Ifr and 65% among controls. These trials demonstrated that susceptibility of immature T. radiata to Ifr spores is greatly reduced after ACP mummification. “Susceptibility of immature Tamarixia radiata to Ifr hyphae”. During March 2013, we evaluated the susceptibility of T. radiata to Ifr hyphae after ACP mummification. We allowed parasitized ACP nymphs to mummify on leaf disks before exposing half of the mummies to Ifr hyphae (n = 23) and leaving the other mummies as controls (n = 23). Wasp eclosion was 17% among mummies exposed to Ifr hyphae and 78% among controls. These trials demonstrated that immature T. radiata are susceptible to Ifr hyphae after ACP mummification.
This project began 11/1/2012 and our efforts are now ongoing. We have colonies of both psyllids (Bactericerca cockerelli and Diaphorina citri) to be used in our work and are using both for our studies here. We have created a series of transgenic plants to compare general tissue (35S promoter) and specific phloem (AtSus2) expression of anti-psyllid (B. cockerelli initially) sequences for their potential to induce RNAi effects on psyllids. We have also begun constructing artificial mirco RNA interfering RNAs as a strategy to deliver specific anti-psyllid RNAs to psyllid targets. Three 21-nt-sequences of the Bactericerca cockerelli ATPase (BC-ATPase) gene were used to construct artificial microRNAs (amiRNAs). MIR319a has been used as a backbone of amiRNAs and therefore is chosen for our amiRNA constructions. The sense and complementary strands of three 21-nt-sequences were generated. One of the three 21-nt-sequences was also created using primer extension to have a amiRNA with shorter stem-loop. Therefore, the total of 7 amiRNAs targeting BC-ATPase were made and cloned into pBluescript SK, which are pAMIRA1, pAMIRA1c, pAMIRA2, pAMIRA2c, pAMIRA3, pAMIRA3c, and pAMIRA2PE. These constructs, plus appropriate controls will be used 1, for in vitro transcription and the RNA transcripts will be used for psyllid-feeding experiments; 2, to construct into a which can generate the amiRNAs in plants, and 3, to clone into a binary vector for transient expression by agro-infiltration. We will begin evaluations for effects very soon and will utilize positive results to move towards targeting D. citri. We are also attempting to identify the actual forms of RNAi-inducing RNAs that are present in plants. To determine if the double-stranded RNA induced siRNAs can move systemically in plants through the phloem for psyllids to acquire, the full-length BC-ATPase sequence was inserted into an agroinfection-compatible TMV expression vector. The BC-ATPase TMV will be infiltrated into Nicotiana benthamiana plants and the newly emergent leaves will be used to detect for siRNAs of BC-ATPase by Northern blot analysis. We will also perform bioassays on these leaves to determine whether or not RNAi effects can be induced in recipient psyllids.
We have made further progress on nucleotide sequence and bioinformatics analyses of Diaphorina citri samples from several worldwide locations in order to identify candidate D. citri-infecting viruses. We are continuing to sequence and characterize the D. citri reovirus that we have already identified from Taiwan samples. We have re-constructed a new small RNA library for the Taiwan D. citri RNA samples and we hope that we can generate additional contigs this time in order to identify the full genome sequence of the reovirus, but also we hope that deeper sequence analysis may identify additional viruses as the RNA quality of these samples was excellent. This virus is confirmed also to be in psyllids from China, but not from Brazil. It is likely present in Florida D. citri samples due to previous reports, but we have failed to confirm these at this time. We have also now generated small RNA libraries for Diaphorina citri RNA samples from China and Brazil. Both of these RNAs showed good quality with RIN (RNA integrity number) ‘ 8. After validating cDNA constructs, we submitted these two libraries to BGI (Beijing Genome Institute) sequence facility in Hong Kong for deep sequencing in Illumina`s Solexa platform with HiSeq system. We are waiting for these sequences to start data analysis. We also have received five new RNA samples from Florida and samples from Pakistan. After analyzing RNA quality, three of the Florida samples were selected for small RNA library construction and deep sequencing. Right now, we are generating these libraries and they will be sent for sequencing soon. We have now established a virus-free D. citri colony within the UC Davis Contained Research Facility. We will use these psyllids for biological assays as D. citri viruses are discovered and prove to be workable.
The overall goal of this 3-year research project is to efficiently deliver antimicrobial molecules into citrus phloem against the HLB bacterium. This quarterly (from Jan 2013 to April 2013) research continued to optimize the W/O (water in oil) and O/W (oil in water) nanoemulsion formulations by evaluating the ideal adjuvant mixtures of solvents, oils, lipophilic and hydrophilic surfactants using pseudo-ternary phase diagrams and thermodynamic stability methods. Several W/O and O/W nanoemulsion formulations were screened for further preparation of optimum W/O or O/W solutions using pseudo-ternary phase diagrams with oil as the oil phase, water as the aqueous phase, and combinations of lipophilic surfactant, hydrophilic surfactant and water-miscible solvent as mixed phase. We have developed a method for screening penetrants on citrus and used this to evaluate and quantitate several penetrants on different cuticle types. This will used to select the best penetrants for further application. First round tests on LIberibacter control have been conducted on seven compounds from the Citrus Research and Education Center, IFAS, UF and one compound, epsilon-L-polyline, from China. The second round tests will be done in the next quarter. The future work will be focused on the following: 1) evaluating penetration ability of chemical compound and penetrants through the citrus cuticle; 2) Evaluating drug loading capacity using the optimized nanoemulsion formulations; 3) Optimizing the final formulations by combination of screened penetrants and high drug loading capacity formulations.
Progress on development of an acoustic trap to capture male Asian citrus psyllids (ACP) that are searching for females on citrus tree branches continued in the first quarter of 2013. By the end of the previous quarter, we had programmed an Arduino Uno microcomputer system to detect and record psyllid-produced vibrations from a microphone attached to a citrus tree branch. We now have programmed the system to play back ACP communicatory signals whenever it detects a male calling on the branch. The signal playback is done through an inexpensive piezoelectric buzzer system. In the last two weeks, we have begun the process of incorporating the microphone-buzzer microcomputer-controlled system into a trap for testing in field environments. Earlier in the quarter, we also presented some of the initial findings at the 3rd International Research Conference on Huanglongbing in Orlando, FL. One paper on this research is in press, and two others are in progress.
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 developed 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. Objective 2. Stelinski’s lab initiated an experiment to study the effect of adult density (crowding) on ACP dispersal behavior. For two days, psyllids are allowed to settle on Valencia plant citrus plants in the laboratory. Densities of psyllid released varied from 1 ACP per cm of leaf flush to 10 ACP per cm (1:1 sex ratio). After two days, four new Valencia plants were introduced into each cage. Each day, over the course of one week, psyllids that dispersed from the original plant to the newly introduced plants were removed and sexed. An increase in the number of dispersing ACP was observed with increased psyllid density. Females were also observed to be more sensitive to ACP density than males, and consequently dispersed sooner than males at lower crowding levels. Currently, they are conducting experiments that vary the sex ratio of the ACP released in the crowding experiments. Based on previous results showing that females repel one another at high densities of crowding, it is hypothesize that for a given psyllid density, increasing the proportion a females should increase female tendency to disperse. Experiments were also initiated to investigate how infection of psyllids with Candidatus Liberibacter asiaticus (Las) affects dispersal behavior. Using a flight mill technique, it was seen that a small portion of psyllids initiate long flights, while most appear to only fly for short periods. Why do some psyllids initiate these potentially long-range flights, while others do not? Sex, mating status, level of satiation, presence of endosymbionts, and infection with the Las pathogen are all being investigated. Understanding why a small portion of psyllids undertake long range flight may provide a means of targeting long-range movers. Objective 3. Release of up to 2,000 adult ACP marked with fluorescent dye has resulted in too little recovery to draw significant conclusions so plans underway for another mark recapture trial using more adults. Objective 4. Yellow sticky traps set at three canopy heights are giving mixed results with more ACP captures in the upper canopy at in the older Charleston grove and a more even distribution at the younger and more uniform Bob Paul grove. However, traps on the east side of the trees capture 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 indicate no significant directional effects. Objective 5. A paper reporting positive results using UV reflective mulch to repel ACP the first 2 years after planting was accepted for 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. In addition the mulch has shown the ability to sigificantly slow rate of HLB spread even under high pressure. Trials to test different ways of utilizing UV reflectance such as wrapping canopies with strips of metalized mulch have commenced.
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 developed 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. In recent tests, ACP have not been responding in the wind tunnel (as previously) and photoperiod is being investigated as a possible cause. Objective 2. In the previous report, we described experiments indicating that female psyllids avoid plants that were previously infested with a high density of conspecific females, and that they are also repelled by conspecific female odors. We determined if ACP damage to plants also affects psyllid movement. We used potted citrus plants that were sectioned into two halves with Teflon guillotines. Sectioning the plants into two halves allowed us to infest only one portion of the plant and simultaneously measure psyllid movement to the non-infested portion. After 24 hr of psyllid feeding on one section of the plant, other psyllids were much more attracted to the non-infested portion of damaged plants as compared with non-damaged controls. These results indicate that plant response does not contribute to psyllid-psyllid repellency, but in contrast, there is a systemic plant response to attract other psyllids upon damage. GC-MS analysis showed that this attractiveness is likely due to increased production of methyl salicylate from damaged plants. Our current hypothesis is that specific volatiles from citrus are important for selection of trees that are already infested with psyllids (indicating a favorable host), and female odor is used by other females to avoid flush that have been over-utilized. Both signals impact psyllid movement in opposite ways. Objective 3. Preparations are underway to release more marked psyllids this year after too few were recovered last spring in the first attempt. Objective 4. Captures of ACP on yellow sticky traps set at three canopy heights are giving mixed results, depending on tree height. More ACP were captured in the upper canopy in an older mature grove. However, a more even distribution of psyllids throughout the tree canopy was observed in a younger grove. However, more ACP are captured on the east side of the trees than the west side at both locations. At all locations sampled, ACP captures are greatest adjacent to a hammock or wind break. Also, traps set up to assess ACP movement between insecticide sprayed and unsprayed blocks with low and high populations of ACP, respectively, indicate no significant differences in directional movement. Seasonal fluctuations are likely and further analysis of the data is pending. Objective 5. Results indicate that the 5 ft strip of metalized mulch is effective in repelling ACP until it is shaded out by the canopy when trees exceed 5 ft in height. However, the mulch treatment reduced incidence of HLB infection by 75% for almost 2 years. A paper reporting positive results using UV reflective mulch to repel ACP for 2 years after planting was submitted to and is now under revision for the refereed journal, Pest Management Science. Also, an article was submitted to Citrus Industry for publication in the Apr 2013 issue. Trials have begun to evaluate metalized mulch placed around 1 year old resets or adjacent to mature trees. Also metalized ribbon hung in the tree canopy is being evaluated.
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