The overall goal of this 3-year research project is to efficiently deliver antimicrobial molecules into citrus phloem against HLB bacteria. This quarter’s (from Jan. to April 2014) research continued to evaluate the penetrants based on our cuticle assay and to prepare the nano-formulations coupled with penetrant for foliar spray or bark-application. Zone of Inhibition Tests (Kirby-Bauer Test), one of the fast, qualitative assays, was used to measure the ability of nano formulations of antimicrobial agents coupled with the penetrant to inhibit the growth of microorganisms (bacillus subtilis). The chemicals penetrated easily in the cuticles from HLB-affected citrus and the old-mature leaves when compared to those from young cuticles; Nano-formulation of the antimicrobial agents coupled with penetrant significantly inhibited the growth of microorganisms. The ideal nano-formulation, based on the cuticle assay, has been applied to potted plants by bark-application of O/W and foliar spray of W/O. Compared to root-soaking application, nano-formulation promoted the uptake of the antimicrobial agents and resulted in the higher concentrations of antimicrobial agents in phloem for more 15 days. No Las bacterium was detected in any of the plants treated with Ampicillin using either the foliar or bark application nano formulation 6 months from the initial treatment. The future work will be focused on: 1) Continuing to optimize the final formulations by combinations of the penetrants and high drug loading capacity formulations; 2) Evaluating drug loading capacity using the optimized nano formulations; 3) Treating the HLB-affected citrus by foliar-spray and bark-application in the field.
Optimization of CLM pheromone trap deployment was evaluated at 3 densities (1 trap per acre, 1 trap per 3 acres and 1 trap per 5 acres). The total number of CLM captures was similar at all densities tested (F = 0.26; df = 2, 52; P = 0.77). CLM flight activity followed similar patterns among the three trap densities tested (1 trap per 0.40 ha and 1 trap per 1.21 ha: R = 0.93, P < 0.0001; 1 trap per 0.40 ha and 1 trap per 2.02 ha: R = 0.85, P < 0.0001; 1 trap per 1.21 ha and 1 trap per 2.02 ha: R = 0.89, P < 0.0001). These results showed that 1 trap per 5 acres is sufficient to obtain reliable moth counts upon which to base management decisions. A manuscript was submitted to the Journal of Economic Entomology. LD50 and LD80s for some commonly used insecticides for management of citrus pests in Florida were calculated for a susceptible CLM colony. These values are being used to evaluate possible resistance to the tested insecticides in CLM field populations. Larvae and adults from the susceptible colony were exposed for 48 h to different doses (0; 0.01; 0.03; 0.1; 0.3; 1; 3; 10; 30; 50; 100, 300, 600 and 1000 ppm) of the following insecticides: Actara 25WG, Agri-Mek 0.15EC, Cyazypyr, Danitol, Delegate WG, Dimethoate, Intrepid 2F and Micromite 80WGS. The following baselines have been obtained so far for their active ingredients against larvae: Actara (thiamethoxam) LD50=2.813 (CL95: 1.07-6.46) ppm, LD80=619.176 (CL95 199.10-3100.06) (n = 681; .2 = 3.81; d.f = 7; Heterogeneity = 0.76); Agri-Mek (abamectin): LD50= 0.097 ppm (CL95: 0.05-0.16), LD80=2.61 ppm (CL95: 1.41-6.04) (n = 743; .2 = 2.03; d.f = 5; Heterogeneity = 0.41); Cyazypyr (cyantraniliprole): LD50=49.55 ppm (CL95: 18.36-129.61), LD80=27,94 (CL95: 6,19.4-0,29E+06) ppm, (n = 1,021; .2 = 2.22; d.f = 5; Heterogeneity = 0.44); Delegate (spinetoram): LD50=3.56 (CL95: 0.16-20.92), LD80= 201.83 (CL95: 31.70-53761.1) ppm (n = 859; .2 = 19.43; d.f = 5; Heterogeneity = 3.88); for Dimethoate (dimethoate) LD50=1.56 ppm (CL95: 0.15-56.31) and LD80=497.45 ppm (CL95: 22.27-0.37E+09) (n = 546; .2 = 13.07; d.f = 6; Heterogeneity = 2.18); and Micromite (diflubenzuron): LD50=88.32 (CL95: 20.69-246.69) LD80=1800.5 ppm (CL95: 522.84-75810.00), (n = 714; .2 = 10.31; d.f = 5; Heterogeneity = 2.06). A different bioassay technique is being developed for Intrepid. After testing 309 larvae with Danitol, a dose of 600 ppm only resulted in larval mortality of 52%. Due to the high a.i. rates used and low mortality values, no higher doses will be tested with this product. LD50 and LD80 for Delegate, Intrepid and Micromite are being currently being estimated for adults (n = 487, n = 703, n = 381 individuals already tested respectively). CLM larvae were collected for testing from 5 commercial citrus groves with different ACP and CLM insecticide management programs: Bob Paul, Moreno Tanner Road, Silver Strand B9, Duda and PTG. Potential resistance to Agri-Mek in these field populations was assessed by obtaining mortality rates from exposure to the previously obtained LD80 for this product, 0.097 ppm. Larval mortalities thus obtained were 0.76 (n = 33), at Bob Paul, 0.76 (n = 44) Tanner Road, 0.70 (n = 80) at B9, 0.82 (n = 44) at Duda, and 0.80 (n = 50) at PTG. Thus, mortality In all cases was similar to that observed in the laboratory susceptible colony (0.80) indicating no measurable resistance to this product yet in the field populations tested. More individuals and sites will be tested for Agri-Mek and other insecticides this spring and summer.
This is one-year enhanced project of CRDF#584. The goal of this enhanced project is to evaluate the effective compounds, which were formulated for nano-emulsion delivery, in the field. This quarter (from Jan. 2014 to April 2014) research continued greenhouse tests and began field trials. The preliminary results from the greenhouse experiment showed that bark application of the O/W or foliar spray of the W/O were the best application methods to deliver the compound into phloem against Las bacterium, when compared to root-soaking. Nano-formulation of the effective compounds coupled with the screened penetrants increased the uptake of antimicrobial compounds. More than 30 HLB-affected citrus trees were pruned, fertilized and treated with the tested nano formulation of effective compounds in Dec. 2013. Two antimicrobial compounds were loaded into the nano formulation of W/O (Water in Oil) coupled with insecticide oil for foliar spray or O/W (Oil in Water) for bark application. Trunk injection and treatment without antimicrobials were used as controls. Each treatment was repeated for three times. Chemical treatment applications will be made every one month when flush is present starting with the spring flush in 2014. All trees involved in this experiment were confirmed to be Las-positive via a real-time quantitative polymerase chain reaction (qPCR) assay. ACP populations will be recorded by stem-tap sampling. Citrus effects of the treatments will be investigated, including: a) reduction in fruit drop; b) increased canopy density; c) reduced HLB symptoms; d) increased root uptake; e) residues and phytotoxicity. Las titers will be monitored via qPCR.
In order to speed up their application and registration for use by the citrus industry, this one-year enhancement project will immediately test these antimicrobial compounds in the field. The proposed research will focus on evaluating the efficiency of compounds against the Las bacterium in HLB-affected field citrus. In this quarter (Jan to March, 2014), we continued the field trial. The pruned trees were treated with six antimicrobial molecules that have been shown to be effective against Las in graft assays and potted plant experiments using three delivery methods. The treatments will be repeated once a month. The samples will be taken every two months and analyzed for Las and HLB disease. Phytotoxicity was observed in some of the trunk-injection treatments. In these cases, treatment was suspended. We will track this temporal phytotoxicity in next quarter. If the treated trees recovered normal growth in next quarter, we will continue the trunk-injection at lower concentration of the compounds.
Objectives: 1) scale up production of Tamarixia radiata to levels to better assess the potential impact an augmentation program may have on the ACP population and ultimately the spread of HLB, 2) genetic techniques to identify parasitoids, and 3) extend rearing technology to both private and public sectors. This year, 1.3 million T. radiata were produced between Southwest Florida Research and Education Center (SWFREC), Immokalee and Division of Plant Industry (DPI) facilities in Gainesville and Dundee, Florida. The colony of Florida strain maintained at SWFREC produced 231,300 wasps. An additional colony of the same strain and others from South China, Pakistan and North Vietnam maintained in Gainesville and Dundee produced 301,637, 305,718, 194,774 and 314,162 wasps, respectively. Wasps from these colonies were used for research, to maintain colonies, for release in conventional and organic citrus and to provide the Commonwealth of Dominica with a starter colony. The Dundee facility is now up to 100,000 wasps per month, with production is expected reach 3 million per year, thus enabling more releases and greater impact on psyllid populations. Releases were made in Collier, Lee and Hendry, Lake, Indian River, St. Lucie, Polk, Hardee, Alachua, and Hillsborough counties. Laboratory experiments showed that T. radiata fecundity increased to a maximum 12 eggs per day per female with increasing host density up at 40 nymphs per female wasp per day with no significant increases at higher densities. ACP populations have generally been low in iSW Florida so parasitism rates were evaluated on both feral populations and infested sentinel plants placed in the field. About 12,000 parasitoids were released between April and June in a 13-acre block of ‘Valenica’ in Collier Co. used to evaluate 4 treatments: insecticides, nutritionals, insecticides + nutritionals and untreated. Parasitism of feral nymphs reared from untreated plots averaged 17% in April with no more parasitism except for 3% in nutrition + insecticide treatment. Sentinel plants containing an average 54 nymphs each were hung in trees during June. Parasitism averaged 4% (0-33%) and 7%, (0-69%) in nutritional and untreated plots with releases, compared to 7% (0-31%) and 2% (0-8%), respectively, in plots without releases. Parasitism on sentinel plants averaged 20-22% in the untreated and nutritional treatments after 7,500 parasitoids were released in July. Only 3% feral nymphs collected from untreated and nutritional treatments were parasitized and none in the insecticidal treatments. Psyllid adults averaged below 0.2 per tap sample so insecticides were not used for 3 months prior to the evaluation. At SWFREC, 27,000 Tamarixia were released between April-June and parasitism averaged 0-18% in June in the blocks treated with insecticides. In July and August, 3,000 and 2,450 Tamarixia were released, respectively. In July, parasitism averaged 28% in the release block compared to 0.5 % in no release blocks. In August, parasitism increased to 38% in the release block compared to 17 % in no release blocks. Similar trends of parasitism were observed in fall mainly from young blocks producing new growth required for nymphal survival. In Hendry county, 8,800 Tamarixia were released Oct-Nov. Parasitism in the release and no release plots averaged 63% and 35%, respectively, in Oct and 38% and 54%, respectively, in Nov, indicating spread to no release areas. A large scale study evlauting biweekly mass release and respective control without release or insecticide interventions in three organic groves was initiated March 2014.
The main objective of this research is to determine both abiotic and biotic factors that regulate Asian citrus psyllid (ACP) acceptance of plants and pathogen transmission. The goal is to use this information to interfere with the vector’s capability of transmitting pathogen between citrus trees. We have identified a portion of the designated sequence of the CsSAMT gene involved in methyl-salicylate production in citrus. Following this discovery, we conducted an investigation to determine whether abundance of CsSAMT mRNA is correlated with expression of methyl-salicylate, as well as, ACP feeding. We exposed plants to feeding damage by 100 caged psyllids and compared the volatile profile of these plants 24h after psyllid infestation with uninfested control plants. We found that the amount of methyl-salicylate synthetized per leaf increased, as well as, the abundance of CsSAMT mRNA, suggesting that we identified the gene involved in methyl-salicylate production in citrus. This is an important step because methyl-salicylate has been identified as the major volatile driving attraction of the Asian citrus psyllid to HLB-infected citrus. We plan to test if this gene could be activated (1) by the infection by the CLAS pathogen, and (2) by priming of the plant with volatiles from adjacent infected plants. We also plan to investigate the expression of this gene depending of abiotic factors such as drought stress and ambient temperature. Regarding the field portion of this investigation, we plan to repeat the field experiment performed last year to better understand how abiotic and biotic factors may affect psyllid population growth. In the previous year, we observed that reset trees in groves consisting of a mixture of mature and reset trees suffered less psyllid infestation and HLB infection than reset trees planted within a grove solely composed of reset trees. To confirm these results we plan to repeat this experiment this year in two groves. Additionally, we aim to better understand the mechanism(s) causing these differences. The first hypothesis is that a grove plot that is only composed of reset trees receives more light per day than a plot mostly comprised of mature trees. To test this hypothesis, we will compare the population of psyllids on citrus trees next to wind break trees versus unprotected (no wind break) citrus trees on the edges of replicated groves. A second hypothesis that we are currently investigating is that volatile release by resets trees is modified depending on the environment surrounding trees. Specifically, we are focusing on whether the neighboring tree communicates with its neighbors via volatile release depending on infection status. The hypothesis is that infected plants may ‘prime’ uninfected plants to release volatiles that assist in plant protection. Our plan is to collect leaf volatiles in citrus plots that either consist of a contiguous replanting of immature citrus or within plots that contain a mixture of mature citrus and replants.
The objective of this research is to evaluate non-neurotoxic insecticides against Asian citrus psyllid (ACP), and suggest additional tools to growers for management of ACP. We are investigating those non-neurotoxic insecticides that have shown promise against insect pests similar to ACP. These additional tools may not only prove effective against ACP, but also could assist in ACP resistance management programs as needed tools for effective rotation with current insecticides. In this quarter, we have concentrated on small-plot field trials to evaluate two possible non-neurotoxic chemicals identified from laboratory studies for their effectiveness in reducing Asian citrus psyllid (ACP) populations. We compared tebufenozide (Confirm 2F), methoxyfenozide (Intrepid 2F ) with the commonly used neurotoxic insecticide imidacloprid (Provado 1.6 F) under field conditions. Plots consisting of four trees of ‘Hamlin’ sweet oranges were sprayed on April 29, 2014 with Intrepid 2F at 16 oz per acre, Confirm 2F at 16 oz per acre, Provado 1.6F at 20 oz per acre or an untreated control plot. The plots were replicated four times. At 3, 7, 14, 21, 28 and 35 days post-treatment, the adult ACP population was estimated by taking 10 tap counts on the four trees in each plot. At the same time, 10 flush were removed from the trees and the nymphal population ranked with 0=no nymphs, 1=1-5 nymphs, 2=6-10 nymphs and 3=< 10 nymphs. There were no significant differences in the population of adult ACP after treatment with Confirm 2F and Intrepid 2F as compared with the untreated control, whereas provado significantly reduced the adult population as compared with the control. Intrepid 2 F resulted in the highest reduction of nymphs followed by Provado, and then confirm as compared with the control. Therefore, these insect growth regulators do appear to have field activity against ACP immature stages. Additionally, we are in the process of evaluating novaluron in the field at rates of 10 oz per acre and 20 oz per acre.
Since the last report, we have completed three trials to evaluate different formulations of imidacloprid. This research objective is in response to grower questions about the consistency of different imidacloprid formulations at a time when there are multiple generic products available. The trials were conducted in commercial citrus groves – one trial on minneola tangelos in the Coachella Valley, and two trials on grapefruits at separate locations in Riverside County. We have completed 3 years of trials where we evaluated the uptake of clothianidin (formulated as Belay and applied with a 1% NIS) applied by soil drench and trunk spray. The results of the 2011 trials were very promising, whereas the results of the 2012 trials showed no residues in the trees. We have now completed a third trial at Lindcove Research and Extension Center. Both the soil drench and trunk spray applications at a single timing were compared and found to be ineffective as means of administering the insecticide into the trees. In 2014, we hope to address issues with imidacloprid uptake in lemons in Ventura County. We have previously shown that the uptake of imidacloprid is inefficient on the heavy clay soils in this area. Irrigation seems to be a contributing factor in the poor uptake due to the long periods between each irrigation event. We will work with growers to investigate how shortening the frequency between irrigation events, particularly in the weeks immediately after the applications, might improve the uptake. In addition to investigations with imidacloprid, we also plan to evaluate the uptake of thiamethoxam. Thiamethoxam is a neonicotinoid insecticide that has greater water solubility than imidacloprid. With shortened frequencies between irrigations, it may be possible to get better uptake with this insecticide.
We have completed our first objective to evaluate the effects of nursery practices (watering, citrus variety, potting media) on imidacloprid uptake and retention. The trial was conducted at UCR Agricultural Operations . Two citrus varieties were selected for this trial – Parent Washington navel and Limoneira 8A lemon, both on Carrizo rootstock. The trees were budded in June 2012 and grown in 5′ pots at LREC. Trees were transferred to UCR Agricultural Operations on June 13 2013 and transplanted on June 17 to no. 5 pots. Two potting media were chosen for the study that differed principally in the proportions of sand (10-30%) and redwood (40-60%). The evapotranspiration rate was determined for the two soil mixes and this data was used to select three watering levels for the study. The three levels were defined as ‘replacement watering’ (100-120% ET), ‘overwatering (150-200% ET) and ‘severe overwatering’ (300-400% ET). For the trial, trees were placed in a 12 x 25 grid pattern and randomized according to variety, soil mix and watering level. When the trees had adapted to their new potting media environment, they were treated on July 11, 2013 with 0.33 mls Admire Pro per cu ft potting media. Monitoring for ACP on all trees was also conducted at monthly intervals for the duration of the trial, and imidacloprid residues were determined for all trees by ELISA for 28 weeks post-treatment. There were very clear differences among citrus varieties and watering levels, but somewhat equivocal effects of soil type. Imidacloprid residues were not detectable at 16 weeks after application (especially in lemon at the high watering levels). We are currently preparing to conduct the second objective which will investigate the uptake and persistence of additional neonicotinoid insecticides. The trees (Parent Washington navel on Carrizo rootstock) have already been budded at Lindcove Research and Extension Center.
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. We have begun the second year of the field experiments for this investigation. We are repeating the same protocol as last year; however, with this supplemental funding we are able to expand the investigation. This additional experiment is being conducted in a mature Valencia grove and is similar to the one we have been conducting for over a year in a Hamlin reset grove. Nutritional applications will continue to follow the Keplex’ recommendations for this year. At the end of April, we will start monitoring ACP nymph and adult populations, as well as flush development. We have also planned to screen for HLB infection status of the trees in this experiment with qPCR as we have done in the other experiment in Hamlin resets to determine how nutritional treatments may impact tree infection status. This will allow us to compare solid planting resets with mature groves.
We have initiated development of a novel insect behavior-modifying product to control the Asian citrus psyllid (ACP). Decoy is a biodegradable emulsion capable of releasing methyl salicylate (MeSA) at rates sufficient to disrupt ACP behavior and transmission of HLB, while attracting ACP insect predators and parasites to treated plots for three months. The formulation is under development by ISCA Technologies. The repellency of Decoy prototype formulations will be determined in laboratory-based cage studies. We have conducted research on how this pathosystem may affect biological control agents and how this may also be manipulated for control of ACP populations. EXPERIMENT 1: WASP RESPONSE TO VOLATILES FROM INFECTED VERSUS UNINFECTED PLANTS Las-infected plants were more attractive to T. radiata than uninfected counterparts (.2=9.76, d.f.=1, P=0.002). Similarly, uninfected plants that received damage by feeding ACP adults were more attractive to T. radiata than uninfested controls (.2=25.00, d.f.=1, P<0.001). The odors of adult ACP, in the absence of plants and/or plant damage, did not attract T. radiata as compared with blank odor controls (.2=0.03, d.f.=1, P=0.857). Finally, Las-infected plants infested with ACP were not more attractive than uninfected plants also infested with ACP adults (.2=0.12, d.f.=1, P=0.732). EXPERIMENT 2: WASP RESPONSE TO SYNTHETIC ODOR SOURCES MeSA was attractive to T. radiata at the 0.01.g dosage (.2=11.76, d.f.=1, P<0.001), but not at the 0.1.g (.2=0.93, d.f.=1, P=0.336) or 0.001.g (.2=2.79, d.f.=1, P=0.094) dosages as compared with the responses to solvent negative controls (Figure 2). Also, T. radiata were not attracted by either .-ocimene or D-limonene treatments, at dosages known to be attractive to ACP (.2=0.04, d.f.=1, P=0.835; .2=0.03, d.f.=1, P=0.853; respectively), as compared with the solvent negative controls (Figure 2). EXPERIMENT 3: EFFECT OF LAS INFECTION AND MESA LURE ON PARASITIZATION OF D. CITRI BY T. RADIATA The number of nymphs that were not found during the experiment on Las-infected versus uninfected (control) trees was not different (2.50'0.29 and 2.75'0.48, respectively). Similarly, the number of nymphs that were not found between MeSA-treated versus control trees was not different (3.00'0.40 and 3.25'0.25, respectively). Significantly more ACP nymphs were parasitized on Las-infected plants than on paired uninfected control plants in direct choice assays (Estimate= -2.37, SE= 0.43, z= -5.48, P<0.001, Figure 3a). In addition, treatment of uninfected citrus plants with a synthetic MeSA lure significantly increased parasitization of ACP nymphs by T. radiata as compared with otherwise identical uninfected plants that were not treated in this manner (Estimate= -2.50, SE= 0.42, z= -5.91, P<0.001, Figure 3b). We found that the specialist parasitoid of D. citri, Tamarixia radiata, was attracted more toward Las-infected than uninfected plants. We demonstrated that this attractiveness was due to the release of methyl salicylate. Parasitization of D. citri nymphs on Las-infected plants was higher than on uninfected controls. Also, parasitization was higher on uninfected plants baited with methyl salicylate than on non-baited controls.
We have completed the molecular cloning and characterization of the voltage-gated sodium ion channel in Asian citrus psyllid (ACP), and have designed an assay to investigate the gene frequency of allelic variations associated with pyrethroid resistance noted in other insect species as described in the January 2014 report. Validation of the assay is underway and is poised to begin screening insects from different locations across Florida concurrent with the annual field survey to monitor insecticide resistance. To better understand potential for pyrethroid resistance in ACP, we are pressuring colony insects with fenpropathrin and now several generations into a pressurized colony. In addition, we found that psyllids raised on Indian curry leaf vs. orange jasmine show a significant difference in response to fenpropathrin at the LD50 level, and are using this model to investigate the underlying biochemistry and/or molecular biology that contributes to this differential response. These results will allow us to better understand how insecticide resistance develops to pyrethroid insecticides in ACP, so we may better understand how to prevent it. This is important because pyrethroids are one of the most important insecticide modes of action currently being used for ACP management.
The objective of this study is to evaluate non-neurotoxic insecticides against Asian citrus psyllid (ACP), and provide growers with insecticides with varying mode of action for management of ACP. We are investigating those non-neurotoxic insecticides those have shown promise against insect pests similar to ACP. These insecticides with varying modes of action that differ from neurotoxic insecticides may not only prove effective against ACP, but also may assist in ACP resistance management. Diofenolan was evaluated for its ability to inhibit the egg hatch of 49-96 hrs aged eggs. Percent egg hatch inhibition of 7, 18, 31, 42, 65 and 91 % was observed when eggs were treated with concentrations of 0, 20, 40, 80, 160 and 360 ‘g/ml, respectively. To determine the effects of diofenolan on survival of various developmental stages of ACP, we treated first instar nymphs with concentrations ranging between 0-360 ‘g/ml of diofenolan. We observed 95, 69, 38, 27, 23, 8 percent survival of ACP into the second instar for 0, 20, 40, 80, 160, 320 ‘g/ml concentrations, respectively. Currently, we are investigating the effect of diofenolan on the development of third and fifth instars nymphs. We will also investigate the effect of diofenolan on fertility and fecundity of ACP females. Following completion of evaluations of diofenolan (JH analog), we will initiate evaluation of tebufenozide and methoxyfenozide (ecdysteriod agonists). The results of our research suggest that non-neurotoxic insecticides are effective in disrupting growth of the immature stages of Asian citrus psyllid and are possible useful tools as part of an integrated program.
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. Current investigations are focusing on a longer time course of effectiveness of these extracts and subsequent field testing. We have continued to analyze behaviorally active botanical oils by GC-MS to determine possible constituents that may contribute to behavioral activity in the associated laboratory and field bioassays and for development of synthetic odor blends as tools for ACP management. The components were categorized according to their relative percent area on GC-MS chromatograms have been determined. In recent evaluations, we detected nine different compounds in crushed citrus flush. The two most abundant compounds were sabinine and ocimene, followed by limonene, .-pinene, and ‘-3-carene. Low amounts of .-pinene, terpinene, phellandrene, and terpinolene were also detected. Camphor oil headspace contained a large amount of cineole and lesser amounts of limonene, .-pinene, and cymene. Sabinene, .-pinene, terpinene, phellandrene, camphene, and myrcene were also detected in camphor oil headspace. Citronella oil contained large quantities of limonene, lower amounts of citronellal, linalool, geraniol, and isopulegol. Litsea also contained large amounts of limonene and .-pinene and contained lower amounts of: sabinene, .-pinene, terpinene, cineole, camphene, myrcene, linalool, citral, and santene. Fir oil contained large amounts of .- and .- pinene, ‘-3-carene, and camphene, and lesser amounts of limonene, terpinolene, cymene, myrcene, santene, tricyclene, and bornyl-acetate. Surprisingly, clove oil did not share any major constituents with young citrus leaves (flush) utilized by ACP for egg laying and development. Clove oil was comprised of caryophyllene and eugenol, acetic acid, humulene, and furfural. GC-MS analysis was the basis for creation of two synthetic clove odor blends: a .-caryophyllene and eugenol mixture, representing the major components, and a mixture of .-caryophyllene and eugenol, acetic acid, and humulene. Settling Bioassays. In no-choice settling experiments, neither the low nor high fir oil treatment deterred ACP from settling on plants as compared with the negative control. Thereafter, ACP were presented with a choice between control plants and fir oil ‘treated plants with a single dose of fir oil released from polyethylene vials. In this case, the ACP disproportionately settled on control plants as compared with treated plants. Fir needle oil repels ACP females in laboratory assays. ACP were deterred from settling on plants treated with fir oil. Based on these results, the efficacy of fir oil as a repellent in the field may be affected by the availability of surrounding untreated citrus hosts as well as by physiological deprivation of ACP from their feeding and egg laying sources. Gravid female ACP deprived of an egg laying source for a certain period due to deployment of repellents may eventually lay eggs on plants treated with the repellent because of increased physiological need to deposit eggs as described by the rolling fulcrum model (Miller & Strickler, 1984). In other words, female ACP may eventually begin to deposit eggs on sub-optimal resources, such as those treated with a repellent, if deprived sufficiently long. In this scenario, citrus grown by homeowners among agricultural landscapes may serve as a refuge for ACP in areas where repellents, such as fir oil, are implemented for management. The proximity of backyard, or otherwise unmanaged citrus, may therefore impact the efficacy of repellents as also observed with insecticides.
The objective of this research is to evaluate non-neurotoxic insecticides against Asian citrus psyllid (ACP), and provide growers with additional tools for management of ACP. We are investigating those non-neurotoxic insecticides that have shown promise against insect pests similar to ACP. These additional tools may not only prove effective against ACP, but also could assist in ACP resistance management programs as needed tools for effective rotation with current insecticides. In the past quarter, we have been further evaluating methoprene in the laboratory. Methoprene is a juvenile hormone (JH) analog that acts as an insect growth regulator. We evaluated effects of methoprene on fertility and fecundity of Asian citrus psyllid. Reduced fertility of females was observed when they emerged from fifth instar nymphs that were treated with methoprene at 128 and 256 ‘g/ml concentrations. When female adults were topically treated with 128 and 256 ‘g/ml concentrations of methoprene, reduced fertility of ACP was observed for a week following treatment. Methoprene treatments, at 128 and 256 ‘g/ml concentrations, had no effect on the fecundity of females emerging from treated fifth instars or topically treated females. We also investigated feeding behavior of ACP adults on plant surfaces treated with methoprene concentrations ranging from 0-320 ‘g /ml. There was reduced feeding of ACP adults when placed on surfaces treated with methoprene at 160 and 320 ‘g/ml concentrations.
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