Psyllid Diaphorina Citri Kuwayama Research Articles

Inter-Population Variability of Endosymbiont Densities in the Asian Citrus Psyllid (Diaphorina citri Kuwayama).

The Asian citrus psyllid (Diaphorina citri Kuwayama) is an insect pest capable of transmitting Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening in North America. D. citri also harbors three endosymbionts, Wolbachia, Candidatus Carsonella ruddii, and Candidatus Profftella armatura, which may influence D. citri physiology and fitness. Although genomic researches on these bacteria have been conducted, much remains unclear regarding their ecology and inter-population variability in D. citri. The present work examined the densities of each endosymbiont in adult D. citri sampled from different populations using quantitative PCR. Under field conditions, the densities of all three endosymbionts positively correlated with each other, and they are associated with D. citri gender and locality. In addition, the infection density of CLas also varied across populations. Although an analysis pooling D. citri from different populations showed that CLas-infected individuals tended to have lower endosymbiont densities compared to uninfected individuals, the difference was not significant when the population was included as a factor in the analysis, suggesting that other population-specific factors may have stronger effects on endosymbiont densities. To determine whether there is a genetic basis to the density differences, endosymbiont densities between aged CLas-negative females of two D. citri populations reared under standardized laboratory conditions were compared. Results suggested that inter-population variability in Wolbachia infection density is associated with the genotypes of the endosymbiont or the host. Findings from this work could facilitate understanding of D. citri-bacterial associations that may benefit the development of approaches for managing citrus greening, such as prevention of CLas transmission.Electronic supplementary materialThe online version of this article (doi:10.1007/s00248-016-0733-9) contains supplementary material, which is available to authorized users.

First Record and Predatory Activity ofExochomus marginipennis(Leconte) (Coleoptera: Coccinellidae) onDiaphorina citriKuwayama (Hemiptera: Liviidae)

The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Liviidae) was detected in Mexico in 2002, and since then national researchers have been sampling in different production areas of citrus in order to find natural enemies with potential as biological control agents to be included in integrated pest management programs. In September 2013, an unidentified coccinellid species was observed apparently feeding on D. citri in the state of Colima, Mexico. The aim of this work is to identify this coccinellid and verify if D. citri is part of its diet. The coccinellid was identified as Exochomus marginipennis (LeConte). Under laboratory conditions feeding habits were studied, and it was verified that adults of E. marginipennis can feed on both eggs and larvae of D. citri.

Lethal and Sublethal Effects of Insecticides Used on Citrus, on the Ectoparasitoid Tamarixia radiata.

Huanglongbing (HLB) is a disease associated with the bacteria “Candidatus Liberibacter spp.” and has been devastating citrus orchards around the world. Its management involves control of the insect vector, the Asian citrus psyllid Diaphorina citri Kuwayama. However, the indiscriminate use of chemicals has caused pest outbreaks and eliminated the natural enemies of the vector, such as the parasitoid Tamarixia radiata (Waterston), the main agent for biological control of D. citri. This study assessed the lethal and sublethal effects of insecticides recommended for integrated production of citrus on the parasitoid T. radiata. When adult parasitoids were exposed to residues of 25 insecticides, 20% of them, i.e., gamma-cyhalothrin, etofenprox, azadirachtin, tebufenozide and pyriproxyfen, were considered as harmless (Class 1), 12% as slightly harmful (Class 2), 12% as moderately harmful (Class 3) and 56% as harmful (Class 4), according to the classification proposed by the IOBC/WPRS. Afterward, 14 insecticides (5 harmless and 9 harmful) were sprayed on the parasitoid pupae. Of the 14 insecticides tested, only the organophosphates dimethoate and chlorpyrifos affected the parasitoid emergence. The effects of insecticides on the parasitism capacity of adults exposed to residues of azadirachtin, etofenprox, gamma-cyhalothrin, pyriproxyfen and tebufenozide (harmless) were also evaluated. Tebufenozide and gamma-cyhalothrin affected the parasitism of the F0 generation, but did not affect the emergence of the F1 and F2 generations. Therefore, for an effective IPM program, selective insecticides or harmful pesticides to adult parasitoids could be used in the field, provided that the adults do not occur naturally and the chemical applications do not coincide with parasitoid releases.

Asian Citrus Psyllid Expression Profiles Suggest Candidatus Liberibacter Asiaticus-Mediated Alteration of Adult Nutrition and Metabolism, and of Nymphal Development and Immunity.

The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is the insect vector of the fastidious bacterium Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening disease, or Huanglongbing (HLB). The widespread invasiveness of the psyllid vector and HLB in citrus trees worldwide has underscored the need for non-traditional approaches to manage the disease. One tenable solution is through the deployment of RNA interference technology to silence protein-protein interactions essential for ACP-mediated CLas invasion and transmission. To identify psyllid interactor-bacterial effector combinations associated with psyllid-CLas interactions, cDNA libraries were constructed from CLas-infected and CLas-free ACP adults and nymphs, and analyzed for differential expression. Library assemblies comprised 24,039,255 reads and yielded 45,976 consensus contigs. They were annotated (UniProt), classified using Gene Ontology, and subjected to in silico expression analyses using the Transcriptome Computational Workbench (TCW) (http://www.sohomoptera.org/ACPPoP/). Functional-biological pathway interpretations were carried out using the Kyoto Encyclopedia of Genes and Genomes databases. Differentially expressed contigs in adults and/or nymphs represented genes and/or metabolic/pathogenesis pathways involved in adhesion, biofilm formation, development-related, immunity, nutrition, stress, and virulence. Notably, contigs involved in gene silencing and transposon-related responses were documented in a psyllid for the first time. This is the first comparative transcriptomic analysis of ACP adults and nymphs infected and uninfected with CLas. The results provide key initial insights into host-parasite interactions involving CLas effectors that contribute to invasion-virulence, and to host nutritional exploitation and immune-related responses that appear to be essential for successful ACP-mediated circulative, propagative CLas transmission.

Infection of an Insect Vector with a Bacterial Plant Pathogen Increases Its Propensity for Dispersal.

The spread of vector-transmitted pathogens relies on complex interactions between host, vector and pathogen. In sessile plant pathosystems, the spread of a pathogen highly depends on the movement and mobility of the vector. However, questions remain as to whether and how pathogen-induced vector manipulations may affect the spread of a plant pathogen. Here we report for the first time that infection with a bacterial plant pathogen increases the probability of vector dispersal, and that such movement of vectors is likely manipulated by a bacterial plant pathogen. We investigated how Candidatus Liberibacter asiaticus (CLas) affects dispersal behavior, flight capacity, and the sexual attraction of its vector, the Asian citrus psyllid (Diaphorina citri Kuwayama). CLas is the putative causal agent of huanglongbing (HLB), which is a disease that threatens the viability of commercial citrus production worldwide. When D. citri developed on CLas-infected plants, short distance dispersal of male D. citri was greater compared to counterparts reared on uninfected plants. Flight by CLas-infected D. citri was initiated earlier and long flight events were more common than by uninfected psyllids, as measured by a flight mill apparatus. Additionally, CLas titers were higher among psyllids that performed long flights than psyllid that performed short flights. Finally, attractiveness of female D. citri that developed on infected plants to male conspecifics increased proportionally with increasing CLas bacterial titers measured within female psyllids. Our study indicates that the phytopathogen, CLas, may manipulate movement and mate selection behavior of their vectors, which is a possible evolved mechanism to promote their own spread. These results have global implications for both current HLB models of disease spread and control strategies.

Toxicity of an azadirachtin-based biopesticide on Diaphorina citri Kuwayama (Hemiptera: Liviidae) and its ectoparasitoid Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae)

The bioactivity of an azadirachtin-based biopesticide (Azamax™ EC) was assessed on nymphs and adults of the Asian citrus psyllid Diaphorina citri Kuwayama using different product application methods. Its compatibility with the ectoparasitoid Tamarixia radiata (Waterston) was also assessed. Exposure of D. citri nymphs to azadirachtin by direct contact + residues, to dry residues or systemically led to mortality in laboratory bioassays. For adult psyllids, the mortality was at most 67% after 120 h of exposure to dry residues, even if using 16-fold more active ingredient than for nymphs. In the field, the biopesticide exhibited high efficacy (∼90%) in controlling nymphs, similar to that achieved with the insecticide imidacloprid (Provado® 20 SC, at 40 mg a.i. L−1) used as positive control. Azadirachtin was harmless to T. radiata larvae and pupae, but caused 77.8% adult mortality after 24 h of exposure. Despite the high toxicity to adults, the biopesticide had a low duration of harmful activity (∼3 days). Given the high efficacy against D. citri nymphs, reduced effects on the immature stages of the ectoparasitoid T. radiata and low duration of harmful activity, the biopesticide is an important alternative for D. citri population management and can be used as a substitute or in rotation with current synthetic insecticides in integrated pest management programs.

Biology ofTamarixia radiata(Hymenoptera: Eulophidae), Parasitoid of the Citrus Greening Disease VectorDiaphorina citri(Hemiptera: Psylloidea): A Mini Review

Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) is an ectoparasitoid of the Asian citrus psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Psylloidea) a citrus pest and vector of huanglongbing (HLB) or citrus greening disease. First described from what is now Pakistan, the parasitoid has been introduced deliberately or inadvertently throughout Asia and the Americas wherever the psyllid now occurs. Interest in T. radiata for biological control of D. citri has grown in response to continued spread of ACP and HLB, and the evident searching and colonization capabilities of the parasitoid. Mass release is seen as a potential strategy to augment area wide management of D. citri, particularly where pesticides are not extensively used. Efficient mass rearing and eventual success of these programs will require the best possible information on biology of T. radiata including life history parameters, host relationships, sensory perception, environmental responses and genetics. Much early literature on T. radiata is in Chinese and therefore inaccessible to those not able to read the language. The present review covers the literature through 2014. The intent is to summarize what is known about biology of T. radiata to aid research efforts, with the objective of contributing to more effective biological control of this pest.

Translating Anatomical Structures and Functional Genomics of Candidatus Liberibacter asiaticus and solanacearum Into Circulative, Propagative Vector-Mediated Transmission Processes

Ca. Liberibacter asiaticus is the putative fastidious bacterial causal agent of citrus greening disease, also known as Huanglongbing (HLB), translated from Chinese as yellow dragon disease. The HLB bacterial pathogen is indigenous to Asia but has been introduced and dispersed to citrus throughout the Americas. A related bacterium that is indigenous to the Americas causes damage to potato (zebra chip) and tomato (vein-greening) and other solanaceous hosts. The causal agents are propagative and circulative in the psyllid vector, Diaphorina citri (Kuwayama) and Bactericera cockerelli (Sulc.), the Asian citrus and potato (or tomato) psyllid, respectively. The specific psyllid proteins that are indirectly or directly involved in the circulative, propagative transmission pathway are not known. However, if proteins were known that function at key points in the pathway e.g. post-ingestion, infection, biofilm formation, nutrition, circulation, and/or acquisition were known, such knowledge could be exploited to knock out their expression and abate pathogen transmission. To this end a combined approach involving functional genomics and anatomical localization of the bacterium is being implemented.  Results indicate that Ca. Liberibacter establishes biofilms on the outer surfaces of the alimentary canal and salivary glands of the Asian citrus psyllid (ACP) Diaphorina citri Kuwayama and the potato psyllid (PP) Bactericera cockerelli Sulc. In silico transcript profiling of infected and uninfected ACP and PP identified a number of mis-expressed, unique transcripts (unitrans). Functional predictions (gene ontology associations) implicate certain of these unitrans in Ca. Liberibacter infection of the psyllid host and/or in psyllid-mediated Ca. Liberibacter transmission processes.

A Comparative Transcriptomic Approach to Elucidate Psyllid-Ca. Liberibacter Interactions

Citrus greening is the most destructive disease of citrus crops worldwide. The introduced Asian citrus psyllid (ACP) Diaphorina citri Kuwayama transmits the (putative) causal bacterium, Candidatus Liberibacter asiaticus. A close relative, Ca. L. solanacearum, is the pathogen associated with Zebra chip disease of potato and vein-greening disease of tomato. It is both transmitted by and propagative in the endemic (western U.S) potato psyllid (PoP) Bactericerca cockerelli Sulc. The PoP occurs widely in the western U.S. and so has been used as a parallel study system for the quarantined ACP-greening complex. To identify proteins involved in global psyllid-Ca. Liberibacter interactions, the ACP and PoP transcriptomes were sequenced, yielding a total of 45,976 and 82,224 Illumina unique ACP and PoP transcripts, respectively. Cluster analysis revealed a high degree of sequence and transcript conservation suggestive of roles in core growth and developmental processes, providing the first molecular snapshot of the specific psyllid genes responsive to parasite invasion and circulation in the host. Evidence of inter-psyllid molecular conservation substantiates the suitability of PoP as a study system for ACP-Ca. L. asiatcus. Comparative in silico expression analysis within and between psyllid species revealed predicted functions involved in Ca. Liberibacter parasitism that were both unique and shared in common among adult and nymphal instars. In addition, functional characterization based on Gene Ontology analysis has revealed a number of genes associated with host-parasite interactions that could mediate Ca. Liberibacter infection, propagation, and circulation in the psyllid, as well as transmission processes.

RNA Interference Screening Reveals Redox Processes to be Most Responsive to Low dsRNA Doses in Asian Citrus Psyllid

The Asian citrus psyllid (Diaphorina citri Kuwayama) is an invasive Homopteran that has crippled citrus production in Florida with the spread of the Huanglongbing (Citrus Greening) disease, which yields small discolored and bitter fruit. The disease is associated with the bacterium ‘Candidatus’ Liberibacter and is rapidly spreading to other citrus producing states. Gene targets were competitively deposited by experts from diverse fields for RNAi screening through an Innocentive challenge funded by the Citrus Research and Development Foundation. Four of the fifty genes were identified in dsRNA feeding trials to induce both significantly high mortality as well as concentration dependent dose response. Three of these are involved in redox biochemistry. These results indicate that gene silencing of proteins involved in metabolism by redox chemistry can induce mortality at low doses and that functional targeting in this organism may be the best strategy for psyllid control by RNAi.

Targeting juvenile hormone metabolic genes in the Asian citrus psyllid (Diaphorina citri Kuwayama) as a strategy to reduce the spread of citrus greening disease

Author(s): Van Ekert, Evelien; Borovsky, D.; Powell, C. A.; Cave, R. D.; Alessandro, R. T.; Shatters, Jr., R. G. | Abstract: Diaphorina citri Kuwayama, the Asian citrus psyllid (ACP), is a devastating citrus pest due to its transmission of a phloem-limited bacterial pathogen, Candidatus Liberibacter asiaticus, that causes citrus greening. Psyllid control is a major part of effective greening disease management, and our research targets perturbation of insect juvenile hormone metabolism as a new psyllid control strategy.n Previous studies have shown that application of a juvenile hormone (JH) analogue, pyriproxyfen, is known to produce ovicidal/nymphicidal effects, morphological abnormalities, and reduced fecundity in ACP adults. These observations prompted us to identify JH biosynthetic and degradative pathways as targets for biologically-based control strategies, including RNA interference, as alternatives to heavy reliance on broad-spectrum pesticides. First, candidate genes/cDNAs encoding the JH metabolic enzymes, juvenile hormone acid methyl transferase (JHAMT) and juvenile hormone esterase, were identified through computational analysis of the D. citri genome. Second, JHAMT cDNA was cloned, expressed in E. coli and a functional protein was purified. This JHAMT had a high affinity for substrates leading to JHI and JHIII synthesis, making it plausible that both juvenoids are present in the ACP. Results are discussed with respect to mechanism(s) of juvenile hormone biosynthesis/catabolism in the ACP and targeting this process as an interdiction point for a bio-rational ACP control strategy.

Recommended pesticides persistence for integrated citrus production on ectoparasitoid Tamarixia radiata (Waterston, 1922) (Hymenoptera: Eulophidae)

Tamarixia radiata (Waterston, 1922) is the main biological control agent of the psyllid Diaphorina citri Kuwayama, vector of bacteria associated with Huanglongbing in citrus. However, indiscriminate use of chemicals affects its control rate. Thus, this study assessed the biological persistence of 22 insecticides, two oils and 16 acaricides recommended for the control of citrus pests, on the parasitoid T. radiata. For this, the parasitoid adults were exposed to waste products sprayed on citrus seedlings of the variety Valencia. After 3, 7, 10, 17, 24 and 31 days after spraying, leaves were removed and in the laboratory, leaf discs of 4.0 cm diameter were obtained with the aid of a metallic punch , and were placed in Petri dishes (4.5 cm diameter) on a gelled mixture of water-agar to 2.5%. Thereafter, 10 parasitoid adults of 48 hours of age were placed on each plate and, then, placed in a climate clamber (25 ± 1 ºC, 70 ± 10%, 14L10D). Each treatment had five replicates. Insect mortality was evaluated 24 hours after exposure to residues. Insecticides Saurus, Turbo, Mimic 200 SC and Azamax; mineral oil Argenfrut; vegetable oil Nortox and acaricides Vertimec 18 EC, Envidor, Sanmite, Torque 500 SC, Cascade 100, Borneo, Dicofol, Micromite 240 SC and Savey WP were classified as short lived, and insecticides Tracer and Dicarzol and acaricide Marshall Star were classified as persistent. Therefore, it is essential to use selective products in integrated pest management to preserve the parasitoid.

Botanicals, selective insecticides, and predators to control Diaphorina citri (Hemiptera: Liviidae) in citrus orchards.

The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama vectors pathogens that cause huanglongbing (HLB) or citrus greening devastating and economically important disease present in most citrus growing regions. Young citrus shoots are required for psyllid reproduction and development. During winter citrus trees produce little or no new growth. Overwintering adults reproduce in spring on newly emerging shoots also attractive to other pests and beneficial insects. Botanicals and relatively selective insecticides could help to conserve beneficial insects and reduce pest resistance to insecticides. Sprays of Azadirachtin (Neem), Tropane (Datura), Spirotetramat, Spinetoram, and broad-spectrum Imidacloprid were evaluated to control ACP in spring and summer on 10-year-old "Kinow" Citrus reticulata Blanco trees producing new growth. Psyllid populations were high averaging 5-9 nymphs or adults per sample before treatment application. Nymphs or adults were significantly reduced to 0.5-1.5 per sample in all treatments for 3 weeks, average 61%-83% reduction. No significant reduction in ladybeetles Adalia bipunctata, Aneglei scardoni, Cheilomenes sexmaculata, and Coccinella septempunctata was observed. Syrphids, spiders and green lacewings were reduced in treated trees except with Tropane. Studies are warranted to assess impact of these predators on ACP and interaction with insecticides. Observed reduction in ACP populations may not be enough considering its reproductive potential and role in the spread of HLB. Follow-up sprays may be required to achieve additional suppression using rotations of different insecticides.

Comparison of Potato and Asian Citrus Psyllid Adult and Nymph Transcriptomes Identified Vector Transcripts with Potential Involvement in Circulative, Propagative Liberibacter Transmission

The potato psyllid (PoP) Bactericera cockerelli (Sulc) and Asian citrus psyllid (ACP) Diaphorina citri Kuwayama are the insect vectors of the fastidious plant pathogen, Candidatus Liberibacter solanacearum (CLso) and Ca. L. asiaticus (CLas), respectively. CLso causes Zebra chip disease of potato and vein-greening in solanaceous species, whereas, CLas causes citrus greening disease. The reliance on insecticides for vector management to reduce pathogen transmission has increased interest in alternative approaches, including RNA interference to abate expression of genes essential for psyllid-mediated Ca. Liberibacter transmission. To identify genes with significantly altered expression at different life stages and conditions of CLso/CLas infection, cDNA libraries were constructed for CLso-infected and -uninfected PoP adults and nymphal instars. Illumina sequencing produced 199,081,451 reads that were assembled into 82,224 unique transcripts. PoP and the analogous transcripts from ACP adult and nymphs reported elsewhere were annotated, organized into functional gene groups using the Gene Ontology classification system, and analyzed for differential in silico expression. Expression profiles revealed vector life stage differences and differential gene expression associated with Liberibacter infection of the psyllid host, including invasion, immune system modulation, nutrition, and development.

Abdominal Color of the Asian Citrus Psyllid (Hemiptera: Liviidae) is Associated with Flight Capabilities

Abstract We examined the propensity for flight initiation and flight capability of the Asian citrus psyllid (Diaphorina citri Kuwayama, Hemiptera: Liviidae) with a flight mill. We measured continuous flight by D. citri for up to 3 h, which equated to a distance of ≈2.4 km. We compared the flight capability of D. citri depending on their sex and morphotype (color of abdomen). Two general morphotypes exist within this species: green-blue and gray-brown. We observed that ≈32% of psyllids from the green-blue morphotype tested exhibited long durations of flight (>60 s); whereas <5% of psyllids from the gray-brown morphotype performed such long duration flights. There was no significant difference in flight performance between the two sexes within both the gray—brown and green—blue morphotypes. Furthermore, psyllids from the gray—brown morphotype were characterized by smaller pronotums and shorter wings than psyllids from the green—blue morphotype. In addition, males, in general, were characterized by smaller pronotums and shorter wings than females. However, neither pronotum nor wing size were associated with flight capability of D. citri. Our results may help explain dispersal behavior of D. citri with respect to practical management on an area-wide scale.

First report of the fungus Fomitiporia maxonii Murrill causing citrus wood rot in commercial orange and grapefruit groves in Cuba

Cuban citriculture has recently been affected by important pests and diseases including black citrus aphid Toxoptera citricida Kirkaldy, citrus leafminer Phyllocnistis citrella Stainton, Asiatic citrus psyllid Diaphorina citri Kuwayama, Citrus tristeza disease, and huanglongbing. This complex of ‘invasive species’ is thought to be contributing to the increasing decline of commercial citrus groves. During several surveys carried out in commercial citrus areas of several provinces in Cuba, symptoms of dieback, characterized by the presence of abundant dry branches and wood rot were detected on Criolla Valencia orange, Marsh grapefruit trees on sour orange, and Cleopatra mandarin rootstocks. Samples of branches and trunk wood were processed and a fungus was isolated from all samples. Morphological, physiological and molecular characterization demonstrated that the isolated agent is Fomitiporia maxonii Murrill. The incidence of affected trees was high in most surveyed groves, reaching 100% in old groves. Symptoms similar to the ones found in naturally infected trees were reproduced on trees inoculated with pure cultures of the fungus, and the fungus was recovered in culture from inoculated trees, thus fulfilling Koch's postulates. This is the first report of an association of F. maxonii with citrus wood rot in Cuba.

Comparison of DNA extraction methods for detection of citrus huanglongbing in Colombia

Four DNA citrus plant tissue extraction protocols and three methods of DNA extraction from vector psyllid Diaphorina citriKuwayama (Hemiptera: Psyllidae) were compared as part of the validation process and standardization for detection of huanglongbing (HLB). The comparison was done using several criterias such as integrity, purity and concentration. The best quality parameters presented in terms of extraction of DNA from plant midribs tissue of citrus, were cited by Murray and Thompson (1980) and Rodríguez et al. (2010), while for the DNA extraction from psyllid vectors of HLB, the best extraction method was suggested by Manjunath et al.(2008).

Prospective Analysis of the Geographic Distribution and Relative Abundance of Asian Citrus Psyllid (Hemiptera: Liviidae) and Citrus Greening Disease in North America and the Mediterranean Basin

The invasive Asian citrus psyllid (Diaphorina citri Kuwayama) is the vector of the bacterial pathogen (‘Candidatus Liberibacter asiaticus’) that is the putative causal agent of citrus greening disease (Huanglongbing disease) in citrus in many areas of the world. The capacity to predict the potential geographic distribution, phenology and relative abundance of the pest and disease is pivotal to developing sound policy for their management. A weather-driven physiologically based demographic model (PBDM) system was developed to summarize the available data in the literature, and used to assess prospectively the geographic distribution and relative yield of citrus, the relative densities of the psyllid, its parasitoid (Tamarixia radiata Waterston), and the potential severity of citrus greening disease in North America and the Mediterranean Basin. The potential for natural and biological control of citrus psyllid was examined prospectively.

Probing Behaviors of Adult Asian Citrus Psyllid (Hemiptera: Liviidae) are Not Appreciably Affected by Soil Application of Field-Rate Aldicarb to Citrus

In 2005, Huanglongbing disease (HLB), also known as citrus greening, was discovered in Florida. The presumptive causal agent of this disease is the phloem-limited bacterium ‘Candidatus Liberibacter asiaticus’ (Las) which is spread by the Asian citrus psyllid (Diaphorina citri Kuwayama). Following the discovery of HLB, insecticide use for control of the vector has increased dramatically. One such insecticide is aldicarb, a soil-applied systemic carbamate insecticide that has been used in Florida citrus since the 1970's for both control of insect and mite pests and for its potential plant growth promoting benefits. The objective of this study was to determine the effects of soil-applications of aldicarb to citrus on the feeding behavior of D. citri, including whether this systemic insecticide disrupts feeding behaviors responsible for Las transmission. To achieve this goal, an electrical penetration graph monitor was used to examine D. citri feeding behavior when given a feeding access period of 12 h on aldicarb-treated and untreated citrus plants. Results showed no reduction in D. citri probing behaviors between treatments, and no insects died during recordings. Unexpectedly, at the cohort level, both phloem salivation and phloem ingestion were significantly longer on aldicarb-treated compared with untreated plants, suggesting that aldicarb application may increase the likelihood of Las transmission. Although registration of aldicarb for use in the U.S. has been discontinued for the last year, it has been reregistered for use in certain crops that may include citrus in the future. Thus, there is renewed importance in understanding the effects of aldicarb and other insecticides applied to suppress insect-transmitted diseases.

Ants (Hymenoptera: Formicidae) Associated withDiaphorina citri(Hemiptera: Liviidae) and their Role in its Biological Control

After the arrival of the Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae) in Florida, several studies mentioned the presence of ants where D. citri was present, but there was no clarification of their specific interaction with the psyllid. The goal of this study was to elucidate the role of ants in the biological control of D. citri by observing ant behavior and by determining if ant presence, modified by exclusion manipulations, affected parasitism of D. citri by Tamarixia radiata (Waterston, 1922) (Hymenoptera: Eulophidae), an introduced parasitoid of the psyllid, when the insect was infesting orange jasmine, Murraya paniculata (L.) Jack (Sapindales: Rutaceae) and Persian lime, Citrus latifolia Tanaka (Sapindales: Rutaceae). During a preliminary survey on M. paniculata in Homestead, Florida, we observed 2 ant species in association with D. citri, i.e., the big headed ant, Pheidole megacephala Fabricius, and the rover ant, Brachymyrmex obscurior Forel. In 2 ant exclusion experiments, using a 2-cm-wide barrier of Tanglefoot®, P. megacephala was the only ant species found in M. paniculata while P. megacephala, B. patagonicus and Solenopsis invicta Buren were observed in C. latifolia. The number of P. megacephala found in the unprotected flushes in M. paniculata fluctuated between 0.15 and 0.5 per flush while in C. latifolia the number of ants, pooled across species, varied between 1.44 and 6.61. In M. paniculata flushes from Tanglefoot-treated plants, 20.36% of the nymphs were parasitized by T. radiata compared to 0.39% parasitism in untreated control flushes where ants had not been excluded. Fifty-eight percent of the psyllid nymphs were parasitized in the C. latifolia Tanglefoot® ant-exclusion flushes compared with 8.57% parasitism in the non-exclusion control. An additional experiment using the ant bait Extinguish Plus® (Hydramethylnon 0.365% S-Methoprene 0.250%) applied to the soil surrounding the trunk showed that the use of a granular bait can help to reduce ant populations and consequently increase the percentage parasitism of the Asian citrus psyllid.