Citri Populations Research Articles

Effects of Diaphorina citri Population Density on Daily Timing of Vibrational Communication Calls: Potential Benefits in Finding Forage.

Adult Diaphorina citri (ACP) use visual and chemical cues to locate young citrus flush shoots on which they forage and oviposit, and they use vibrational communication duetting calls as cues to help locate mates. For individual pairs, calling and mating usually peaks between 10:00 and 15:00. To explore whether call rates (calls/h) are affected by interactions with nearby conspecifics, rates were compared in small citrus trees on which either 5 or 25 ACP female and male pairs had been released at 17:00 for later recording from sunrise (06:00) to 22:00. Final ACP locations were noted 40 h after release. Call rates were similar in both treatments during normal mating hours. However, rates were significantly higher for low- than high-density treatments between 06:00 and 10:00, which suggests calling during this period may be affected by conspecific density. Both sexes aggregated on flush at both densities. We discuss the potential that ACP producing calls near sunrise, outside of normal mating hours, might benefit from gains in reproductive fitness in low-density contexts if they call not only to locate mates but also to locate preferred flush—in which case, co-opting of vibrations to disrupt both mating and foraging may be feasible.

Distribution, Phenology, and Overwintering Survival of Asian Citrus Psyllid (Hemiptera: Liviidae), in Urban and Grove Habitats in North Florida

Cold hardy citrus is an emerging industry in north Florida. However, it is under the threat of Candidatus Liberibacter asiaticus (CLas), the agent of the citrus disease huanglongbing. Distribution and phenology of the Asian citrus psyllid, Diaphorina citri (Kuwayama), the vector of CLas, was investigated over a 2-year sampling period in north Florida. Diaphorina citri was only found in backyard and ornamental citrus along the Gulf of Mexico, and was not observed in cultivated citrus groves during the 2 years (2017-2018) of the survey. Diaphorina citri population peaks occurred approximately 2 mo later than in central Florida with major population peaks occurring in July. The number of D. citri adults was significantly higher on CLas infected than uninfected citrus trees, whereas more nymphs were found on uninfected trees. Most D. citri were negative for CLas except in Franklin county where both infected trees and psyllids were found. We were able to find adult D. citri during all winter months, despite temperatures as low as -5.5°C. During two consecutive winters, we conducted experiments to determine D. citri cold hardiness by caging D. citri under ambient conditions in mid-November and assessing survivors in the following spring. In 2018, approximately 21%, of D. citri adults survived overwintering whereas 16% survived in 2019 despite lower temperature in 2018 than in 2019. As we are at the earliest stage of HLB infestation, management of D. citri and CLas in north Florida should focus on removal of CLas-infected trees to reduce the reservoir of pathogen.

Virulence of Purpureocillium lilacinum strain ZJPL08 and efficacy of a wettable powder formulation against the Asian citrus psyllid (Diaphorina citri)

The Asian citrus psyllid, Diaphorina citri Kuwayama, is one of the most destructive pests of citrus and the primary vector of Candidatus Liberibacter spp., which cause citrus Huanglongbing (HLB). Microbial insecticides based on entomopathogenic fungi are safer alternatives to chemical pesticides. They can mitigate the spread of HLB by suppressing D. citri populations in citrus groves. Purpureocillium lilacinum strain ZJPL08, previously isolated from D. citri cadavers, is highly pathogenic to D. citri. We determined the virulence of strain ZJPL08 conidial suspensions and the efficacy of a wettable powder formulation. The LC50 of strain ZJPL08 against D. citri at 7 d post-inoculation was 2.11 × 104 conidia/mL, and the LT50 of a 1.0 × 108 conidia/mL suspension was 3.14 d in the laboratory. Under the same conditions, the LC50 of the wettable powder was 1.39 × 104 conidia/mL, and the LT50 was 2.64 d. The corrected mortality caused by the 1500-times diluted solutions of strain ZJPL08 wettable powder in D. citri reached 86.67% at 7 d post-treatment and 100% at 14 d post-treatment under field conditions. Our study revealed that strain ZJPL08 infected D. citri by hyphae penetrating directly through the cuticle and into the body cavity and tissues. These findings show that P. lilacinum strain ZJPL08 has potential for the effective control of D. citri.

Molecular and genetic analysis of resistance to METI-I acaricides in Iranian populations of the citrus red mite Panonychus citri

The citrus red mite, Panonychus citri, is a major pest on citrus all around the world. Mitochondrial Electron Transport Inhibitors of complex I (METI-I) acaricides such as fenpyroximate have been used extensively to control P. citri populations, which resulted in multiple reports of METI-I resistant populations in the field. In this study, biochemical and molecular mechanisms of fenpyroximate resistance were investigated in P. citri. Seven populations were collected from Northern provinces of Iran. Resistance ratios were determined and reached up to 75-fold in comparison to a fenpyroximate susceptible population. Cross-resistance to two additional METI-I acaricides, pyridaben and tebufenpyrad, was detected. PBO synergism experiments, in vivo enzyme assays and gene expression analysis suggest a minor involvement of cytochrome P450 monooxygenases in fenpyroximate resistance, which is in contrast with many reported cases for the closely related Tetranychus urticae. Next, we determined the frequency of a well-known mutation in the target-site of METI-Is, the PSST subunit, associated with METI-I resistance. Indeed, the H92R substitution was detected in a highly fenpyroximate resistant P. citri population. Additionally, a new amino acid substitution at a conserved site in the PSST subunit was detected, A94V, with higher allele frequencies in a moderately resistant population. Marker-assisted back-crossing in a susceptible background confirmed the potential involvement of the newly discovered A94V mutation in fenpyroximate resistance. However, introduction of the A94V mutation in the PSST homologue of D. melanogaster using CRISPR-Cas9 did not result in fenpyroximate resistant flies. In addition, differences in binding curves between METI-Is and complex I measured directly, in isolated transgenic and wildtype mitochondria preparations, could not be found.

The Enemy is Outside: Releasing the Parasitoid Tamarixia radiata (Hymenoptera: Eulophidae) in External Sources of HLB Inocula to Control the Asian Citrus Psyllid Diaphorina citri (Hemiptera: Liviidae).

Huanglongbing (HLB), the most destructive citrus disease worldwide, was first recorded in Brazil in 2004, and since then, more than 50 million trees identified with this disease have been eliminated. The disease is managed mainly by controlling the psyllid vector Diaphorina citri Kuwayama, 1908 (Hemiptera: Liviidae). Although the presence of the insect in commercial citrus groves is low, HLB infection rates increase in areas bordering the groves. The disease is transmitted by psyllids from host citrus plants in areas outside the managed groves, such as abandoned or organic groves and residential trees, and from orange jasmine plants in urban settings. In order to provide information to support HLB control, this study evaluated the biotic and abiotic variables that affect the dynamics of D. citri populations after releases of the parasitoid wasp Tamarixia radiata (Waterston, 1922) (Hymenoptera: Eulophidae) in external sources of HLB inocula. The study was divided into two parts. After releasing the parasitoids in non-commercial areas, we determined the following: (a) the variables that significantly affected the number of nymphs collected on shoots in the same non-commercial area; (b) the variables that significantly affected the number of adult psyllids collected in a neighboring commercial citrus area. Our results indicated that the number of nymphs in external areas was affected only by the host plant and rainfall. However, periodic parasitoid releases significantly reduced the number of adult psyllids collected in the commercial area. The results indicate that the release of parasitoids in external sources of inocula has the potential to maximize actions for D. citri control, contributing to the reduction of psyllid populations in commercial areas. Consequently, this strategy may help to manage the disease infection without an increase in insecticide use.

Molecular Marker to Identify Diaphorina citri (Hemiptera: Liviidae) DNA in Gut Content of Predators.

Diaphorina citri Kuwayama is the vector of the pathogenic bacteria Candidatus Liberibacter spp., the causative agent of Huanglongbing (HLB), the most serious disease of citrus worldwide. Because predatory insects have been historically neglected in biological control programs for D. citri, the impact of generalist predators on D. citri population densities is little understood. A useful tool to evaluate the dynamics of predator-prey interactions is molecular analysis of predators' gut content. We constructed a specific molecular marker to detect D. citri DNA in the gut content of predator insects, for use in estimating the predation rate of field-collected predators in citrus orchards on D. citri. Bioassays of the DNA half-life detection time were carried out with two predatory species, the ladybird beetle Hippodamia convergens Guérin-Méneville and the lacewing Chrysoperla externa (Hagen). The D. citri DNA half-life detection time (DT50) was 6.11 h for H. convergens and 5.46 h for C. externa. One hundred and seven field-collected predators were used for gut-content analysis (52 larvae/adults of ladybirds and 55 larvae of lacewings). The assays showed that 17.3% of ladybirds but no lacewings tested positive for D. citri DNA. These results show that generalist predators can contribute to biological control of D. citri and should be considered for use in pest management programs in citrus orchards.

Cover Caption

Asian citrus psyllid, Diaphorina citri Kuwayama, is vector of the bacterial pathogens causing huanglongbing. It occurs as three distinct color morphs in nature. Our results indicate that decreasing insecticide susceptibility among D. citri populations caused by over‐spraying is associated with increasing levels of detoxifying enzyme groups. Furthermore, orange/yellow morphs of this insect are more susceptible than blue/green and gray/brown color morphs suggesting that cuticular melanization may be a mechanism associated with development of resistance in this insect (see pages 843–852). Photo provided Tonya R. Weeks.

Impact of the Temperature on the Phenology of Diaphorina citri (Hemiptera: Liviidae) and on the Establishment of Tamarixia radiata (Hymenoptera: Eulophidae) in Urban Areas in the Lower Colorado Desert in Arizona.

The invasive pest Diaphorina citri Kuwayama was first detected in Arizona in 2009. Since late 2013, the parasitoid Tamarixia radiata (Waterson), the main biocontrol agent of D. citri, has been released as part of a biological control program on citrus grown in urban areas of two western Arizona counties in the lower Colorado desert environment. Here we report a 3-yr survey aimed at evaluation of T. radiata releases on D. citri populations and assess the impact of the climate conditions on the phenology of D. citri and on the establishment success of T. radiata. We also monitored the phenology of D. citri as part of this assessment on different citrus host species. We show that the high summer temperatures in the Arizona desert halt the development of D. citri for about 3 mo every year which appears to have limited the establishment and impact of T. radiata. At survey sites distant from release areas the parasitism rates over the season ranged from 0 to 75% and on average peaked around 50% in 2016 but it was low or absent in 2015 and 2017, respectively. We discuss the consequences of this phenology of D. citri in the desert areas for the prospects of long-term establishment of T. radiata and the management of this key citrus pest.

Screening Sticky Cards as a Simple Method for Improving Efficiency of Diaphorina citri (Hemiptera: Liviidae) Monitoring and Reducing Nontarget Organisms.

Management of Diaphorina citri Kuwayama (Hemiptera: Liviidae) populations is one of the major strategies for reducing the spread and incidence of huanglongbing (HLB). HLB is putatively caused by Candidatus Liberibacter spp. (Rhizobiales: Phyllopbacteriaceae) that are transmitted to citrus by psyllid vectors. Diaphorina citri population monitoring is done to detect its presence and inform on management decisions. Various methods are used for detecting and estimating D. citri densities but trapping with yellow or lime-green sticky cards has proven to be the most effective method. These sticky cards rely on the color preference of adult D. citri, but many flying organisms are attracted to the same color spectrum as psyllids. Hence, in field situations, sticky traps are hampered by large numbers of bycatches of nontarget organisms and debris. Here, we described a method using a mesh laid on the surface of traps as a sift to catch mainly psyllids, while reducing bycatches. By filtering D. citri through this mesh, they can be counted more rapidly and accurately. Although mesh-covered traps captured 5-15% less D. citri relative to uncovered ACP traps, both types of traps statistically agreed on D. citri detection and population densities. The effectiveness of mesh-covered traps did not vary with season. In addition, mesh-covered traps eliminated >90% of nontarget organisms and allowed for quicker enumeration of D. citri. We expect this method will become an important component of redesigning integrated pest management programs in citrus groves by reducing unintended impacts of beneficial arthropods during large scale D. citri monitoring.

Effects of Ladybeetle, Harmonia axyridis, Foraging Trails on Behavior of Tamarixia radiata

The Asian citrus psyllid, Diaphorina citri, is a threat to citrus production because it transmits the bacterium, Candidatus Liberibacter asiaticus (CLas), which causes huanglongbing (HLB), also known as citrus greening. Insecticide use is the most common tactic for reducing D. citri populations. However, emerging concerns caused by frequent insecticide applications are insecticide resistance and indiscriminate elimination of beneficial organisms. Biological control can potentially contribute to D. citri management but the interactions occurring between natural enemies of this pest are poorly understood. Prominent natural enemies of D. citri in Florida, U.S. include the primary ectoparasitoid, Tamarixia radiata and several species of predacious ladybeetles, often including Harmonia axyridis. We investigated the behavioral response of T. radiata to trail semiochemicals deposited by ladybeetles (H. axyridis) while foraging. The total residence times of T. radiata were shorter on leaves containing H. axryidis trails than on untreated controls. Likewise, both parasitism and host feeding of D. citri nymphs were reduced on whole plants treated with H. axyridis trails as compared with unmarked controls. Wasp behavior was not affected by ladybeetle trail extracts as clearly when similarly treated detached leaves were presented in paired choice tests confined within 9 cm diameter Petri dishes. The results suggest that T. radiata detects predator trails as an indicator of areas where intraguild predators were present, and this information may be used by parasitoids for predator avoidance and decreased competition. The impact of intraguild competition between natural enemies of D. citri on overall biological control deserves further investigation.

Response of Diaphorina citri (Hemiptera: Liviidae) to volatiles characteristic of preferred citrus hosts

The Asian citrus psyllid, Diaphorina citri, is currently the most important pest of citrus worldwide because it vectors ‘Candidatus Liberibacter’ spp., the etiological agents of lethal Huanglongbing (HLB). Reduction of D. citri populations is a key component of HLB management. Identifying potential D. citri attractants, such as volatiles, could be useful for behavioral management of this insect. This could, for instance, enhance catches of adults on monitoring traps. The overall aim of this study was to investigate the response of D. citri to volatiles characteristic of preferred citrus hosts. An ancillary objective was to formulate a synthetic blend of volatiles based on preferred host odors that could enhance monitoring traps. Volatile collections of two preferred citrus species, Duncan grapefruit (Citrus paradise) and sweet orange (Citrus sinensis), were performed in aeration chambers and analyzed by gas chromatography-mass spectrometry. Based on the grapefruit volatile profile, a synthetic blend consisting in d-limonene (0.62 mg), methyl N-methylanthranilate (0.19 mg), β-ocimene (0.11 mg), β-elemene (0.02 mg), and β-caryophyllene (0.02 mg) was prepared in 9.9 mL of dichloromethane and evaluated for attractiveness, as well as the individual compounds, and compared with a positive control of natural volatiles collected from Citrus sinensis. Behavior of D. citri adults was evaluated in two-choice behavioral assays comparing response to lures with different combinations and dosages of the volatiles deployed on yellow sticky traps. Individually, neither d-limonene nor methyl N-methylanthranilate affected behavior of D. citri. However, these volatiles increased catches of D. citri, as compared with solvent control, when presented as components of the synthetic grapefruit blend, as did the natural citrus odor positive control. Importantly, catch of D. citri appeared to vary with the release rate of the identified grapefruit volatile blend, which was attractive at a 0.1 mg loading dosage, but repellent at a dosage only 1 log step higher.

Comparison of aerial conidia and blastospores from two entomopathogenic fungi against Diaphorina citri (Hemiptera: Liviidae) under laboratory and greenhouse conditions

ABSTRACTThis study compared the insecticidal activity of liquid culture-produced blastospores and solid substrate-produced aerial conidia of Beauveria bassiana GHA and Isaria fumosorosea ARSEF3581 strains against Diaphorina citri adults. Insects exposed to 107 propagules/ml in a spray residue contact leaf bioassay died within 6 days at 25°C, with no significant differences between fungal treatments. At higher concentrations (108 propagules/ml), I. fumosorosea conidia killed psyllids faster compared to its blastospore formulation, i.e. 4 versus 5 days, respectively. In greenhouse tests, the same treatments applied to infested citrus plants (2 × 106 spores/ml) all significantly reduced the number of nymphs compared with the untreated controls over 3 weeks; however, only I. fumosorosea blastospores significantly reduced the number of F1 adult psyllids when compared with controls. Similar results were observed in the follow-up greenhouse test, where I. fumosorosea blastospores were the most effective treatment overall, reducing D. citri populations by about 60% after 21 days; by contrast, imidacloprid killed almost 100% of psyllids within a week in both tests. Fewer psyllids exhibited mycosis in the greenhouse (i.e. ≈20 versus ≥ 87% in the laboratory). This is the first report comparing both conidial and blastospore formulations of B. bassiana and I. fumosorosea for the control of a psyllid pest. Field testing is required to determine how successful different spore formulations might be under various environmental conditions.

COPF: Citrus orchard perimeter fencing as a strategy for reducing Asian citrus psyllid (Hemiptera:Liviidae) infestation

AbstractCitrus grove colonization by the Asian citrus psyllid (Diaphorina citri) starts from border trees. This behaviour can be exploited by placing barriers along grove borders to prevent psyllid incursion and thwart population establishment and growth. We tested the effects of psyllid‐resistant mesh fencing along grove borders for season‐long control of D. citri populations. Deployment of sticky cards at different heights revealed that most D. citri (>99%) were collected on traps placed at or below 3.7 m along grove border. Thus, psyllid‐resistant mesh fencing (3.7 m in height) was installed along the eastern and southern borders of a 3‐year‐old grapefruit grove to protect against D. citri infestations, while the west and north edges were left unprotected. A similar adjacent grove with no border fencing served as untreated control. A reduction of 55%–98% of D. citri numbers was observed in the grove with border fences relative to the untreated control. D. citri density reductions were more pronounced on the sides with border fences suggesting that the observed effects were due to the mesh fencing. Thus, border mesh fencing as a standalone approach or coupled with other management strategies, such as border sprays, could be an effective psyllid management strategy. The season‐long benefits of border fences are not limited to D. citri population control, but also significant reductions of insecticide input and nontarget effects, thus substantially mitigating the risks of secondary pest outbreaks and ensuring the sustainability of D. citri management in citrus groves.

Spatiotemporal dynamics of citrus huanglongbing spread: a case study

Citrus huanglongbing (HLB) is a severe disease caused by ‘Candidatus Liberibacter asiaticus’ and vectored by Diaphorina citri. In commercial orchards, where the disease is controlled by removal of trees with symptoms and by frequent vector control, epidemics of HLB are mostly driven by primary infections from inoculum sources external to the orchard. It has been previously shown that the density of D. citri populations is usually higher around the edges than the inner sections of HLB‐affected citrus orchards. Consequently, diseased trees are also concentrated on the edges of orchards. However, there is a lack of quantitative data on HLB gradient dynamics over long periods of time. The objective of this study was to characterize temporal HLB progress and spatiotemporal gradient dynamics over six years in a large citrus farm where the disease was managed according to standard recommendations. Disease incidence and annual disease progress rates were higher at the citrus blocks closer to the edge than those located around inner sections of the farm. A decreasing logistic function provided a good description of the spatiotemporal dynamics of HLB gradients. A fixed slope of disease gradients was estimated over time and diseased trees were observed up to 1500 m from the orchard border. These results confirm that primary infection is the main factor for the progress of HLB epidemics in an orchard under the recommended three‐pronged system management. Therefore, HLB management should be intensified at the blocks located on the edges of the orchards and extended to external sources of inoculum.

Evaluation of the efficacy of neonicotinoid and pyrethroid insecticides in Diaphorina citri Kuwayama (Hemiptera: Liviidae) populations in Colombia

The Asian citrus psyllid Diaphorina citri is the insect vector of the disease known as huanglongbing (HLB), which is the most devastating disease of citrus crops in the world. The Asian citrus psyllid was officially reported in Colombia in 2007, and a national phytosanitary emergency was declared because of the presence of HLB in 2015. Two different experiments were carried out in two locations (Apulo and Jerusalén, Department of Cundinamarca) in Colombia to evaluate the effectiveness of neonicotinoid (clothianidin, imidacloprid and thiamethoxan) and pyrethroid applications (bifenthrin, deltamethrin and lambda cyhalothrin) on the control of D. citri populations (adults, nymphs and eggs) in ‘Tahiti’ lime trees established under tropical dry forest conditions. In the first experiment, trees were foliarly treated as follows: (1) untreated trees; (2) trees treated with 100 g ha-1 of imidacloprid; (3) trees treated with 60 g ha-1 of bifenthrin; (4) trees treated with 12.5 g ha-1 of deltamethrin and (5) trees treated with a co-formulation of 70 g ha-1 of a neonicotinoid (thiametoxan) and 53 g ha-1 of a pyrethroid (lambda cyhalothrin). In the second experiment, trees were treated with 100 g ha-1 of clothianidin. Foliar insecticide applications were carried out at 0 and 4 weeks after the initiation of treatments (WAT). In the first trial, the control presented a mean number of individuals per flush of ≈1.14, whereas the trees treated with neoinicotinoids and pyrethroids showed 50% fewer individuals (0.53-0.61). For the population of immatures, the number of nymphs was 2.25 nymphs per flush in the control, as compared to 0.82-1.22 individuals observed in the treatments with insecticides. The mean number of eggs was also between 80-100% higher in the control trees (2.37 individuals), as compared to the treated trees (1.14-1.78). In the second trial, the use of clothianidin showed a higher control of eggs. The results suggest that the rotation of neonicotinoids with pyrethroids can be a tool to reduce populations and delay resistance processes in D. citri in citrus trees established under tropical dry forest conditions in Colombia.

Potencial de Aclepias curassavica L. (Apocynaceae) en el control biológico de plagas


 
 
 Para conocer el potencial de Asclepias curassavica L. en el manejo de plagas, del 01 de enero al 28 de diciembre de 2012, se estableció un estudio en una plantación de limón “persa” Citrus latifolia en Emiliano Zapata, Villamar, Michoacán, México. Una sección (tratamiento) incluyó la planta A. curassavica y la otra se mantuvo sin esa especie (testigo). Muestreos semanales documentaron especies y número de depredadores, fitófagos, parasitoides, y niveles de parasitismo en áfidos. Toxoptera aurantii, Aphis spiraecola, Diaphorina citri y Phyllocnistis citrella, fueron las principales plagas. Sus mayores poblaciones ocurrieron en el segundo semestre del año y coincidieron con los principales periodos de brotación del cultivo. Los principales enemigos naturales observados en A. curassavica fueron las familias Coccinellidae, Syrphidae, Chamaemyiidae, Chrysopidae y el parasitoide Lysiphlebus testaceipes. Los Coccinellidos predominaron durante el primer semestre del año, mientras que los otros grupos fueron frecuentes durante todo el año. Los resultados muestran una reducción de 46.3% en las poblaciones de áfidos de los cítricos donde se establecieron Asclepias; sin embargo, las poblaciones de D. citri se incrementaron 77%. Probablemente el mayor biocontrol de áfidos favoreció la disponibilidad de nichos vacíos (brotes vegetativos) y consecuentemente las poblaciones del psílido. La amplia diversidad de enemigos naturales registrados en A. curassavica sugiere un alto potencial de la planta para utilizarse en la regulación y estabilidad de la entomofauna de los agroecosistemas, más que en el control de plagas específicas.
 
 

An Ecoinformatics Approach to Field-Scale Evaluation of Insecticide Effects in California Citrus: Are Citrus Thrips and Citrus Red Mite Induced Pests?

Experimental approaches to studying the consequences of pesticide use, including impacts on beneficial insects, are vital; however, they can be limited in scale and realism. We show that an ecoinformatics approach that leverages existing data on pesticides, pests, and beneficials across multiple fields can provide complementary insights. We do this using a multi-year dataset (2002-2013) on pesticide applications and density estimates of two pests, citrus thrips (Scirtothrips citri (Moulton [Thysanoptera: Thripidae])) and citrus red mites (Panonychus citri McGregor [Acari: Tetranychidae]), and a natural enemy (Euseius spp. predatory mites) collected from citrus groves in the San Joaquin Valley of California. Using correlative analyses, we investigated the long-term consequences of pesticide use on S. citri and P. citri population densities to evaluate the hypothesis that the pest status of these species is largely due to the disruption of natural biological control-i.e., these are induced pests. We also evaluated short-term pesticide efficacy (suppression of citrus thrips and citrus red mite populations immediately post-application) and asked if it was correlated with the suppression of Euseius predator populations. Although the short-term efficacy of different pesticides varied significantly, our dataset does not suggest that the use of citrus pesticides suppressed Euseius densities or worsened pest problems. We also find that there is no general trade-off between pesticide efficacy and pesticide risk to Eusieus, such that highly effective and minimally disruptive compounds were available to citrus growers during the studied time period.

An Evaluation of the Use of Calcium, Potassium and Silicon for the Management of Diaphorina citri Populations in Tahiti Lime Trees

The recent appearance of the disease known as huanglongbing (HLB) in Colombia has caused the demand for alternative control methods for Diaphorina citri (i.e., the disease vector). Specifically, the use of nutrients, such as calcium (Ca), potassium (K) and silicon (Si), may provide some degree of plant defense against herbivory. One set of experiments (in the form of two separate experiments) was conducted on two different farms in the municipality of Jerusalén to study the effects of foliar and soil applications of nutrients (Ca, K and Si) on controlling the population dynamics of Diaphorina citri. Tahiti lime trees were treated as follows: i) untreated trees (absolute control); ii) clothianidin at a dose of 50 g active ingredient per hectare (chemical control); iii) Ca, K and Si foliar applications (at doses of 3 mL, 3 g and 2 mL of the commercial compound used per liter of H2O, respectively); and iv) soil application of potassium nitrate and potassium silicate (1 kg of commercial fertilizer per tree). Foliar sprays were carried out at 0 and 4 weeks after treatment (WAT) began; meanwhile, soil fertilization occurred at the beginning of the trial (i.e., 0 WAT). The results showed that differences were observed only in adults at 7 WAT, and the foliar calcium and silicon applications resulted in the lowest number of individuals (i.e., 1.13 per flush) compared with untreated trees (i.e., 3.13 per flush). The foliar clothianidin, Ca, Si and K sprays also affected the total number of nymphs. Additionally, Tahiti lime trees treated with either silicon or insecticide had fewer eggs than did trees in the other treatments. The use of these mineral nutrients showed a similar efficacy when compared to clothianidin, indicating that these mineral nutrients can enhance plant resistance. These observations suggest that foliar applications of K, Ca and Si could be considered as complementary tools within an integrated management program for D. citri in Colombia.

Genetic variation and potential coinfection of Wolbachia among widespread Asian citrus psyllid (Diaphorina citri Kuwayama) populations.

Wolbachia can profoundly influence the survival, reproduction, and defenses of insect hosts. These interactions could potentially be harnessed for managing pests or insect‐transmitted diseases. Diaphorina citri Kuwayama is a phloem‐feeding pest capable of transmitting the putative causal agent of citrus greening, Candidatus Liberibacter asiaticus (CLas). Like many insects, D. citri is also infected with Wolbachia (wDi). Recent studies indicate that the relative abundance of wDi could be associated with the abundance of CLas, and that wDi may contribute to regulating expression of phage lytic cycle genes in CLas, suggesting the need for better understanding of wDi biology in general. This study investigated the genetic diversity of wDi among D. citri in populations spanning eleven countries and two U.S. territories. Six Wolbachia genes, wsp, coxA, fbpA, ftsZ, gatB, and hcpA, were sequenced and compared across samples. Two prevalent wDi strains were identified across the samples, and screening of clone libraries revealed possible coinfection of wDi strains in specific populations. D. citri mitochondrial cytochrome oxidase subunit I gene (mtCOI) were more divergent between D. citri populations that were infected with different wDi strains or had different infection statuses (single infection vs. coinfection). While we could not eliminate the possibility that maternal transmission may contribute to such patterns, it is also possible that wDi may induce cytoplasmic incompatibility in their host. These findings should contribute to the understanding of wDi population ecology, which may facilitate manipulation of this endosymbiont for management of citrus greening disease worldwide.

Biofunctional analysis of Vitellogenin and Vitellogenin receptor in citrus red mites, Panonychus citri by RNA interference

Panonychus citri is one of the most damaging pests of horticultural crops. Conventional control of this pest population through pesticides has led to the enhanced pest resistance. Management of P. citri population through RNAi, is still largely unknown. In oviparous organisms, fabrication and development of yolk protein play a vital role in the reproduction. Vitellin (Vn) is the source of eggs storage that helps in proper functioning of Vitellogenin (Vg) and Vitellogenin receptor (VgR). VgR is very compulsory protein for the development of Vg into oocytes. In the current study, Vg (PcVg) and VgR (PcVgR) genes were studied and their expressions at different developmental stages were quantified by RT-qPCR. Females treated with dsRNA of PcVg and PcVgR genes exhibited reduction in gene expression. Down regulation of target genes significantly effected oviposition and reduced the egg laying capacity up to 48% as compared to control (ds-egfp). Synergistic effect of target gene’s dsRNA was also accessed that reduced the egg laying up to 60.42%. Furthermore, combination of target dsRNA on deutonymph and protonymph also resulted in 67% and 70% reduction in eggs, respectively. Synergistic effect of dsRNA at 1000 ng/ul resulted in longer life span as compared to control treatments. This study suggests to develop a new strategy of P. citri population control by reducing its reproduction.