Asian Citrus Psyllid Adults Research Articles

Confirmation of Candidatus Liberibacter asiaticus in Asian Citrus Psyllids and Detection of Asian Citrus Psyllids in Commercial Citrus in Georgia (U.S.A.).

The Asian citrus psyllid (ACP) is the vector of Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening or Huanglongbing (HLB), one of the most devastating citrus diseases worldwide. The citrus industry in Georgia (U.S.A.) is in the process of a rapid expansion, and based on experiences with HLB in Florida, there is great concern about the potential impacts of HLB on this emerging industry. Prior to 2023, ACP had been identified in residential citrus trees in isolated Georgia counties but little to no testing of psyllids for CLas had occurred. However, in 2023, one individual psyllid collected from Chatham County was confirmed positive for CLas by PCR and sequencing. Furthermore, during 2023, ACP adults and nymphs were identified for the first time in a Georgia commercial citrus grove. The finding of ACP in a commercial planting represents a significant risk for CLas dissemination, and thereby has the potential to stall the rapid expansion of Georgia's citrus industry. In the coming years, surveillance and testing of ACP from commercial groves will be essential for the early detection and management of HLB and its vector to reduce HLB spread within Georgia's commercial groves.

Development of a sterile insect technique as a control strategy for the Asian citrus psyllid: establishing the effect of sterilizing X-rays on fecundity, fertility, and survival.

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is a major pest of citrus due to its role as the vector of the bacterium that causes huanglongbing. In commercial citrus, ACP control currently relies on the application of insecticides, which may not be sustainable long-term, nor practical in urban areas. The sterile insect technique (SIT) is an alternative strategy in which large numbers of pests are reared, sterilized using radiation, and then released into the field to compete with wild individuals for matings, suppressing population growth. As a fundamental step toward the development of SIT for ACP, this study sought to identify the optimum radiation dose required to sterilize ACP without affecting their survival and mating capacity. Virgin adult ACP of both sexes were subjected to doses of X-ray irradiation ranging from 40 to 480 Gy, then paired with a nonirradiated mate and allowed to produce offspring. Fecundity was estimated as the number of eggs laid, and fertility as the proportion of those eggs that hatched. Females were more radio-sensitive than males, exhibiting a major drop in fecundity at even the lowest dose and 100% sterility at 80 Gy. In contrast, a fivefold higher dose (400 Gy) did not achieve complete sterility in males, with around 5% offspring survival. However, F1 progeny of males exposed to 320 Gy or higher were subsequently found to be 100% sterile. This confirmation of inherited sterility suggests that balancing the sterilizing effects of radiation against its mortality-inducing effects may warrant further evaluation.

Optimal dsRNA Concentration for RNA Interference in Asian Citrus Psyllid.

The Asian citrus psyllid (ACP) is a citrus pest and insect vector of "Candidatus Liberibacter asiaticus", the causal agent of citrus greening disease. Double-stranded RNA (dsRNA) biopesticides that trigger RNA interference (RNAi) offer an alternative to traditional insecticides. Standardized laboratory screening of dsRNA requires establishing the minimal effective concentration(s) that result in effective RNAi "penetrance" and trigger RNAi, resulting in one or more measurable phenotypes, herein, significant gene knockdown and the potential for mortality. In this study, knockdown was evaluated for a range of dsRNA concentrations of three ACP candidate genes, clathrin heavy chain (CHC), vacuolar ATPase subunit A (vATPase-A), and sucrose non-fermenting protein 7 (Snf7). Gene knockdown was quantified for ACP teneral adults and 3rd instar nymphs allowed a 48 h ingestion-access period (IAP) on 10, 50,100, 200, and 500 ng/µL dsRNA dissolved in 20% sucrose followed by a 5-day post-IAP on orange jasmine shoots. Significant gene knockdown (p < 0.05) in ACP third instar nymphs and adults ranged from 12-34% and 18-39%, 5 days post-IAP on dsRNA at 10-500 and 100-500 ng/µL, respectively. The threshold concentration beyond which no significant gene knockdown and adult mortality was observed post-48 h IAP and 10-day IAP, respectively, was determined as 200 ng/µL, a concentration indicative of optimal RNAi penetrance.

Uso de Acolchados Plásticos para Reducir Diaphorinia citri 1-Huanglongbing e Incrementar el Rendimiento de Lima Mexicana en el Trópico Seco de México

Huanglongbing (HLB) vectored by Asian citrus psyllid (Diaphorina citri) severely affects commercial plantations of Mexican lime (Citrus aurantifolia) in the dry tropic region of Mexico. Management of Huanglongbing is based on intensive use of agronomic practices such as irrigation, nutrition, pruning, and weed, insect pest, and disease control. During 2018 to 2022, the effect of black, white, aluminum, and green plastic mulches, a white polypropylene mesh (ground cover), and bare soil (traditional system), were evaluated on D. citri and incidence-severity (I-S) of Huanglongbing, and Mexican lime yields. Trees with all types of plastic mulch had less I-S during the first 13 months of the study (35 to 40% of affected foliage) compared to bare soil (74% of tree affected). Also, plots with plastic mulches had fewer Asian citrus psyllid adults (one to 16 insects/trap/week) as compared with bare soil (11 to 28 adults). Mulched treatments had a positive effect on fruit production. After 4 years, plots with white, aluminum, green, and black plastic yielded 41.6, 40.1, 39.6, and 34.9 t/ha. Bare soil yielded only 26.6 t/ha. The cost to install plastic mulches was $526/ha. Because of that, the plastics increased yields by 50-56% and the average price of Mexican lime fruit was about $600 per ton. This production system is an economically profitable alternative to the growers to coexist with Huanglongbing in the dry tropics of Mexico.

Candidatus Liberibacter asiaticus: An important factor affecting bacterial community composition and Wolbachia titers in Asian citrus psyllid.

Endosymbionts play crucial roles in various physiological activities within insect hosts. The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is an important vector for Candidatus Liberibacter asiaticus (CLas), a fatal pathogenic bacterial agent causing the disease Huanglongbing in the citrus industry. This study combines high-throughput sequencing of 16S ribosomal RNA amplicons to explore how CLas affects the bacterial community in different color morphs (blue, gray), genders, and tissues (cuticle, gut, mycetome, Malpighian tubule, ovary, and testis) of ACP. We found that there was no significant differences in the bacterial community diversity and CLas acquired ratio between the different color morphs and genders of ACP adults. However, acquiring CLas could promote the adult bacterial community's diversity and richness more than in the uninfected condition. The presence of CLas could increase the Wolbachia and unclassified_Enterobacteriaceae proportions more than in the uninfected condition. The bacterial community diversity in the CLas infected tissues of ovary and cuticle, was lower than the uninfected condition, but the richness of all tissues was not different between the infected and uninfected conditions. CLas could also change the bacterial structure in different tissues and make the bacterial relationship network simpler than it is in an uninfected condition. Furthermore, we used quantitative real-time PCR to assess the dynamic changes of Wolbachia in CLas uninfected and infected color morphs and tissues of ACP. The results showed that Wolbachia titers were significantly higher in CLas infected adults than in uninfected adults. In different tissues, the Wolbachia titers in the testis, ovary, and Malpighian tubule were higher than their uninfected counterparts. Our results provide essential knowledge for understanding the symbionts of the ACP and how CLas affects the bacterial community of the ACP.

Characterization of the Asian Citrus Psyllid-'Candidatus Liberibacter Asiaticus' Pathosystem in Saudi Arabia Reveals Two Predominant CLas Lineages and One Asian Citrus Psyllid Vector Haplotype.

In Saudi Arabia (SA), the citrus greening disease is caused by ‘Candidatus Liberibacter asiaticus’ (CLas) transmitted by the Asian citrus psyllid (ACP) Diaphorina citri. The origin and route(s) of the ACP-CLas pathosystem invasion in SA have not been studied. Adult ACP were collected from citrus trees in SA and differentiated by analysis of the mitochondrial cytochrome oxidase I (mtCOI) and nuclear copper transporting protein (atox1) genes. A phylogenetic analysis of the Wolbachia spp. surface protein (wsp) gene was used to identify the ACP-associated Wolbachia spp. A phylogenetic analysis of the atox1 and mtCOI gene sequences revealed one predominant ACP haplotype most closely related to the Indian subcontinent founder populations. The detection and identification of CLas in citrus trees were carried out by polymerase chain reaction (PCR) amplification and sequencing of the 16S rDNA gene. The CLas-integrated prophage genomes were sequenced, annotated, and used to differentiate CLas populations. The ML and ASTRAL trees reconstructed with prophages type 1 and 2 genome sequences, separately and concatenated, resolved two major lineages, CLas-1 and -2. The CLas-1 clade, reported here for the first time, consisted of isolates from SA isolates and Pakistan. The CLas-2 sequences formed two groups, CLas-2-1 and -2-2, previously the ‘Asiatic’ and ‘Floridian’ strains, respectively. Members of CLas-2-1 originated from Southeast Asia, the USA, and other worldwide locations, while CLas-2-2 was identified only in Florida. This study provides the first snapshot into the status of the ACP-CLas pathosystem in SA. In addition, the results provide new insights into the pathosystem coevolution and global invasion histories of two ACP-CLas lineages with a predicted center of origin in South and Southeast Asia, respectively.

Screening commercial entomopathogenic fungi for the management of Diaphorina citri populations in the Lower Rio Grande Valley, Texas, USA

Ten strains of entomopathogenic ascomycete fungi, sourced from commercial formulations of blastopore or conidiospore formulations, were tested in 14 different formulations in a primary acquisition/direct spray bioassay against adult Asian citrus psyllid (Diaphorina citri Kuwayama (Hemiptera: Liviidae)). The Cordyceps (Isaria) javanica Apopka 97-C (conidia) strain was used as the standard. A statistical ranking system was established in which top performing pathogenic strains were selected for further screening and eventual field trials. Modified Potter-type spray towers were utilized to deliver a range of doses of viable spores to adult D. citri in an aqueous spray consistent with the rate of spores per hectare often used in real-world spray applications. Mortality was assessed after a seven-day incubation period under controlled climate conditions reflecting those in the Lower Rio Grande Valley (LRGV) of Texas, USA. Of the 14 preparations, the strains Metarhizium anisopliae E9, C. fumosorosea Ifr9901, Beauveria bassiana ATCC 74040 and ANT-03, M. anisopliae ESALQ1037, and M. robertsii DWR2009, showed greater levels of mortality than the standard, Apopka 97-C, in the laboratory setting. Of those six, two (Ifr9901 and ANT-03) were selected for further evaluation based on efficacy, commercial availability, geographical registration, and market outlook on production.

Impact of Huanglongbing Pathogen Infection on the Amino Acid Composition in Both Citrus Plants and the Asian Citrus Psyllid.

The Asian citrus psyllid (ACP) Diaphorina citri is the main vector of the pathogen Candidatus Liberibacter asiaticus (CLas), which is the causal agent of citrus Huanglongbing disease. Feeding by both ACP nymphs and adults on host plants allows them to obtain nutrition. Therefore, the nutritional content within the plant phloem is of much importance for the development and reproduction of ACP. The infection by pathogenic microbiomes may affect the amino acid contents of their host plants and then indirectly affect the biology of sap-feeding insects. In this study, we investigated the amino acid contents and their proportions in both CLas-infected and CLas-free citrus plants, ACP adults, and also in honeydew produced by ACP nymphs. Results showed that infection by CLas had a large impact on the amino acid species and proportion in all the tested target plants, ACP adults, and in the honeydew of ACP nymphs. The content of total amino acids in CLas-infected citrus was much higher than that of CLas-free citrus. However, CLas infection significantly reduced the proportion of essential amino acids (EAAs) in these plants. When feeding on CLas-infected citrus plants, ACP adults absorbed less total amino acids than those adults feeding on healthy plants, but the proportion of EAAs was significantly higher when they fed on CLas-infected citrus plants. The proportion of EAAs also significantly increased in the honeydew secreted by ACP nymphs that fed on CLas-infected citrus plants. However, EAA detection in the honeydew of ACP nymphs indicated that the utilization rate of EAAs by CLas positive ACP nymphs was reduced. Our study has revealed that CLas infection significantly affects the contents, proportion, and utilization efficiency of different amino acids in citrus plants, ACP adults, and nymphs, leading to a developmental pattern of ACP that is more conducive to CLas transmission.

Protocol for Successful Transmission of 'Candidatus Liberibacter asiaticus' from Citrus to Citrus Using Diaphorina citri.

A protocol to successfully transmit the huanglongbing (HLB) pathogen, 'Candidatus Liberibacter asiaticus', between citrus plants by using the Asian citrus psyllid (ACP) and an alternative way to help growers control ACP are proposed. Best results were obtained when pathogen acquisition by adults reared on fully symptomatic 'Ca. Liberibacter asiaticus'-positive plants, latency, and inoculation occurred at ambient air temperatures ranging from 24 to 28°C and when a single infective adult ACP was confined for 7 days on soft, newly developing vegetative shoots (stages v2 to v4). No infection resulted from confinement of infective ACP adults on mature leaves (stage v6). Under the described conditions, single ACP adults could successfully transmit 'Ca. Liberibacter asiaticus' to an average of 56.5% (35 to 83%) of plantlets with v2 to v4 shoots growing in 0.3-liter tubes and to 80.5% (76 to 86%) of plants with v2 to v4 shoots growing in 4.7-liter pots. The use of single insects and plantlets reduces labor, space, and other resources necessary to undertake transmission tests. It also reduces time needed for transmission studies and should help accelerate research on HLB. The results were used to develop an index for favorability to infection (IFI) to determine orchard vulnerabilities to 'Ca. Liberibacter asiaticus'. The IFI is based on the heterogeneous population of new shoots that occurs on tree canopies and may offer alternative or complementary alternatives to the laborious and costly insect surveys currently used in most instances to determine threshold levels for insecticide applications.

Effects of the entomopathogenic fungus Clonostachys rosea on mortality rates and gene expression profiles in Diaphorina citri adults

Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), is a serious pest of citrus. The insect also transmits Candidatus Liberibacter asiaticus, the pathogen of a devastating citrus disease called Huanglongbing. Clonostachys rosea is a versatile fungus that possesses nematicidal and insecticidal activities. The effect of C. rosea against D. citri remains unclear. Here we examined the pathogenicity of C. rosea against D. citri adults. A mortality rate of 46.67% was observed in adults treated with 1 × 108 conidia/mL spore suspension. Comparative transcriptomic analyses identified 259 differentially-expressed genes (DEGs) between controls and samples treated with fungi. Among the DEGs, 183 were up-regulated and 76 down-regulated. Genes with altered expression included those involved in immunity, apoptosis and cuticle formation. Our preliminary observation indicated that C. rosea is virulent against ACP adults and has the potential as a biological control agent for ACP management in the field.

Asian citrus psyllid adults inoculate huanglongbing bacterium more efficiently than nymphs when this bacterium is acquired by early instar nymphs

The Asian citrus psyllid (Diaphorina citri) transmits the bacterium ‘Candidatus Liberibacter asiaticus’ (CLas), which causes huanglongbing (citrus greening) disease, in a circulative-propagative manner. We compared CLas inoculation efficiency of D. citri nymphs and adults into healthy (uninfected) citron leaves when both vector stages were reared from eggs on infected plants. The proportion of CLas-positive leaves was 2.5% for nymphs and 36.3% for adults. CLas acquisition by early instar nymphs followed by dissections of adults and 4th instar nymphs revealed that CLas bacterium had moved into the head-thorax section (containing the salivary glands) in 26.7–30.0% of nymphs and 37–45% of adults. Mean Ct values in these sections were 31.6–32.9 and 26.8–27.0 for nymphs and adults, respectively. Therefore, CLas incidence and titer were higher in the head-thorax of adults than in nymphs. Our results suggest that following acquisition of CLas by early instar D. citri nymphs, emerging adults inoculate the bacteria into citrus more efficiently than nymphs because adults are afforded a longer latent period necessary for multiplication and/or translocation of CLas into the salivary glands of the vector. We propose that CLas uses D. citri nymphs mainly for pathogen acquisition and multiplication, and their adults mainly for pathogen inoculation and spread.

New Traps Cut Off Citrus Greening Pests from Hiding Places

Adult Asian citrus psyllid, Diaphorina citri, carries the bacterium thought to be the causal agent of Huanglongbing in its salivary glands. As it feeds on citrus leaves, the psyllid transmits the bacterium to the tree. The result is yellowed leaves, bitter fruit, and eventual tree death. Researchers across the nation are struggling to end the scourge of citrus greening disease, also known as huanglongbing. The disease renders citrus fruit inedible and eventually kills entire orchards. In Florida alone, from 2012?2016 the disease caused production losses of $4.4 billion and eliminated about 7,900 jobs.

Control efficacy and joint toxicity of thiamethoxam mixed with spirotetramat against the Asian citrus psyllid, Diaphorina citri Kuwayama.

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is one of the most devastating pests in citrus orchards, and has caused huge economic losses worldwide. Chemical control is the most effective way for psyllid control. Herein, the toxicity of nine insecticides to ACP adults and the joint action of thiamethoxam + spirotetramat were determined by a topical application method in the laboratory; field plot experiments were conducted to evaluate the control efficacy of one self-made thiamethoxam + spirotetramat 40% suspension concentrate (SC) comparing with thiamethoxam 21% SC, spirotetramat 22.4% SC, tolfenpyrad 15% SC and bifenthrin 100 g/L emulsifiable concentrate against ACP using foliar sprays in 2018-2019. The highest toxicity to ACP adults was achieved by beta-cyfulthrin, bifenthrin, thiamethoxam and acetamiprid, with median lethal doses of 0.247 to 1.382 ng/adult at 24 h after treatment. High toxicity was observed by chlorpyrifos, spirotetramat and tolfenpyrad, but moderate toxicity by pyriproxyfen and buprofezin. For mixutres of thiamethoxam and spirotetramat, a 25:15 mass ratio showed the highest synergistic effect, with a co-toxicity coefficient (CTC) of 246.52; while a 10:30 mass ratio exhibited an additive effect, with a CTC of 109.84. Thiamethoxam + spirotetramat 40% SC at 60-80 mg/kg can effectively control ACP with a control efficacy of 72.92 to 99.29% during 3-30 days. Moreover, foliar sprays of all tested insecticides at the tested rates had no phytotoxic effects on citrus trees. A one-time foliar spray of thiamethoxam + spirotetramat 40% SC at 80 mg/kg could be recommended to control ACP during its infestation period in citrus groves.

High Prevalence of Pantoea in Diaphorina citri (Hemiptera: Liviidae): Vector of Citrus Huanglongbing Disease.

As an important insect vector, Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae) transmits the pathogen 'Candidatus Liberibacter asiaticus' (CLas) that is associated with citrus greening also known as Huanglongbing (HLB) disease. The bacterial endosymbionts have a potential role in shaping the host range of insect herbivores and their performance on different host plants, which might affect the endosymbiont distribution in insect populations. Here, we detected and characterized Pantoea endosymbiont in nymph and adult ACP specimens collected from Citrus reticulata Blanco and Cordia myxa L. plants. The phylogenetic tree constructed using endosymbiotic bacteria 16S ribosomal RNA sequences indicated that Pantoea sp. was closely related to Mixta calida, sharing about 98% identity and was grouped with other Mixta and Pantoea endosymbionts. Our findings showed 100% and 92.3% infection of Pantoea in adults while 61.5% and 90% infection of Pantoea in nymphs collected from C. reticulata and C. myxa plants, respectively. Understanding the interaction of endosymbiotic bacteria with ACP associated with host plants could be useful for developing an effective management strategy for both ACP and HLB disease.

Immuno-Ultrastructural Localization and Putative Multiplication Sites of Huanglongbing Bacterium in Asian Citrus Psyllid Diaphorina citri.

Huanglongbing, the most destructive citrus disease worldwide, is caused by the bacterium ‘Candidatus Liberibacter asiaticus’ (CLas) and is vectored by the Asian citrus psyllid (ACP). Very little is known about the form and distribution of CLas in infected psyllids, especially at the ultrastructural level. Here, we examined these aspects by transmission electron microscopy, combined with immunogold labeling. In CLas-exposed ACP adults, the CLas bacterial cells were found to be pleomorphic taking tubular, spherical, or flask-shaped forms, some of which seemed to divide further. Small or large aggregates of CLas were found in vacuolated cytoplasmic pockets of most ACP organs and tissues examined, including the midgut, filter chamber, hindgut, Malpighian tubules, and secretory cells of the salivary glands, in addition to fat tissues, epidermis, muscle, hemocytes, neural tissues, bacteriome, and walls of the female spermatheca and oviduct. Large aggregates of CLas were found outside the midgut within the filter chamber and between the sublayers of the basal lamina of the hindgut and Malpighian tubules. Novel intracytoplasmic structures that we hypothesized as ‘putative CLas multiplication sites’ were found in the cells of the midgut, salivary glands, and other tissues in CLas-exposed ACP. These structures, characterized by containing a granular matrix and closely packed bacterial cells, were unbound by membranes and were frequently associated with rough endoplasmic reticulum. Our results point to the close association between CLas and its psyllid vector, and provide support for a circulative-propagative mode of transmission.

Development and Field Validation of a Beta-cyfluthrin-Based 'Attract-and-Kill' Device for Suppression of Asian Citrus Psyllid (Hemiptera: Liviidae) on Residential Citrus.

An 'attract-and-kill' (AK) device was evaluated for suppression of adult Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), on residential citrus. The AK device, made from weather-resistant plasticized PVC, lured D. citri adults by simulating the color of citrus flush and killed them with beta-cyfluthrin. This study evaluated: 1) lethality of AK devices weathered up to 8 wk on residential citrus; 2) survival of psyllids caged with potted plants and AK devices; 3) psyllid suppression achieved by AK devices on individual dooryard trees. AK devices weathered for up to 8 wk remained lethal to psyllids. Greenhouse trials evaluated survival of adult psyllids caged for 4 d with orange jasmine plants that were: 1) treated with an (beta-cyfluthrin-infused) AK device; 2) treated with a blank (no insecticide) AK device; or 3) 'untreated' with no AK device. After 4 d, psyllid survival was on average 95% lower among adults exposed to plants with AK devices than adults exposed to untreated plants or plants with blank AK devices. Less than half of the adults exposed to plants with AK devices were alive after 1 d and nearly all were dead after 4 d. Deployment of 20 AK devices per tree provided significant psyllid suppression on infested lemon trees from winter to summer and reduced mean reproduction (cumulative eggs) by 91% and mean attack intensity (cumulative psyllid-days) of adults by 59% and nymphs by 53%. AK devices could be an effective control option for D. citri in urban areas.

2019–2020 Florida Citrus Production Guide: Asian Citrus Psyllid

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, was first detected in Florida in 1998 and has since become the key pest of citrus due to its role as vector of the pathogen that causes citrus greening disease, also known as huanglongbing (HLB). The HLB pathogen, Candidatus liberibacter asiaticus (Clas), is transmitted and spread by adult ACP but acquired primarily by nymphs. This 7-page fact sheet is part of the 2019–2020 Florida Citrus Production Guide. Written by Lauren Marie Diepenbrock, Jawwad Qureshi, Lukasz Stelinski, and Philip A. Stansly, and publsihed by the Entomology and Nematology Department, March 2019. CG097/CG097: 2022–2023 Florida Citrus Production Guide: Asian Citrus Psyllid (ufl.edu)

Hexaacetyl-chitohexaose, a chitin-derived oligosaccharide, transiently activates citrus defenses and alters the feeding behavior of Asian citrus psyllid

Plants have a perception system triggered by pathogen and pest signals to initiate defense. These signals include evolutionarily conserved molecules from microbes and insects termed pathogen/herbivore-associated molecular patterns (PAMPs/HAMPs). Here we showed that hexaacetyl-chitohexaose (HC), an oligosaccharide from chitin, a structural component in insect exoskeletons and fungi cell walls, upregulated defense-associated genes WRKY22, GST1, RAR1, EDS1, PAL1 and NPR2, and downregulated ICS1 at 1 h after HC treatment in Sun Chu Sha mandarin leaves. The effect was transient as defense gene transcriptional changes were not observed at 18 h after the treatment. Electrical penetration graph (EPG) recordings were used to study the feeding behavior of Asian citrus psyllid (ACP) following the HC treatment. ACP is the hemipteran vector of Candidatus Liberibacter asiaticus (CLas), the pathogen associated with huanglongbing (HLB). Adult ACP displayed reduced intercellular probing, reduced xylem feeding count and duration, and increased non-probing activity on HC-treated citrus compared to controls. During an 18-h recording, percentage for total duration of xylem ingestion, phloem ingestion, intercellular probing were lower, and the percentage of non-probing behavior was higher in HC-treated leaves than in controls. In host-selection behavior studies, HC treatment did not alter the attractiveness of citrus leaves under light or dark conditions. In addition, ACP feeding on HC-treated leaves did not show differences in mortality for up to 10 day of exposure. In summary, we report that HC induced a transient defense in citrus and an inhibitory effect on ACP feeding but did not affect host selection or the insect fitness under the tested conditions.

Survival and lifespan of Diaphorina citri on non-host plants at various temperatures

Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is the insect vector of Candidatus Liberibacter asiaticus (Las), the causal bacteria of the devastating citrus disease Huanglongbing (HLB). Many citrus orchards in China have been destroyed by HLB infection.The survival time of ACPs without food was related to the temperature they experienced. The longest survival time of adult ACPs was 5.93 ± 0.12 days when the mean temperature was approximately 12 °C. The shortest lifespan of ACP adults was 2.33 ± 0.12 days when the mean temperature on the test day was approximately 26 °C. Surprisingly, ACP could feed on herbaceous plants in the absence of preferred hosts. The most suitable weed species for the ACP was Solanum nigrum, with the longest survival time of 41 days for all individuals tested. The survival time of ACPs feeding on herbaceous plants was also related to temperature. The surviving 20% and 10% of ACP adults in the Solanum nigrum treatment showed no decline but slight improvement as compared with control in the fecundity.In conclusion, some ACPs may be able to live for a month or even longer in an orchard if suitable plants and temperatures are available. The Las-infected ACPs that can survive by feeding on herbaceous plants may be sources of Las infection in replanted orchards. The suggested time to replant citrus in groves that were previously infected with Las is summer to autumn, or it is recommended to leave the land idle for more than three months.

Fogging loads of California fresh citrus for control of Asian citrus psyllid, Diaphorina citri :

Contact insecticides are commonly applied as fogs to disinfest and disinfect spaces. Recently, these fogs have been adapted to treat commodity within the spaces, and much has been learned regarding the efficacy of this process. When considering fresh citrus in California, fogs are applied to control both insects and microbes. One insect pest, the Asian citrus psyllid (ACP), Diaphorina citri, is a quarantine pest in California and limiting its geographic distribution is a major goal of the California citrus industry. While a variety of phytosanitary measures can be used to control adult ACP once fruit is at a packing house, ultimately, a treatment must be developed to disinfest field-run fruit prior to its exiting the grove. High-pressure fogging with 1,100-L of an aqueous mixture containing 0.2% Evergreen® (6% pyrethrins & 60% piperonyl butoxide) and 0.5% (v/v) BreakThru® (polysiloxane surfactant) was explored in laboratory-, pilot-, and commercial-scale trials as an approach to disinfest a 48-bin trailer load of fresh citrus. Laboratory-scale studies were conducted to quantify, and subsequently model, insecticidal coverage as a function of temperature, surface area, droplet size, and fog volume. Results are discussed in the context of experimental variability across confirmatory trials and continued efforts to optimize the technical and economic feasibility of fogging as a postharvest control strategy.