Phloem-feeding insects, including the Asian citrus psyllid (Diaphorina citri), navigate one of the most osmotically challenging diets in nature, the sugar-rich phloem sap. Maintaining osmotic homeostasis is critical for survival, development, and vector competence, particularly in transmitting 'Candidatus Liberibacter asiaticus', the causal agent of citrus greening disease or huanglongbing (HLB). This review synthesizes current knowledge on the physiological, biochemical, and behavioral adaptations that enable D. citri to cope with extreme osmotic pressures. Key strategies include sucrose hydrolysis and conversion into glucose, fructose, and trehalose, as well as redistribution via the haemolymph, and efficient excretion of honeydew, which varies structurally and chemically across different developmental stages and sexes. These adaptations support prolonged phloem feeding, facilitate dual-lifestyle pathogen survival in both phloem and haemolymph, and directly enhance 'Ca. L. asiaticus' acquisition and transmission efficiency. HI also highlight honeydew as an indicator for feeding behavior, host suitability, and susceptibility to insecticides is also highlighted. Finally, emerging approaches to disrupt osmoregulation, including RNAi-mediated interference with sugar metabolism and water transport, which may provide innovative avenues for integrated management of D. citri and mitigation of HLB spread, will be discussed.

The Asian citrus psyllid, Diaphorina citri, transmits the putative causal agent of citrus greening disease, 'Candidatus Liberibacter asiaticus'. The transmission occurs in a propagative, circulative manner. Specific protein-protein interactions are required for the accomplishment of the transmission process. We employed the far-Western technique, also known as protein overlay assay, and mass spectrometry to identify D. citri proteins that specifically recognize membrane proteins of 'Ca. L. asiaticus'. Whole-body protein extracts of D. citri were separated by electrophoresis and blotted onto polyvinylidene difluoride membranes. The membranes were overlayed with sonicated leaf midrib extracts from 'Ca. L. asiaticus'-infected citrus plants. The protein complexes were detected using different antibodies against 'Ca. L. asiaticus' membrane proteins and peptidoglycans associated with lipoproteins. By comparison, spots were extracted from a polyacrylamide gel for liquid chromatography-tandem mass spectrometry analysis. Identified proteins included ATP synthase alpha and beta subunits, actin, alpha- and beta-tubulins, transitional endoplasmic reticulum ATPase TER94, 78 kDa glucose-regulated protein, and arginine kinase. These findings emphasize the involvement of energy machinery and muscle proteins in the 'Ca. L. asiaticus'-D. citri interactions. Understanding the pathogen-vector interactions will lead to better-designed control strategies based on the interference with specific interactions and/or blocking transmission.

'Candidatus Liberibacter asiaticus' (CLas), the causal agent of citrus huanglongbing, is transmitted by the Asian citrus psyllid Diaphorina citri. While CLas-positive (CLas+) females exhibit increased fecundity and metabolic demands, their neuroendocrine regulation mechanisms remain unclear. We propose CLas manipulates dopamine (DA) signaling to enhance psyllid fecundity and CLas proliferation. Metabolomics revealed elevated DA in CLas+ females. Silencing DA synthesis genes and receptor DcDop2 via RNAi reduced lipid reserves, fecundity, and ovarian CLas titers. Through combined in vivo and in vitro experiments, we demonstrated that the microRNA miR-31a suppresses DcDop2 expression by binding to its 3' untranslated region. Overexpression of miR-31a resulted in decreased DcDop2 expression and CLas titers in the ovaries, eliciting phenotypic defects akin to DcDop2 knockdown. Furthermore, DcDop2 knockdown and miR-31a overexpression reduced juvenile hormone (JH) levels and adipokinetic hormone (AKH) signaling in fat bodies and ovaries. Consequently, CLas regulates the DA-DcDop2 signaling axis to improve D. citri lipid metabolism and fecundity, while simultaneously promoting its replication. These findings reveal a coevolution between CLas proliferation and ovarian development in the insect host. This discovery enhances our understanding of the molecular interplay between plant pathogens and vector insects and offers novel targets and strategies for HLB field management.

Diaphorina citri Kuwayama (Hemiptera: Liviidae) vector bacteria (Candidatus Liberibacter asiaticus) that cause huanglongbing, an economically devastating disease of citrus. Management of D. citri infestations is primarily through insecticides, but alternative control methods remain under consideration including the co-opting and disruption of D. citri mating-duet vibrational communication signals. This study applies generative adversarial network and convolutional neural network methods to distinguish among female and male duetting signals when the sex of the signaler is not visually verifiable or when multiple male-female pairs are duetting. Up to 99% accuracy was achieved in identifying D. citri female and male signalers in experiments where standard statistical analyses fail to distinguish them at P < 0.05 statistical significance. Such knowledge has potential to increase mating disruption effectiveness by identifying signals to which females have greater preference. Although these studies were conducted only with D. citri, there is future opportunity to consider interference from communication signals produced when vibrational signals of multiple pest species are present and, combined with Internet of Things (IoT) technological capabilities, to further improve the capability for early detection and management of insect pests.

Juvenile hormone-regulated ribosomal protein DcRPS25 Mediates tolerance to Huanglongbing pathogen in the Vector Diaphorinacitri.

Insecticide applications are commonly recommended for managing Diaphorina citri, the vector of huanglongbing (HLB), but their effectiveness in reducing transmission of 'Candidatus Liberibacter asiaticus' (CLas), especially during continuous psyllid influx and shoot growth, remains unclear. This study evaluated the efficacy of foliar application of thiamethoxam and spinetoram in reducing CLas transmission in sweet orange seedlings. Two experiments were conducted up to 13 days after first spray. In experiment 1, CLas-positive psyllids were confined in seedlings every 2 days. Treatments were: control; S14, one spray at day 0; and S7, sprays at days 0 and 7. In experiment 2, psyllids were released for free choice within a screenhouse every 2 days. Treatments were: control, S14, S7, and S3, sprays at day 0 and every 3 days. Sprays on day 0 were over unfolded leaves (V2 stage). Psyllid mortality was assessed in experiment 1. Psyllid occupancy (percentage of seedlings with at least one psyllid) and abundance (number of psyllids per seedling) were assessed in experiment 2. After 6 months, seedlings were tested for CLas by qPCR. In experiment 1, cumulative psyllid mortality was higher in sprayed treatments than in the control for both insecticides, but HLB incidence was similar. In experiment 2, both psyllid occupancy and abundance decreased with shorter spray intervals, with the lowest HLB incidence in S3. These findings suggest that reducing spray intervals can limit CLas transmission during periods of shoot growth and continuous vector pressure. However, CLas transmission was not entirely prevented, highlighting the need for integrated, area-wide management strategies.

Individual protective covers (IPCs) are a new exclusion strategy used in young citrus groves to exclude Asian citrus psyllid (ACP), Diaphorina citri , the vector of the causal agent responsible for Huanglongbing (HLB), or citrus greening. Other strategies to manage ACP in commercial citrus include red-dyed kaolin and reflective groundcover; however, these tools have not been evaluated on residential citrus. In collaboration with extension agents and master gardener volunteers, the efficacy of the IPCs, red-dyed kaolin, and a modified version of reflective groundcover, called reflective donuts, were evaluated in young backyard citrus located in 8 counties and 10 different locations. The effect of these treatments on 14 variables, including arthropod pests (ACP, citrus leafminer, and spider mites), diseases (citrus canker, greasy spot, and HLB symptoms), and tree growth (flush count, canopy spread, canopy width, trunk circumference, and tree height) were assessed for 2 years. IPCs excluded ACP successfully during the first year of the study, but not the second. IPCs reduced leafminer infestation and HLB symptoms significantly compared with the other treatments in both years. At the end of the study, red-dyed kaolin and reflective donuts improved tree growth, but leafminer infestation and HLB symptoms were not reduced compared with control trees (i.e., sprayed with insecticide on a calendar basis). Spider mite webbing and canker symptoms stayed low throughout treatments, which differed from previous studies done in commercial plantings.

The Asian citrus psyllid, Diaphorina citri, vectors Candidatus Liberibacter asiaticus (CLas) that causes citrus greening disease, which has devastated global citrus production. Current management primarily relies on the application of synthetic chemical insecticides, resulting in the evolution of resistance among D. citri populations. CLas is ingested by D. citri while feeding on infected plants and subsequently interacts with the gut epithelial surface to establish infection. To determine the functional significance of abundant gut surface proteins in D. citri during CLas uptake, we used RNA interference (RNAi) to silence nine key gut surface protein genes. Following membrane feeding on double-stranded RNAs (dsRNAs), transcript levels were reduced by 20-51% in adults and 28-50% in nymphs at 72 h, with higher knockdown efficiencies of 41-63% in adults and 30-81% in nymphs by 120 h. Some dsRNA treatments increased D. citri mortality by approximately 20% over the control treatment, and two treatments reduced honeydew production indicative of reduced feeding consistent with disrupted gut function. Silencing of several individual proteins, including alkaline phosphatase, cadherin, cluster of calcium-transporting ATPase, croquemort and monocarboxylate transporter, reduced CLas uptake in nymphs and/or adults. Silencing of abundant gut surface proteins in D. citri limited CLas uptake, establishing a functional basis for RNAi-mediated suppression of pathogen uptake. While additional studies are needed to determine specific molecular interactions, these results identify gut surface proteins as promising targets for RNAi-based interventions to reduce CLas uptake by psyllids. © 2026 Society of Chemical Industry.

The economic impacts of Huanglongbing disease have prompted global surveillance of citrus psyllid vectors. While yellow sticky traps (YSTs) are widely used to detect pests such as the African citrus psyllid (Trioza erytreae) and the Asian citrus psyllid (Diaphorina citri), alternative methods may capture unique species and greater taxa richness and abundance, which could impact downstream species identification and diagnostics. We assessed psyllid richness and abundance across 4 sites within major citrus-growing regions of eastern Australia, and found that combining hand sampling with YSTs captured more species compared to light trapping and pan traps, but all sampling techniques collected unique taxa. Species were identified via an integrative taxonomy approach combining host plant data, morphology, and DNA sequences. We generated 196 cytochrome oxidase reference sequences from 87 species, 27 genera, and 5 families. Of these, 65 morphospecies and a described species were previously unrecorded in public DNA databases. This allowed us to build a baseline reference for eastern Australian native psyllids found around citrus orchard environments, thereby enhancing species-level molecular identification, and strengthening surveillance and biosecurity in Australia.

Complete genome characterization of Diaphorina citri picorna-like virus from China and a proposal for the new family Psylloidiviridae.

Psyllids harbour the obligate nutritional symbiont 'Candidatus Carsonella ruddii' (CaCr), yet complete CaCr genomes remain unevenly sampled across Psylloidea, limiting both comparative analysis and temporal inference. Here, seven complete CaCr genomes (165-174 kb) were assembled and annotated from psyllid hosts representing four families, including lineages for which genome-grade resources had previously been unavailable. We integrated whole-genome phylogenomics, pangenome analysis, fossil-calibrated relaxed-clock dating and quantitative PCR (based on 16S rRNA) screening of secondary symbionts. Across hosts, CaCr retained an extremely reduced, AT-rich (>82%) and gene-dense (>90% coding) genome architecture with a conserved core of 155 genes, while the accessory fraction was limited and lineage-specific. Most variable genes belonged to amino-acid metabolism or proteins of unknown function, suggesting differential erosion of peripheral functions around a stable translational and informational core. Phylogenomically, CaCr diversification broadly tracked deep host diversification, although the CaCr lineage from Diaphorina citri grouped with Triozidae-associated lineages rather than with other sampled Psyllidae. Using two host fossil-informed soft calibrations, we estimated that major CaCr divergences occurred mainly from the Paleogene to the Miocene, with crown diversification of Cacopsylla-associated CaCr at 15.95-18.99 Ma. In contrast to the stability of the primary symbiosis, secondary symbionts showed patchy host distributions: Wolbachia- and Arsenophonus-like lineages occurred in multiple hosts, 'Candidatus Profftella armatura' was restricted to D. citri, and no secondary symbiont was detected in Cacopsylla chinensis. These results provide a time-resolved comparative framework for CaCr evolution in psyllids and underscore the different evolutionary stability of primary and facultative associates.

Diaphorencyrtus aligarhensis parasitizes the Asian citrus psyllid (ACP), Diaphorina citri, the primary insect vector responsible for transmitting Huanglongbing (HLB), a severe citrus disease. Screening of appropriate reference genes is a critical prerequisite for reliable RT-qPCR analysis, which is essential for investigating the functions of target genes in D. aligarhensis across diverse experimental conditions. However, to date, no validated reference genes have been reported for this species. This study assessed seven housekeeping genes in D. aligarhensis under six conditions (developmental stage, body tissue, population, temperature, diet, and starvation) using five stability algorithms (geNorm, BestKeeper, NormFinder, RefFinder, and ∆Ct). The results identified the most suitable reference genes for specific experimental conditions: EIF5A and RPL32 for the developmental stage; RPL13 and H3 for population comparisons; RPS6 and GAPDH for different feeding diets; RPL32 and RPS6 for starvation; RPL7A and RPS6 for different body tissues (head, thorax, abdomen) and temperature gradients (5 °C, 15 °C, 25 °C, 35 °C). Furthermore, the expression profiles of HSP70 were markedly different when normalized to the most versus the least stable reference genes across body tissues, diets, starvation durations, and temperatures. Our findings establish the first set of RT-qPCR reference genes for D. aligarhensis, providing a useful foundation for functional genomics research on this biological control agent.

Citrus tree vigor is regulated mainly by the rootstock. It may affect vegetative flushes and the dispersal and infestation of Diaphorina citri (Asian citrus psyllid) within the orchard, contributing to the inoculation of the huanglongbing (HLB) bacterium. We conducted an experiment using the sweet orange cv. Hamlin grafted onto two rootstocks of contrasting vigor: the vigorous 'Sunki Tropical' mandarin and the dwarfing 'Flying Dragon' trifoliate orange. The study aimed to investigate the impact of these rootstocks on tree growth, vegetative flush dynamics, psyllid infestation and dispersal, HLB progression, yield, and fruit quality in a young orchard. Psyllid infestation was strongly associated with the presence of flushes in a given period. Trees on vigorous rootstocks exhibited profuse growth, larger canopies, and longer, more abundant flushes, offering greater resources for psyllid feeding and reproduction over time. In contrast, trees on dwarfing rootstocks had smaller canopies and fewer, shorter shoots (50% shorter than vigorous), resulting in reduced psyllid abundance for these trees as a host in our study. HLB progression was slower in dwarfed trees throughout the evaluation period; however, by 43 months after planting (MAP), disease incidence and severity increased, resulting in similar levels between treatments. Our findings indicate that dwarfing rootstocks have the potential to integrate management strategies to reduce psyllid populations and, consequently, HLB progression under strict control of the insect vector, even in areas with high disease incidence. Dwarfing rootstocks, such as 'Flying Dragon,' significantly restrict vegetative growth and flush development, thereby reducing available feeding and oviposition sites for psyllids, offering a promising component in integrated HLB management strategies by lowering vector populations and disease spread potential. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Controlling the Asian citrus psyllid (ACP), Diaphorina citri, is key to preventing spread of huanglongbing, a disease that has decimated citrus industries worldwide. One promising control method is the Sterile Insect Technique (SIT). This involves rearing large numbers of a target pest, sterilizing them using radiation, and releasing them into the field to compete with wild conspecifics for mating, ultimately suppressing population growth. The success of SIT is largely influenced by 3 factors: (i) ensuring released insects are sufficiently sterile such that mating between wild and sterile individuals yields no (or very few) offspring; (ii) ensuring the ratio of sterile to wild insects released (the overflooding ratio [OFR]) is sufficient to minimize the occurrence of mating between 2 wild individuals; and (iii) ensuring the released insects are competitive with respect to mating performance, dispersal, and longevity. Previously, we tentatively identified that a 320 Gy dose of X-ray radiation was required to sterilize ACP. Herein we investigate the impact of OFR on the growth of caged populations. Laboratory-cage experiments suggested that following sterilization with 240 or 320 Gy, a single release of ACP at OFRs of 10:1 and 15:1, could effectively suppress subsequent growth of ACP populations. To validate this finding under more natural conditions, we repeated the experiments using mature citrus trees held within field-cages. We found that a sterilizing dose of 320 Gy of X-ray radiation had the greatest impact in the field-cages, with an increase in the OFR from 10:1 to 15:1 showing only a marginal additional benefit.

Investigating the effects of sublethal pesticide doses on pest population succession and physiological metabolism is crucial for IPM and resistance delaying. This study evaluated sublethal effects of abamectin on Diaphorina citri using two-sex life tables, population modeling, and measurements of hormone levels, energy reserves, and gene expression to reveal its transgenerational impacts. Results showed dose-dependent and transgenerational effects: both F0 and F1 generations experienced prolonged development and reduced longevity under LC25/LC50 stress. Life-table parameters (r, λ, R0, GRR, T) declined, and the model predicted a sharp population decrease after 60 days (from 10,357 to 1711 and 372 individuals under LC25 and LC50, respectively). The findings indicated that abamectin suppresses population growth by delaying development and limiting adult recruitment. Following abamectin treatment, hormone levels (20E and JH) showed dynamic fluctuations with delayed peaks in the treated groups, while energy reserves (glycogen and triglycerides) were generally reduced. Vitellogenin gene expression was mostly suppressed, except for a transient increase in Vg-1 and Vg-A1 (LC25, day 9), whereas VgR was generally up-regulated except in the LC25 group. Both LC25 and LC50 treatments suppressed D. citri development and reproduction by disrupting hormone balance and energy metabolism, without inducing hormesis. These findings provide a theoretical basis for optimizing field application strategies and support the use of abamectin in IPM programs to reduce outbreak risk and delay resistance development.

Abstract Citrus yellow vein clearing virus (CYVCV) poses a significant threat to global citrus production and is rapidly spreading in citrus-growing regions, including China. While it is known that CYVCV can be transmitted through grafting and contaminated tools, its transmission by insect vectors in the field remains poorly understood. In this study, we conducted extensive field surveys from 2021 to 2023, detecting CYVCV in populations of Asian citrus psyllid, Diaphorina citri (Hemiptera: Liviidae), across Fujian Province. Laboratory experiments confirm that D. citri transmits CYVCV in a semipersistent manner, with the virus retained in the esophagus and foregut but absent from the salivary glands. Using infectious clones of CYVCV, we demonstrate efficient virus acquisition, retention, and transmission by D. citri , with transmission efficiency positively correlated with the duration of acquisition access periods. Furthermore, a fluorescence-fused CYVCV infectious clone allows for real-time visualization of viral localization in citrus plants and D. citri , confirming non-phloem-specific infection and stylet-mediated transmission. Our findings establish the semipersistent transmission of CYVCV by D. citri , which is also a well-known vector for the transmission of Candidatus Liberibacter asiaticus, a pathogen that causes Huanglongbing (HLB) and widespread devastation to the citrus industry globally.

Huanglongbing (HLB) is the most serious disease affecting citrus production worldwide, and its management relies on controlling its vector, Diaphorina citri. Although Tamarixia radiata (Waterston) is widely used in biological control programmes, Diaphorencyrtus aligarhensis (Shafee et al.) has been proposed as a complementary agent; both species were reported in Colombia in 2016, yet their interaction dynamics under local conditions remain poorly understood. This study evaluated the development, morphometry, and interaction patterns of both parasitoids under controlled rearing conditions using a shared host population. Three treatments were established: non-parasitised nymphs, nymphs exposed to D. aligarhensis, and nymphs exposed to T. radiata, with parasitoids allowed to oviposit for 24 h. Developmental duration and morphometric traits were recorded daily. T. radiata completed its life cycle in less time (~11.7 days) than D. aligarhensis (~14.4 days) and than non-parasitized nymphs (~17 days). Morphometric traits were consistent with previously reported ranges, and this study provides the first detailed characterisation of the immature stages of D. aligarhensis in Colombia. Particularly, events of multiparasitoidism and superparasitoidism were documented under standardised conditions, demonstrating that both species can exploit the same host simultaneously. These findings offer new insights into parasitoid interaction dynamics and establish a biological foundation for developing integrated biological control strategies against D. citri.

Abstract BACKGROUND Citrus production worldwide is severely impacted by a devastating disease known as citrus greening, or Huanglongbing (HLB). The phytopathogen causing HLB is transmitted between trees by the Asian citrus psyllid, Diaphorina citri , which acts as the primary vector. Currently, there is no cure for HLB, and management efforts primarily rely on the use of insecticides. However, there is a growing need for alternative, environmentally sustainable control methods, such as RNA interference (RNAi). RESULTS We investigated the impact of gene silencing on the mortality of D . citri by targeting two genes, vacuolar‐sorting protein/sucrose non‐fermenting protein 7 ( DcSnf7 ) and inhibitor of apoptosis 5 ( DcIap5 ). Gene silencing was initially assessed by delivering synthesized double‐stranded RNA (dsRNA) to D . citri through topical feeding. To further assess gene suppression in vivo , we used a virus‐induced gene silencing (VIGS) approach to deliver RNAi to psyllids via citrus plants. Suppressing DcSnf7 and DcIap5 individually resulted in elevated nymph mortality; however, the combined suppression of both genes using dual dsRNA treatment did not yield an additive effect. We modified the infectious Citrus tristeza virus (CTV‐T36) clone to individually and jointly carry the truncated genes, DcSnf7 and DcIap5 . Over two successive generations, D . citri reared on plants inoculated with CTV‐t Snf7 , CTV‐t Iap5 , or the combined construct CTV‐t Snf7 –t Iap5 exhibited increased mortality at all life stages, as well as significantly reduced fecundity and fertility, compared to insects reared on non‐infected or CTV‐wt‐inoculated control plants. In addition, these VIGS plants shortened the lifespan of D . citri . Notably, the dual construct CTV‐t Snf7 –t Iap5 consistently produced the most pronounced reductions in survival, fecundity, fertility, and longevity of D . citri across all experiments, exceeding the effects observed with either single‐gene construct. CONCLUSIONS Our results suggest that silencing key genes of D . citri using RNAi mediated by VIGS represents a promising control strategy that could play a role in HLB management. © 2026 Society of Chemical Industry.

Abstract The global citrus industry has been severely affected by huanglongbing (HLB), a citrus disease associated with the bacterium Candidatus Liberibacter asiaticus ( C Las), vectored by the Asian citrus psyllid. HLB symptoms are seen in the tree's canopy, fruit, and root systems, which include canopy dieback, increased fruit drop, lower fruit Brix, and reduced fine root growth. Eliminating HLB from trees is challenging, as no single method can completely control C Las. There has been an increase in research focused on finding ways to mitigate the effects of HLB. Oxytetracycline hydrochloride (OTC), an antibiotic used in citrus trunk injections, has been gaining attention in citrus growing regions like North America, South America, and South East Asia and Brazil. Research on OTC trunk injections has shown a reduction in HLB symptoms and bacterial titer; however, little is known about the interaction between OTC trunk injections, genotype, environmental stresses, and other biotic stress. Although there is a wealth of information on the HLB pathogen and its effects on trees, a succinct analysis has yet to be done to draw conclusions about whole tree effects across a range of geographies and demonstrate the broad effects of the use of OTC in an HLB environment.

Citrus huanglongbing (HLB), associated with the bacterium 'Candidatus Liberibacter asiaticus' and spread by the Asian citrus psyllid (Diaphorina citri; ACP), poses a significant threat to California's citrus industry. First identified in Los Angeles in 2012, HLB has since spread through residential areas across Southern California. A risk-based survey (RBS) model has been developed to improve HLB surveillance and intervention. Within this framework, model components change as HLB dynamics shift, requiring regular updates to maintain data accuracy and model reliability. Disease spread is influenced by natural factors, such as ACP establishment and confirmed HLB locations, as well as human-mediated factors like global mobility (travel introduction from HLB-infected countries), transportation of citrus materials, nurseries, packinghouses, farmers' markets, and proximity to private or otherwise inaccessible lands. Human-mediated risk factors account for approximately 26.3% (18.4 to 38.4%) of HLB incidence across different years, and natural causes predominantly explain the remaining 73.7% (61.6 to 81.7%). Notably, global mobility was crucial for early HLB detection in new areas, whereas ACP density strongly correlated with disease spread once established. A retrospective analysis from 2015 to 2022 evaluated the RBS model's performance, showing a predictive power of 88 to 97%, which confirms its validity for developing targeted interventions and early detection strategies in California.