Rapid Loss of Nutritional Symbionts in an Endemic Hawaiian Herbivore Radiation Is Associated with Plant Galling Habit.

Insect herbivores frequently cospeciate with symbionts that enable them to survive on nutritionally unbalanced diets. While ancient symbiont gain and loss events have been pivotal for insect diversification and feeding niche specialization, evidence of recent events is scarce. We examine the recent loss of nutritional symbionts (in as little as 1 MY) in sap-feeding Pariaconus, an endemic Hawaiian insect genus that has undergone adaptive radiation, evolving various galling and free-living ecologies on a single host-plant species, Metrosideros polymorpha within the last ∼5 MY. Using 16S rRNA sequencing, we investigated the bacterial microbiomes of 19 Pariaconus species and identified distinct symbiont profiles associated with specific host-plant ecologies. Phylogenetic analyses and metagenomic reconstructions revealed significant differences in microbial diversity and functions among psyllids with different host-plant ecologies. Within a few millions of years, Pariaconus species convergently evolved the closed-gall habit twice. This shift to enclosed galls coincided with the loss of the Morganella-like symbiont that provides the essential amino acid arginine to free-living and open-gall sister species. After the Pariaconus lineage left Kauai and colonized younger islands, both open- and closed-gall species lost the Dickeya-like symbiont. This symbiont is crucial for synthesizing essential amino acids (phenylalanine, tyrosine, and lysine) as well as B vitamins in free-living species. The recurrent loss of these symbionts in galling species reinforces evidence that galls are nutrient sinks and, combined with the rapidity of the evolutionary timeline, highlights the dynamic role of insect-symbiont relationships during the diversification of feeding ecologies. We propose new Candidatus names for the novel Morganella-like and Dickeya-like symbionts.

Functional responses of two species of predatory mites (Acari: Phytoseiidae) to eggs and first-instar nymphs of Bactericera Gobica Logniova (Homoptera: Psyllidae).

The goji berry psyllid, Bactericera gobica Logniova (Homoptera: Psyllidae), is one of the most important pests on goji berry plants (Lycium barbarum L.), whose fruits are widely used in traditional Chinese medicine and food. However, chemical control is still the predominant control strategy of this pest. Recently, two species of predatory mites, Neoseiulus setarius Ma, Meng & Fan and Neoseiulus barkeri Hughes were found to be associated with B. gobica in China. To assess their predation potential against B. gobica, the functional responses of these two phytoseiid species feeding on different densities (2, 4, 8, 12, 16, 24 and 32 individuals) of B. gobica eggs and 1st instar nymphs were compared at a temperature of 25ºC ± 1º C. Logistic regression analysis revealed that both predatory mite species exhibited type Holling-II functional responses on eggs and 1st instar nymphs of B. gobica, with the predation number increased for both predators as the density of prey increased. Overall, N. setarius consumed more prey compared to N. barkeri across all levels of prey densities. Meanwhile, the highest attack rate (α = 0.0283), the lowest handling time (Th = 1.1324 h prey- 1), and the highest estimated maximum predation rate (T/Th = 21.19 prey day- 1) were all observed for N. setarius fed with 1st instar nymphs of B. gobica. These findings suggest that it is worthy considering utilizing N. setarius and N. barkeri as candidate biocontrol agents of B. gobica, with N. setarius appearing to be a more effective predator than N. barkeri.

Candidatus Liberibacter: From Movement, Host Responses, to Symptom Development of Citrus Huanglongbing.

Candidatus Liberibacter spp. are fastidious α-proteobacteria that cause multiple diseases on plant hosts of economic importance, including the most devastating citrus disease: Huanglongbing (HLB). HLB was reported in Asia a century ago but has since spread worldwide. Understanding the pathogenesis of Candidatus Liberibacter spp. remains challenging as they are yet to be cultured in artificial media and infect the phloem, a sophisticated environment that is difficult to manipulate. Despite those challenges, tremendous progress has been made on Ca. Liberibacter pathosystems. Here, we first reviewed recent studies on genetic information of flagellar and type IV pili biosynthesis, their expression profiles, and movement of Ca. Liberibacter spp. inside the plant and insect hosts. Next, we reviewed the transcriptomic, proteomic, and metabolomic studies of susceptible and tolerant plant genotypes to Ca. Liberibacter spp. infection and how Ca. Liberibacter spp. adapt in plants. Analyses of the interactions between plants and Ca. Liberibacter spp. imply the involvement of immune response in the Ca. Liberibacter pathosystems. Lastly, we reviewed how Ca. Liberibacter spp. movement inside and interactions with plants lead to symptom development.

The transcriptome landscapes of citrus leaf in different developmental stages.

KEY MESSAGE: The temporal expression profiles of citrus leaves explain the sink-source transition of immature leaves to mature leaves and provide knowledge regarding the differential responses of mature and immature leaves to biotic stress such as citrus canker and Asian citrus psyllid (Diaphorina citri). Citrus is an important fruit crop worldwide. Different developmental stages of citrus leaves are associated with distinct features, such as differences in susceptibilities to pathogens and insects, as well as photosynthetic capacity. Here, we investigated the mechanisms underlying these distinctions by comparing the gene expression profiles of mature and immature citrus leaves. Immature (stages V3 and V4), transition (stage V5), and mature (stage V6) Citrus sinensis leaves were chosen for RNA-seq analyses. Carbohydrate biosynthesis, photosynthesis, starch biosynthesis, and disaccharide metabolic processes were enriched among the upregulated differentially expressed genes (DEGs) in the V5 and V6 stages compared with that in the V3 and V4 stages. Glucose level was found to be higher in V5 and V6 than in V3 and V4. Among the four stages, the largest number of DEGs between contiguous stages were identified between V5 and V4, consistent with a change from sink to source, as well as with the sucrose and starch quantification data. The differential expression profiles related to cell wall synthesis, secondary metabolites such as flavonoids and terpenoids, amino acid biosynthesis, and immunity between immature and mature leaves may contribute to their different responses to Asian citrus psyllid infestation. The expression data suggested that both the constitutive and induced gene expression of immunity-related genes plays important roles in the greater resistance of mature leaves against Xanthomonas citri compared with immature leaves. The gene expression profiles in the different stages can help identify stage-specific promoters for the manipulation of the expression of citrus traits according to the stage. The temporal expression profiles explain the sink-source transition of immature leaves to mature leaves and provide knowledge regarding the differential responses to biotic stress.

Targeted Early Detection of Citrus Huanglongbing Causal Agent 'Candidatus Liberibacter asiaticus' Before Symptom Expression.

Citrus Huanglongbing (HLB) is the most severe disease of citrus plants caused by 'Candidatus Liberibacter asiaticus' and transmitted by the insect vector Asian citrus psyllid (ACP). No effective curative measure is available against HLB. For citrus production areas without HLB or with low HLB disease incidence, removal of 'Ca. L. asiaticus' inoculum is critical to prevent HLB spread. Such a strategy requires robust early diagnosis of HLB for inoculum removal to prevent ACP acquisition and transmission of 'Ca. L. asiaticus'. However, early diagnosis of HLB is challenging, because the citrus trees remain asymptomatic for several months to years after 'Ca. L. asiaticus' transmission by ACP. In this study, we report a new method for targeted early detection of 'Ca. L. asiaticus' in cultivar Valencia sweet orange (Citrus sinensis) before HLB symptom expression. We take advantage of the fact that 'Ca. L. asiaticus' remains around the ACP feeding site immediately after transmission into the young flush and before flush maturation. ACPs secrete salivary sheaths at their feeding sites, which can be visualized using Coomassie brilliant blue staining owing to the presence of salivary sheaths secreted by ACP. Epifluorescence and confocal microscopy indicate the presence of salivary sheaths beneath the blue spots on ACP-fed leaves. Quantitative real-time polymerase chain reaction (PCR) and conventional PCR assays are able to detect 'Ca. L. asiaticus' in the ACP feeding surrounding areas as early as 2 to 20 days after ACP feeding. This finding lays a foundation to develop much-needed tools for early diagnosis of HLB before symptom expression, thus assisting 'Ca. L. asiaticus' inoculum removal and preventing HLB from spreading.

New Anatomical Evidence from the Male Asian Citrus Psyllid (Hemiptera: Liviidae) Invokes Controversy Over the Accepted Function of Some Male Reproductive Organs in Psylloidea.

Males of many Psylloidea are known to possess a characteristic structure at the functional hub of their reproductive apparatus, between afferent and efferent passage of seminal fluid. The structure is a squat, cylindrical endoskeleton consisting of two sections. Classical authors named them as 'sperm pump' and 'ejaculatory duct', based on superficial resemblance to a spring-loaded, thimble-shaped cylinder, encircled by smooth, vertical columns interpreted to be muscles which, when contracted, compress the cylinder and affect seminal fluid discharge. The discovery of numerous spherules of unknown composition and function in and around the columns of the Asian citrus psyllid male genitalia invoked rigorous scrutiny of the classical literature for evidence to support its claims, and determined that the grounds for vetting the structure as a sperm pump were fully teleological. This paper raises several objections to modern acceptance of this classical interpretation, presenting them as problematic, thought-provoking, and sometimes controversial anatomical features. The two sections are herein called 'drum' and 'spout'. As an endoskeleton, the sections are an invagination of the exoskeleton and therefore cannot receive seminal fluid into their hollow. A phallus is identified inside an aedeagal tube, indicating that it is the ejaculatory duct-the tube, drum, and spout are considered its housing. A sheath envelopes the drum and is directly continuous with the spout hypodermis, another problematical feature raising the question of whether it is detached from adherence to the drum cuticles. Also, there are four afferent tubes but only two openings in the drum to receive their seminal fluids.

Bactericera cockerelli vitellogenin-6 like, a vitellogenin without a direct reproductive function?

Vitellogenin-like proteins are members of the large lipid transfer proteins, a family of proteins involved in reproduction, lipid circulation and immune defences. In this study, we identified a new Bactericera cockerelli vitellogenin-like (Vg-like) transcript, and named it BcVg6-like based on its similarity to Acyrthosiphon pisum Vg6. In silico analyses predicted different conserved domains in BcVg6-like compared with the conventional Ba. cockerelli vitellogenin, BcVg1-like, previously described by our research group. Phylogenetic analyses determined that BcVg6-like clustered with Vg-like-B proteins and not the conventional vitellogenins involved in vitellogenesis. Also, the expression analyses showed differences in BcVg6-like transcript expression between 7-day-old males and 3- and 7-day-old females. BcVg6-like was not upregulated after exogenous application of juvenile hormone III, but its relative expression increased significantly in alimentary canals of adult females exposed to tomato plants infected by the bacterial plant pathogen 'Candidatus Liberibacter solanacearum'. Our results suggest that in Ba. cockerelli, both vitellogenin genes may have different functions: BcVg1-like is a conventional vitellogenin that conserved its ancestral function as an egg yolk precursor whereas BcVg6-like might have acquired a function in lipid and/or other molecule transport, and could potentially play a role in immune defence.

Global gene expression in two potato cultivars in response to 'Candidatus Liberibacter solanacearum' infection.

BACKGROUND: Transcriptomic analyses were performed to compare the molecular responses of two potato varieties previously shown to differ in the severity of disease symptoms due to infection by "Candidatus Liberibacter solanacearum" (Lso), the causative agent of Zebra Chip in potato. A factorial design utilizing the two varieties and psyllids either harboring Lso or without bacteria was used to discriminate varietal responses to pathogen infection versus psyllid feeding. Plant response was determined from leaf samples 3 weeks after infection. RESULTS: In response to Lso infection, 397 genes were differentially expressed in the variety Atlantic (most susceptible) as compared to 1027 genes in Waneta. Over 80% of the transcriptionally-changed genes were down-regulated in both varieties, including genes involved in photosynthesis or primary and secondary metabolism. Many of the Lso-responsive genes involved in stress responses or hormonal pathways were regulated differently in the two potato varieties. CONCLUSIONS: This study focused on the time point just prior to the onset of symptom development and provides valuable insight into the mechanisms of Liberibacter pathogenicity, especially the widespread suppression of plant gene expression, including genes involved in plant defenses.

Selection of reference genes for expression analysis in the potato psyllid, Bactericera cockerelli.

The selection of reference genes is a crucial step for quantitative real-time PCR analyses and increasingly the use of more than one reference gene for accurate and reliable normalization is being recommended. In this study, a set of six genes was selected and their stability was assessed in different life stages and female organs of Bactericera cockerelli harbouring or not the bacterial pathogen 'Candidatus Liberibacter solanacearum' (Lso) haplotype B. The stability of each gene was determined using the BestKeeper, NormFinder and GeNorm programs. These analyses identified elongation factor-1a, ribosomal protein subunit L5 and ribosomal protein subunit 18 as the most stable genes to analyse gene expression during the insect life stages irrespective of Lso presence; Lso haplotype B only affected their respective ranking. By contrast, a common set of normalizers could not be found amongst the different female organs tested (bacteriomes, alimentary canals and reproductive organs).

Digital Gene Expression Analysis of Ponkan Mandarin (Citrus reticulata Blanco) in Response to Asia Citrus Psyllid-Vectored Huanglongbing Infection.

Citrus Huanglongbing (HLB), the most destructive citrus disease, can be transmitted by psyllids and diseased budwoods. Although the final symptoms of the two main HLB transmission ways were similar and hard to distinguish, the host responses might be different. In this study, the global gene changes in leaves of ponkan (Citrus reticulata) mandarin trees following psyllid-transmission of HLB were analyzed at the early symptomatic stage (13 weeks post inoculation, wpi) and late symptomatic stage (26 wpi) using digital gene expression (DGE) profiling. At 13 wpi, 2452 genes were downregulated while only 604 genes were upregulated in HLB infected ponkan leaves but no pathway enrichment was identified. Gene function analysis showed impairment in defense at the early stage of infection. At late stage of 26 wpi, however, differentially expressed genes (DEGs) involved in carbohydrate metabolism, plant defense, hormone signaling, secondary metabolism, transcription regulation were overwhelmingly upregulated, indicating that the defense reactions were eventually activated. The results indicated that HLB bacterial infection significantly influenced ponkan gene expression, and a delayed response of the host to the fast growing bacteria might be responsible for its failure in fighting against the bacteria.

Parallel histories of horizontal gene transfer facilitated extreme reduction of endosymbiont genomes in sap-feeding insects.

Bacteria confined to intracellular environments experience extensive genome reduction. In extreme cases, insect endosymbionts have evolved genomes that are so gene-poor that they blur the distinction between bacteria and endosymbiotically derived organelles such as mitochondria and plastids. To understand the host's role in this extreme gene loss, we analyzed gene content and expression in the nuclear genome of the psyllid Pachypsylla venusta, a sap-feeding insect that harbors an ancient endosymbiont (Carsonella) with one of the most reduced bacterial genomes ever identified. Carsonella retains many genes required for synthesis of essential amino acids that are scarce in plant sap, but most of these biosynthetic pathways have been disrupted by gene loss. Host genes that are upregulated in psyllid cells housing Carsonella appear to compensate for endosymbiont gene losses, resulting in highly integrated metabolic pathways that mirror those observed in other sap-feeding insects. The host contribution to these pathways is mediated by a combination of native eukaryotic genes and bacterial genes that were horizontally transferred from multiple donor lineages early in the evolution of psyllids, including one gene that appears to have been directly acquired from Carsonella. By comparing the psyllid genome to a recent analysis of mealybugs, we found that a remarkably similar set of functional pathways have been shaped by independent transfers of bacterial genes to the two hosts. These results show that horizontal gene transfer is an important and recurring mechanism driving coevolution between insects and their bacterial endosymbionts and highlight interesting similarities and contrasts with the evolutionary history of mitochondria and plastids.

Synthesis and regulation of chlorogenic acid in potato: Rerouting phenylpropanoid flux in HQT-silenced lines.

Chlorogenic acid (CGA) is the major phenolic sink in potato tubers and can constitute over 90% of total phenylpropanoids. The regulation of CGA biosynthesis in potato and the role of the CGA biosynthetic gene hydroxycinnamoyl CoA:quinate hydroxycinnamoyl transferase (HQT) was characterized. A sucrose induced accumulation of CGA correlated with the increased expression of phenylalanine ammonia-lyase (PAL) rather than HQT. Transient expression of the potato MYB transcription factor StAN1 (anthocyanin 1) in tobacco increased CGA. RNAi suppression of HQT resulted in over a 90% reduction in CGA and resulted in early flowering. The reduction in total phenolics and antioxidant capacity was less than the reduction in CGA, suggesting flux was rerouted into other phenylpropanoids. Network analysis showed distinct patterns in different organs, with anthocyanins and phenolic acids showing negative correlations in leaves and flowers and positive in tubers. Some flavonols increased in flowers, but not in leaves or tubers. Anthocyanins increased in flowers and showed a trend to increase in leaves, but not tubers. HQT suppression increased biosynthesis of caffeoyl polyamines, some of which are not previously reported in potato. Decreased PAL expression and enzyme activity was observed in HQT suppressed lines, suggesting the existence of a regulatory loop between CGA and PAL. Electrophysiology detected no effect of CGA suppression on potato psyllid feeding. Collectively, this research showed that CGA in potatoes is synthesized through HQT and HQT suppression altered phenotype and redirected phenylpropanoid flux.

Psyllids in Natural Habitats as Alternative Resources for Key Natural Enemies of the Pear Psyllids (Hemiptera: Psylloidea).

The pear psyllids (Cacopsylla spp.; Psylloidea) comprise ~24 species of sap-feeding insects distributed in Europe, temperate Asia, and (as introductions) in the Americas. These pear-specialized insects are among the most damaging and difficult to control pests in orchards. Biological control increasingly is being used to replace or partially replace insecticidal management of pear psyllids. Many key natural enemies of pear psyllids regularly occur in non-orchard habitats on native plants. The presence of beneficial species both in orchard and non-orchard habitats (here referred to as "spillover") has prompted suggestions that native plants and their associated psyllids should be conserved as alternative resources for natural enemies of pear psyllids. The expectation is that the natural enemies will move from those habitats into psyllid-infested orchards. This review shows that psyllids in native habitats are important resources for several key predators and parasitoids of pear psyllids. These resources are critical enough that some beneficials exhibit an almost nomadic existence as they move between plant species, tracking the seasonal appearance and disappearance of psyllid species. In contrast, other natural enemies show minimal or no spillover between orchard and non-orchard habitats, which likely is evidence that they exhibit limited movement at best between orchard and non-orchard habitats. To show conclusively that spillover also indicates that a beneficial species disperses between native habitats and orchards requires difficult research on insect movement. This review concludes with a brief discussion of these difficulties and possible solutions.

Unravelling the Molecular Identity of Bulgarian Jumping Plant Lice of the Family Aphalaridae (Hemiptera: Psylloidea).

Psyllids (Hemiptera: Psylloidea) are plant sap-sucking insects whose identification is often difficult for non-experts. Despite the rapid development of DNA barcoding techniques and their widespread use, only a limited number of sequences of psyllids are available in the public databases, and those that are available are often misidentified. Here, we provide 80 sequences of two mitochondrial genes, cytochrome c oxidase I (COI) and cytochrome b (Cytb), for 25 species of Aphalaridae, mainly from Bulgaria. The DNA barcodes for 15 of these species are published for the first time. In cases where standard primers failed to amplify the target gene fragment, we designed new primers that can be used in future studies. The distance-based thresholds for the analysed species were between 0.0015 and 0.3415 for COI and 0.0771 and 0.4721 for Cytb, indicating that the Cytb gene has a higher interspecific divergence, compared to COI, and therefore allows for more accurate species identification. The species delimitation based on DNA barcodes is largely consistent with the differences resulting from morphological and host plant data, demonstrating that the use of DNA barcodes is suitable for successful identification of most aphalarid species studied. The phylogenetic reconstruction based on maximum likelihood and Bayesian inference analyses, while showing similar results at high taxonomic levels to previously published phylogenies, provides additional information on the placement of aphalarids at the species level. The following five species represent new records for Bulgaria: Agonoscena targionii, Aphalara affinis, Colposcenia aliena, Co. bidentata, and Craspedolepta malachitica. Craspedolepta conspersa is reported for the first time from the Czech Republic, while Agonoscena cisti is reported for the first time from Albania.

The jumping plant-lice (Hemiptera, Psylloidea) in Urban Green Spaces of Bogotá (Colombia), with descriptions of two new species and redescription of Mastigimascolombianus Burckhardt, Queiroz and Drohojowska.

In a survey of the arthropod fauna of 33 Urban Green Spaces (UGS) in Bogotá, Colombia, between 2017 and 2019, 21 species (3,825 specimens) of Psylloidea were collected. These represent all seven recognised families of jumping plant-lice and include seven species identified only to genus. The specimens, all adults, were collected on 30 plant species used for arborization in the UGS. Two species are described as new (Mastigimaslongicaudatus Rendón-Mera, Burckhardt & Vargas-Fonseca, sp. nov. and Leuronotaalbilinea Rendón-Mera, Burckhardt & Vargas-Fonseca, sp. nov.), one species is redescribed (Mastigimascolombianus Burckhardt, Queiroz & Drohojowska) and one species is recorded for the first time from Colombia (Calindatrinervis Olivares & Burckhardt). Among the seven species identified only to genus is an undescribed species of Melanastera, representing a genus not previously known from Colombia. Fourteen species found during the survey are probably native (66%) and seven (33%) adventive. Our findings highlight the significance of UGS for preservation of biological diversity and stress the importance of using native plants in urban landscape planning for the conservation of the native entomofauna.

Individual Protective Covers Improve Yield and Quality of Citrus Fruit under Endemic Huanglongbing.

The use of individual protective covers (IPCs) to protect newly planted citrus trees from Huanglongbing (HLB) infection is being widely adopted in Florida, an HLB-endemic citrus-producing area. It is known that IPCs positively influence most horticultural traits, increasing tree growth, flush expansion, and leaf size, enabling trees to sustain balanced carbohydrate metabolism by preventing Candidatus Liberibacter asiaticus (CLas) infection, and inducing higher leaf chlorophyll levels. This may result in more productive trees. However, as the tree grows, IPCs eventually are removed, typically between 2 and 3 years after their initial installation. Once IPCs are removed, trees become exposed to the Asian citrus psyllid (ACPs) and ultimately become infected. In this work, we covered Valencia sweet orange trees with IPCs for 30 months, until the trees entered fruit-bearing age. We investigated how the IPC protection of newly planted trees for 30 months influenced the fruit quality and yield of "Valencia" trees for three consecutive seasons after IPC removal compared to non-covered trees. The use of IPCs kick-started the newly planted citrus trees, resulting in higher yields and fruits with better internal and external quality. After 30 months of IPC protection, tree canopies were larger and denser, supporting more fruit per tree than non-protected trees for three consecutive seasons, even though by the end of the first season after IPC removal, the trees were HLB-positive. Tree height, scion diameter, canopy volume, and leaf area were significantly improved compared to non-covered trees. Additionally, fruit quality was significantly improved in the three seasons following IPC removal compared to non-covered trees. However, a decline in quality was measurable in fruit from IPC trees after the second harvesting season, with trees affected by HLB. Based on the results from this study, we conclude that the benefits from IPC protection may last for at least three consecutive seasons once trees enter the productive age, despite CLas infection within 12 months after IPC removal.

Multiple factors driving the acquisition efficiency of apple proliferation phytoplasma in Cacopsylla melanoneura.

Phytoplasmas are bacterial pathogens located in the plant's phloem that are responsible for several plant diseases and are mainly transmitted by phloem-sucking insects. Apple proliferation (AP) is an economically important disease associated with the presence of 'Candidatus Phytoplasma mali' which is transmitted by two psyllid species. While Cacopsylla picta is a vector in different regions, the vector efficiency of C. melanoneura varies between different populations. This species is considered the main AP vector in Northwestern Italy but plays a minor role in Northeastern Italy and other European regions. To investigate whether the psyllid and/or the phytoplasma subtype drive the phytoplasma acquisition in C. melanoneura, a phytoplasma acquisition experiment was set up using single mating couples of overwintered individuals from different psyllid populations and phytoplasma subtypes. All analyzed insect populations acquired phytoplasma, but with different efficiencies and concentrations. The main factors driving the acquisition were the phytoplasma subtype and its concentration in the leaves of the infected trees together with the psyllid lineage. The phytoplasma concentration in the psyllids was again influenced by the phytoplasma subtype, the psyllid lineage and the region of origin, whereas the phytoplasma concentration in the leaves and the psyllid haplotype defined with the cytochrome oxidase I gene had only a minor impact on the phytoplasma concentration. This is the first study evaluating the roles of both the psyllid haplotype and the phytoplasma subtype on the acquisition process and highlights the importance of C. melanoneura as an additional AP vector. Supplementary Information: The online version contains supplementary material available at 10.1007/s10340-023-01699-1.

Development of rapid, sensitive and non-radioactive tissue-blot diagnostic method for the detection of citrus greening.

Citrus huanglongbing (HLB or citrus greening) is one of the most devastating diseases of citrus worldwide. The disease is caused by Gram-negative, phloem-limited α-proteobacterium, 'Candidatus Liberibacter asiaticus', vectored by the psyllid, Diaphorina citri Kuwayama. Citrus plants infected by the HLB bacterium may not show visible symptoms sometimes for years following infection and non-uniform distribution within the tree makes the detection of the pathogen very difficult. Efficient management of HLB disease requires rapid and sensitive detection early in the infection followed by eradication of the source of pathogen and the vector. The polymerase chain reaction (PCR) based method is most commonly employed for screening the infected/suspected HLB plants and psyllids. This is time consuming, cumbersome and not practical for screening large number of samples in the field. To overcome this, we developed a simple, sensitive, non-radioactive, tissue-blot diagnostic method for early detection and screening of HLB disease. Digoxigenin labeled molecular probes specific to 'Ca. L. asiaticus' nucleotide sequences have been developed and used for the detection of the pathogen of the HLB disease. The copy number of the target genes was also assessed using real-time PCR experiments and the optimized real-time PCR protocol allowed positive 'Ca. L. asiaticus' detection in citrus samples infected with 'Ca. L. asiaticus' bacterium.

Division of labor within psyllids: metagenomics reveals an ancient dual endosymbiosis with metabolic complementarity in the genus Cacopsylla.

IMPORTANCE: Heritable beneficial bacterial endosymbionts have been crucial for the evolutionary success of numerous insects by enabling the exploitation of nutritionally limited food sources. Herein, we describe a previously unknown dual endosymbiosis in the psyllid genus Cacopsylla, consisting of the primary endosymbiont "Candidatus Carsonella ruddii" and a co-occurring Enterobacteriaceae bacterium for which we propose the name "Candidatus Psyllophila symbiotica." Its localization within the bacteriome and its small genome size confirm that Psyllophila is a co-primary endosymbiont widespread within the genus Cacopsylla. Despite its highly eroded genome, Psyllophila perfectly complements the tryptophan biosynthesis pathway that is incomplete in the co-occurring Carsonella. Moreover, the genome of Psyllophila is almost as small as Carsonella's, suggesting an ancient dual endosymbiosis that has now reached a precarious stage where any additional gene loss would make the system collapse. Hence, our results shed light on the dynamic interactions of psyllids and their endosymbionts over evolutionary time.

YOLO-SCL: a lightweight detection model for citrus psyllid based on spatial channel interaction.

Efficient and accurate detection and providing early warning for citrus psyllids is crucial as they are the primary vector of citrus huanglongbing. In this study, we created a dataset comprising images of citrus psyllids in natural environments and proposed a lightweight detection model based on the spatial channel interaction. First, the YOLO-SCL model was based on the YOLOv5s architecture, which uses an efficient channel attention module to perform local channel attention on the inputs in the recursive gated convolutional modules to achieve a combination of global spatial and local channel interactions, improving the model's ability to express the features of the critical regions of small targets. Second, the lightweight design of the 21st layer C3 module in the neck network of the YOLO-SCL model and the small target feature information were retained to the maximum extent by deleting the two convolutional layers, whereas the number of parameters was reduced to improve the detection accuracy of the model. Third, with the detection accuracy of the YOLO-SCL model as the objective function, the black widow optimization algorithm was used to optimize the hyperparameters of the YOLO-SCL model, and the iterative mechanism of swarm intelligence was used to further improve the model performance. The experimental results showed that the YOLO-SCL model achieved a mAP@0.5 of 97.07% for citrus psyllids, which was 1.18% higher than that achieved using conventional YOLOv5s model. Meanwhile, the number of parameters and computation amount of the YOLO-SCL model are 6.92 M and 15.5 GFlops, respectively, which are 14.25% and 2.52% lower than those of the conventional YOLOv5s model. In addition, after using the black widow optimization algorithm to optimize the hyperparameters, the mAP@0.5 of the YOLO-SCL model for citrus psyllid improved to 97.18%, making it more suitable for the natural environments in which citrus psyllids are to be detected. The experimental results showed that the YOLO-SCL model has good detection accuracy for citrus psyllids, and the model was ported to the Jetson AGX Xavier edge computing platform, with an average processing time of 38.8 ms for a single-frame image and a power consumption of 16.85 W. This study provides a new technological solution for the safety of citrus production.