Psyllid Species Research Articles

Gene expression profiling of Cacopsylla pyricola (Hemiptera: Psyllidae) infected with Ca. Phytoplasma pyri (Acholeplasmatales: Acholeplasmataceae) reveals candidate effectors and mechanisms of infection.

Phytoplasmas can negatively or positively alter vector host fitness. "Candidatus Phytoplasma pyri," is the causal agent of pear decline in commercial pear (Pyrus communis L.; Rosales: Rosaceae) and peach yellow leafroll in peach [Prunus persica (L.); Rosaceae]. This plant pathogen is transmitted by several species of pear psyllids (Cacopsylla spp. Hemiptera: Psyllidae). We sought to explore the relationship between the pear decline phytoplasma and its US vector, Cacopsylla pyricola (Förster), at the molecular genetic level through transcriptomic analysis using RNA-sequencing methodology. We also focused on phytoplasma and insect effectors, which are secreted proteins that can modulate interactions within a pathosystem. In this study, we identified 30 differentially expressed genes, 14 candidate insect effector genes, and 8 Ca. Phytoplasma pyri candidate effectors. Two strains of Ca. Phytoplasma pyri were identified based on immunodominant membrane protein sequence analysis from C. pyricola collected in the Pacific Northwest agricultural region. Here, we present a first genetic look at the pear decline pathosystem and report gene candidates for further exploration of infection mechanisms and potential tools for integrated pest management.

An annotated checklist with a key to the genera of Australian psyllids (Hemiptera: Sternorrhyncha: Psylloidea)

The diversity of the psyllids of Australia reflects that of the plants of this country, with large radiations and ecological dominance of Myrtaceae (e.g., Eucalyptus), Fabaceae (e.g., Acacia), Casuarinaceae (e.g., Allocasuarina, Casuarina) and Scrophulariaceae (e.g., Eremophila, Myoporum). Within Australian ecosystems, psyllids are critical components of food webs, especially with respect to providing energy-rich resources for many species of birds and insects and, historically, humans. Furthermore, in horticulture, agriculture and forestry, some Australian psyllid species are considered pests, causing leaf senescence and ‘dieback’, leaf deformation and inducing growth of sooty mould, with some adventive species capable of acting as vectors of plant pathogens. Several species are considered beneficial, having been introduced as biological control agents of weeds. Additionally, some Australian psyllids have established in other countries, or in regions within Australia that are not within their natural range; while others have such limited geographical ranges that they are of conservation concern. Here we provide an updated checklist of the species of Psylloidea present in Australia and updated a previous key to their genera based on adult morphology. This is the first checklist of the Australian psyllids compiled since the most recent global taxonomic classification, and provides detailed information on biogeographical, ecological and anthropogenic aspects, including global distribution, host plant data, pest status, conservation status, parasitoids, predators, and biological control programs. Our checklist includes information on 66 genera and 450 species, 414 formally described and 36 awaiting descriptions. This represents an increase of almost 20% of species since the last published checklist of 2004, which reported 354 described and 21 undescribed taxa. Additionally, we summarise the available information on more than 150 undescribed taxa. Finally, we reported here more than 60 new records, between distributions and host plant associations.

Differential expression of “Candidatus Liberibacter solanacearum” genes and prophage loci in different life stages of potato psyllid

Psyllid species, including the potato psyllid (PoP) Bactericera cockerelli (Sulc) (Triozidae) serve as host and vector of “Candidatus Liberibacter spp.” (“Ca. Liberibacter”), which also infects diverse plant hosts, including citrus and tomato. Psyllid transmission of “Ca. Liberibacter” is circulative and propagative. The time of “Ca. Liberibacter” acquisition and therefore vector life stage most competent for bacterial transmission varies by pathosystems. Here, the potato psyllid-“Ca. Liberibacter solanacearum” (CLso) pathosystem was investigated to dissect CLso-prophage interactions in the tomato plant and PoP-psyllid host by real-time quantitative reverse transcriptase amplification of CLso genes/loci with predicted involvement in host infection and psyllid-CLso transmission. Genes/loci analyzed were associated with (1) CLso-adhesion, -invasion, -pathogenicity, and -motility, (2) prophage-adhesion and pathogenicity, and (3) CLso-lysogenic cycle. Relative gene expression was quantified by qRT-PCR amplification from total RNA isolated from CLso-infected 1st–2nd and 4th–5th nymphs and teneral adults and CLso-infected tomato plants in which CLso infection is thought to occur without SC1-SC2 replication. Gene/loci expression was host-dependent and varied with the psyllid developmental stage. Loci previously associated with repressor-anti-repressor regulation in the “Ca Liberibacter asiaticus”-prophage pathosystem, which maintains the lysogenic cycle in Asian citrus psyllid Diaphorina citri, were expressed in CLso-infected psyllids but not in CLso-infected tomato plants.

The First Three Mitochondrial Genomes for the Characterization of the Genus Egeirotrioza (Hemiptera: Triozidae) and Phylogenetic Implications.

(1) Background: Mitochondrial genomes are important markers for the study of phylogenetics and systematics. Triozidae includes some primary pests of Populus euphratica. The phylogenetic relationships of this group remain controversial due to the lack of molecular data. (2) Methods: Mitochondria of Egeirotrioza Boselli were sequenced and assembled. We analyzed the sequence length, nucleotide composition, and evolutionary rate of Triozidae, combined with the 13 published mitochondrial genomes. (3) Results: The evolutionary rate of protein-coding genes was as follows: ATP8 > ND6 > ND5 > ND2 > ND4 > ND4L > ND1 > ND3 > APT6 > CYTB > COX3 > COX2 > COX1. We reconstructed the phylogenetic relationships of Triozidae based on 16 triozid mitochondrial genomes (thirteen ingroups and three outgroups) using the maximum likelihood (ML) and Bayesian inference (BI) approaches. The phylogenetic analysis of the 16 Triozidae mitochondrial genomes showed that Egeirotrioza was closely related to Leptynoptera. (4) Conclusions: We have identified 13 PCGs, 22 tRNAs, 2 rRNAs, and 1 control region (CR) of all newly sequenced mitochondrial genomes, which were the mitochondrial gene type in animals. The results of this study provide valuable genomic information for the study of psyllid species.

A Novel Interaction of Nesidiocoris tenuis (Hemiptera: Miridae) as a Biological Control Agent of Bactericera cockerelli (Hemiptera: Triozidae) in Potato.

Nesidiocoris tenuis (Hemiptera: Miridae) is a generalist predator commonly used to control the whitefly Bemisia tabaci in Europe. This mirid has been found and established in South Texas, where it was initially observed feeding on nymphs of the psyllid Bactericera cockerelli (Hemiptera: Triozidae) in open tomato fields. B. cockerelli is the vector of the fastidious bacterium "Candidatus Liberibacter solanacearum" that causes diseases in several solanaceous crops, including zebra chip (ZC) disease in potatoes. There is a need to better understand how this predator impacts the control of important crop pests, such as potato psyllids. We assessed the interactions between N. tenuis and B. cockerelli in three different environmental settings. First, we estimated the numeric response of N. tenuis preying on B. cockerelli under laboratory and greenhouse conditions. Second, we evaluated the predator-prey interaction under controlled field cage conditions. Then, we exposed N. tenuis under controlled field release conditions to the natural occurrence of B. cockerelli. Finally, we assessed the compatibility between the use of N. tenuis as a biological control agent in a field study and its impact on ZC disease incidence, severity in potato tubers, and potato yield. Laboratory and greenhouse experiments resulted in diverse types of functional model responses, including exponential and linear mathematical models. Our findings revealed a significant predation effect exerted by N. tenuis, resulting in a reduction of more than fourfold in the number of B. cockerelli nymphs per cage. Specifically, the nymphal population decreased from 21 ± 3.2 in the absence of N. tenuis to 5 ± 1.6 when N. tenuis was present. Furthermore, the combination of N. tenuis with a reduced insecticide program increased potato yields, but only reduced ZC tuber incidence in one of two potato cultivars evaluated, and in one season. Findings from these studies indicate that N. tenuis could be effective as a biological control agent for B. cockerelli in potato production in South Texas. This is the first report of N. tenuis preying on immature stages of any psyllid species.

Spanioneura fonscolombii Förster (Hemiptera: Psylloidea) a New Jumping Plant-Lice for Turkish Fauna

Aim of study: To investigate the distribution area, some biological characteristics and host plant relationship of Spanioneura fonscolombii Förster (Hemiptera: Psylloidea) species, a psyllid we recently found its distribution in Turkey, for the first time within this study. 
 Material and methods: We collected adults and nymphs of the insect from the host plants during the visits to the study area on different dates. The insect was recognised as a psyllid species. Some adult samples were sent to the expert Dr. Burckhard for species identification. The psyllid damage on host plants of Buxus balearica was identified for the first time as a new host for Spanioneura fonscolombii. 
 Main results: 1- We identified Spaineura fonscolombii species distribution in Turkey for the first time, 2- Population size was highly dense in the study area based on initial observation, 3- New host plant, Buxus balearica, for the pest species was identified for the first time, 4- Overwintering properties of the pest species was determined. 
 Research highlihts: First record of the pest in Turkey. Determination of the most Southern and Eastern, probably so far known, distribution of the pest species in the world. Determination of a new host plant for the pest.

First Report of the Association of the Psyllid Vector Bactericera trigonica (Hemiptera: Triozidae) with 'Candidatus Liberibacter Solanacearum' in Italy.

Psyllids, members of the family Triozidae, represent a potential threat to the cultivation of solanaceous and apiaceous crops worldwide, mainly as vectors of the phloem-restricted bacterium 'Candidatus Liberibacter solanacearum' (Lso). The Lso haplotypes C, D and E are known to affect apiaceous crops, such as carrot and celery, in several European countries. In Italy, data on the incidence and natural spread of both Lso and psyllids have not been reported so far. In this study, the presence of the vectors was investigated in a main Italian district for carrot production, the "Altopiano del Fucino" area (Central Italy). Both occasional and regular surveys were carried out on a total of five carrot fields and one potato field in 2021 and 2022. Bactericera trigonica (Hodkinson), which is known to efficiently transmit Lso to carrots, was found to be well-established in the area. High levels of population density were recorded in the summer period (more than 100 adult specimens per trap caught every two weeks) and then sharply decreased after the carrot harvest, confirming the strict association of this psyllid species with crop availability. In 2022, 27.5% of the total tested psyllid samples resulted in being positive for Lso haplotypes D and E, the latter being prevalent. This survey revealed, for the first time in Italy, the presence of B. trigonica adults associated with Lso in carrot crops. Although this study was limited to a few fields located in one area, it provided important evidence of the risks for Lso outbreaks and prompted further research to assess the spread and incidence of the disease in apiaceous cultivations in Italy.

Wing buzzing as a mechanism for generating vibrational signals in psyllids (Hemiptera: Psylloidea).

Psyllids, or jumping plant lice (Hemiptera: Sternorrhyncha: Psylloidea), are a group of small phytophagous insects that include some important pests of crops worldwide. Sexual communication of psyllids occurs via vibrations transmitted through host plants, which play an important role in mate recognition and localization. The signals are species-specific and can be used to aid in psyllid taxonomy and pest control. Several hypotheses have been proposed for the mechanism that generates these vibrations, of which stridulation, that is, friction between parts of the forewing and thorax, has received the most attention. We have investigated vibrational communication in the European pear psyllid species Cacopsylla pyrisuga (Foerster, 1848) using laser vibrometry and high-speed video recording, to directly observe the movements associated with signal production. We describe for the first time the basic characteristics of the signals and signal emission of this species. Based on observations and analysis of the video recordings using a point-tracking algorithm, and their comparison with laser vibrometer recordings, we argue that males of C. pyrisuga produce the vibrations primarily by wing buzzing, that is, tremulation that does not involve friction between the wings and thorax. Comparing observed signal properties with previously published data, we predict that wing buzzing is the main mechanism of signal production in all vibrating psyllids.

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.

Evaluation of a push-and-pull strategy using volatiles of host and non-host plants for the management of pear psyllids in organic farming.

Pear decline (PD) is one of the most devastating diseases of Pyrus communis in Europe and North America. It is caused by the pathogen 'Candidatus Phytoplasma pyri' and transmitted by pear psyllids (Cacopsylla pyri, C. pyricola, and C. pyrisuga). Identifying attractant and repellent volatile organic compounds (VOCs) could improve the development of alternative plant protection measurements like push-pull or attract-and-kill strategies against pear psyllids. Our objective was to investigate which chemical cues of the host plant could influence the host-seeking behavior of pear psyllids, and if cedarwood (CWO) and cinnamon bark (CBO) essential oils could serve as repellents. Based on the literature, the five most abundant VOCs from pear plants elicited EAG responses in both C. pyri and C. pyrisuga psyllid species. In Y-olfactometer trials, single compounds were not attractive to C. pyri. However, the main compound mixture was attractive to C. pyri and C. pyrisuga females. CWO and CBO were repellent against C. pyri, and when formulated into nanofibers (NF), both were repellent in olfactometer trials. However, CBO nanoformulation was ineffective in masking the odors of pear plants. In a field trial, attractive, repellent CWO and blank formulated NF were inserted in attractive green sticky traps. C. pyri captures in traps with CWO NF were statistically lower than in traps with the attractive mixture. Nevertheless, no statistical differences in the numbers of caught specimens were observed between CWO NF and those captured in green traps baited with blank NF. Transparent traps captured fewer psyllids than green ones. In a second field study with a completed different design (push-and-count design), dispensers filled with CBO were distributed within the plantation, and attractive green sticky traps were placed around the plantation. The numbers of trapped pear psyllids increased significantly in the border of the treated plantation, showing that psyllids were repelled by the EOs in the plantation. Although further field evaluation is needed to assess and improve their effectiveness, our results show that these aromatic compounds, repellent or attractive both in nanoformulations and marking pen dispensers, offer great potential as an environmentally sustainable alternative to currently applied methods for managing pear decline vectors.

Bacterial communities of the psyllid pest Bactericera cockerelli (Hemiptera: Triozidae) Central haplotype of tomato crops cultivated at different locations of Mexico.

The psyllid, Bactericera cockerelli, is an insect vector of 'Candidatus Liberibacter' causing "Zebra chip" disease that affects potato and other Solanaceae crops worldwide. In the present study, we analyzed the bacterial communities associated with the insect vector Bactericera cockerelli central haplotype of tomato crop fields in four regions from Mexico. PCR was used to amplify the mitochondrial cytochrome oxidase I gene (mtCOI) and then analyze the single nucleotide polymorphisms (SNP) and phylogenetic analysis for haplotype identification of the isolated B. cockerelli. Moreover, we carried out the microbial diversity analysis of several B. cockerelli collected from four regions of Mexico through the NGS sequencing of 16S rRNA V3 region. Finally, Wolbachia was detected by the wsp gene PCR amplification, which is the B. cockerelli facultative symbiont. Also we were able to confirm the relationship with several Wolbachia strains by phylogenetic analysis. Our results pointed that B. cockerelli collected in the four locations from Mexico (Central Mexico: Queretaro, and Northern Mexico: Sinaloa, Coahuila, and Nuevo Leon) were identified, such as the central haplotype. Analyses of the parameters of the composition, relative abundance, and diversity (Shannon index: 1.328 ± 0.472; Simpson index 0.582 ± 0.167), showing a notably relatively few microbial species in B. cockerelli. Analyses identified various facultative symbionts, particularly the Wolbachia (Rickettsiales: Anaplasmataceae) with a relative abundance higher. In contrast, the genera of Sodalis and 'Candidatus Carsonella' (Gammaproteobacteria: Oceanospirillales: Halomonadaceae) were identified with a relatively low abundance. On the other hand, the relative abundance for the genus 'Candidatus Liberibacter' was higher only for some of the locations analyzed. PCR amplification of a fragment of the gene encoding a surface protein (wsp) of Wolbachia and phylogenetic analysis corroborated the presence of this bacterium in the central haplotype. Beta-diversity analysis revealed that the presence of the genus 'Candidatus Liberibacter' influences the microbiota structure of this psyllid species. Our data support that the members with the highest representation in microbial community of B. cockerelli central haplotype, comprise their obligate symbiont, Carsonella, and facultative symbionts. We also found evidence that among the factors analyzed, the presence of the plant pathogen affects the structure and composition of the bacterial community associated with B. cockerelli.

Characterizing Substrate-Borne Vibrational Mating Signals Produced by Pear Psylla, Cacopsylla pyricola (Hemiptera: Psyllidae)

AbstractTactics that manipulate insect behavior are a component of many pest management strategies. Pheromone-based mating disruption is one such tactic widely used in agricultural systems, but few studies have assessed disrupting other mate communication mechanisms, such as acoustic signals. The most destructive pear pest in the Pacific Northwest USA, pear psylla (Cacopsylla pyricola) is believed to use acoustic signals to find mates, making it a candidate for this type of disruption. This species has two adult morphs, overwintering adults (winterforms) that emerge in the spring and subsequent generations (summerforms). Our study characterized the mating signals for both sexes and morphs of pear psylla, and assessed whether temperature and previous exposure to adult conspecifics altered signals and likelihood of signaling. While there are descriptions for acoustic signals of other psyllid species, this study provides the first evidence that C. pyricola communicates acoustically. The two sexes communicate via duetting; males signal to attract a female and the female signals back if she is receptive for mating. We showed that both morphotypes’ male signals contain a group of chirps followed by a trill, while females respond with chirps. Male signal trills differed significantly in frequency (Hz) between winterform and summerform psylla. The signal frequency among morphs also had a positive linear relationship with temperature, suggesting that dissimilarity in signals among morphs had some relationship to temperature. Males were more likely to signal when they had previous exposure to females compared to males without exposure to females. Our results provide new information on how pear psylla communicate acoustically for mating, advancing the potential to develop mating disruption strategies for integrated pest management (IPM).

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.

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

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.

The Hidden Secrets of Psylloidea: Biology, Behavior, Symbionts, and Ecology.

Psyllids constitute a diverse group of sap-feeding Sternorrhyncha that were relatively obscure until it was discovered that a handful of species transmit bacterial plant pathogens. Yet the superfamily Psylloidea is much richer than the sum of its crop-associated vectors, with over 4,000 described species exhibiting diverse life histories and host exploitation strategies. A growing body of research is uncovering fascinating insights into psyllid evolution, biology, behavior, and species interactions. This work has revealed commonalities and differences with better-studied Sternorrhyncha, as well as unique evolutionary patterns of lineage divergence and host use. We are also learning how psyllid evolution and foraging ecology underlie life history traits and the roles of psyllids in communities. At finer scales, we are untangling the web of symbionts across the psyllid family tree, linking symbiont and psyllid lineages, and revealing mechanisms underlying reciprocal exchange between symbiont and host. In this review, we synthesize and summarize key advances within these areas with a focus on free-living (nongalling) Psylloidea.

Unveiling metabolic integration in psyllids and their nutritional endosymbionts through comparative transcriptomics analysis

Psyllids, a group of insects that feed on plant sap, have a symbiotic relationship with an endosymbiont called Carsonella. Carsonella synthesizes essential amino acids and vitamins for its psyllid host, but lacks certain genes required for this process, suggesting a compensatory role of psyllid host genes. To investigate this, gene expression was compared between two psyllid species, Bactericera cockerelli and Diaphorina citri, in specialized cells where Carsonella resides (bacteriomes). Collaborative psyllid genes, including horizontally transferred genes, showed patterns of conserved gene expression; however, species-specific patterns were also observed, suggesting differences in the nutritional metabolism between psyllid species. Also, the recycling of nitrogen in bacteriomes may primarily rely on glutamate dehydrogenase (GDH). Additionally, lineage-specific gene clusters were differentially expressed in B.cockerelli and D.citri bacteriomes and are highlighted here. These findings shed light on potential host adaptations for the regulation of this symbiosis due to host, microbiome, and environmental differences.

A 'Candidatus Liberibacter solanacearum' Haplotype B-Specific Family of Candidate Bacterial Effectors.

'Candidatus Liberibacter solanacearum' (Lso) is a phloem-limited pathogen associated with devastating diseases in members of the Solanaceae and Apiaceae and vectored by several psyllid species. Different Lso haplotypes have been identified, and LsoA and LsoB are responsible for diseases in Solanaceae crops. Our efforts are aimed at identifying pathogenicity factors used by this bacterium to thrive in different hosts. Bacterial secreted proteins can play a role in host colonization or the manipulation of the host immune responses; these proteins are called effectors. In this study, we identified six LsoB-specific proteins with a conserved secretion motif as well as a conserved N-terminal domain in the mature protein. These proteins had different expression and secretion patterns but a similar subcellular localization in Nicotiana benthamiana leaves, suggesting that they play different roles regardless of their conserved secretion motif. One of these proteins, CKC_04425, was expressed at high levels in the insect vector and the host plant, indicating that it could play a role in both the plant and insect hosts, whereas the others were mainly expressed in the plant. One protein, CKC_05701, was able to efficiently suppress programmed cell death and reactive oxygen species production, suggesting that it may have a virulence role in LsoB-specific pathogenesis.

Non-destructive insect metabarcoding for surveillance and biosecurity in citrus orchards: recording the good, the bad and the psyllids.

The Australian citrus industry remains one of the few in the world to be unaffected by the African and the Asian citrus psyllids, Trioza erytreae Del Guercio and Diaphorina citri Kuwayama, respectively, and the diseases their vectored bacteria can cause. Surveillance, early detection, and strict quarantine measures are therefore fundamental to safeguard Australian citrus. However, long-term targeted surveillance for exotic citrus pests can be a time-consuming and expensive activity, often relying on manually screening large numbers of trap samples and morphological identification of specimens, which requires a high level of taxonomic knowledge. Here we evaluated the use of non-destructive insect metabarcoding for exotic pest surveillance in citrus orchards. We conducted an 11-week field trial, between the months of December and February, at a horticultural research farm (SuniTAFE Smart Farm) in the Northwest of Victoria, Australia, and processed more than 250 samples collected from three types of invertebrate traps across four sites. The whole-community metabarcoding data enabled comparisons between different trapping methods, demonstrated the spatial variation of insect diversity across the same orchard, and highlighted how comprehensive assessment of insect biodiversity requires use of multiple complimentary trapping methods. In addition to revealing the diversity of native psyllid species in citrus orchards, the non-targeted metabarcoding approach identified a diversity of other pest and beneficial insects and arachnids within the trap bycatch, and recorded the presence of the triozid Casuarinicola cf warrigalensis for the first time in Victoria. Ultimately, this work highlights how a non-targeted surveillance approach for insect monitoring coupled with non-destructive DNA metabarcoding can provide accurate and high-throughput species identification for biosecurity and biodiversity monitoring.

An Overview of the Emergence of Plant Pathogen 'Candidatus Liberibacter solanacearum' in Europe.

In this paper, a comprehensive overview of the 'Candidatus Liberibacter solanacearum' presence in Europe was provided. The analyzed findings revealed that, since the first appearance of this pathogen in Finland and Spain in 2008, it has spread to 13 new European countries. Therefore, 'Ca. L. solanacearum' has spread very quickly across the European continent, as evident from the emergence of new host plants within the Apiaceae, Urticaceae, and Polygonaceae families, as well as new haplotypes of this pathogen. Thus far, 5 of the 15 'Ca. L. solanacearum' haplotypes determined across the globe have been confirmed in Europe (haplotypes C, D, E, U, and H). Fully competent 'Ca. L. solanacearum' vectors include Bactericera cockerelli, Trioza apicalis, and B. trigonica; however, only T. apicalis and B. trigonica are presently established in Europe and are very important for plants from the Apiaceae family in particular. Moreover, psyllid species such as B. tremblayi, T. urticae, and T. anthrisci have also been confirmed positive for 'Ca. L. solanacearum'. Constant monitoring of its spread in the field (in both symptomatic and asymptomatic plants), use of sensitive molecular diagnostic techniques, and application of timely management strategies are, therefore, of utmost importance for the control of this destructive pathogen.

Infection patterns of ‘Candidatus Liberibacter europaeus’ in Cacopsylla oluanpiensis, a psyllid pest of Pittosporum pentandrum

‘Candidatus Liberibacter’ is a genus of plant-associated bacteria that can be transmitted by insects of the superfamily Psylloidea. Since many members of this genus are putative causal agents of plant diseases, it is crucial in studying their interactions with the psyllid vectors. However, previous studies have mainly focused on few species associated with diseases of economic significance, and this may potentially hinder the development of a more comprehensive understanding of the ecology of ‘Ca. Liberibacter’. The present study showed that an endemic psyllid species in Taiwan, Cacopsylla oluanpiensis, is infected with a species of ‘Ca. Liberibacter’. The bacterium was present in geographically distant populations of the psyllid and was identified as ‘Ca. Liberibacter europaeus’ (CLeu), a species which generally does not induce plant symptoms. Analysis of CLeu infection densities in male and female C. oluanpiensis with different abdominal colors using quantitative polymerase chain reaction revealed that CLeu infection was not significantly associated with psyllid gender and body color. Instead, CLeu infection had a negative effect on the body sizes of both male and female psyllids, which is influenced by bacterial titer. Investigation on CLeu’s distribution patterns in C. oluanpiensis’s host plant Pittosporum pentandrum indicated that CLeu does not behave as a plant pathogen. Also, results showed that nymph-infested twigs had a greater chance of carrying high loads of CLeu, suggesting that ovipositing females and the nymphs are the main source of the bacterium in the plants. This study is not only the first to formally report the presence of CLeu in C. oluanpiensis and plants in the family Pittosporaceae, but also represents the first record of the bacterium in Taiwan. Overall, the findings in this work broaden the understanding of associations between psyllids and ‘Ca. Liberibacter’ in the field.