Distribution of Candidatus Liberibacter species in Eastern Africa, and the First Report of Candidatus Liberibacter asiaticus in Kenya

The Combination of Citrus Rootstock and Scion Cultivar Influences Trioza erytreae (Hemiptera: Triozidae) Survival, Preference Choice and Oviposition

Trioza erytreae (Del Guercio, 1918) (Hemiptera: Triozidae) is a citrus pest which produces gall symptoms on leaves and transmits bacteria associated with the citrus disease Huanglongbing, 'Candidatus Liberibacter' spp. In the present work, the biology and behaviour of T. erytreae were studied in different rootstock-cultivar combinations. Six rootstocks were used, Flying dragon (FD), 'Cleopatra' mandarin (CL), Carrizo citrange (CC), Forner-Alcaide no.5 (FA5), Forner-Alcaide no.517 (FA517) and Citrus macrophylla (CM), and six scion cultivars: 'Star Ruby', 'Clemenules', 'Navelina', 'Valencia Late', 'Fino 49' and 'Ortanique'. Survival and oviposition were evaluated in a no-choice trial, and preference in a choice trial, all of them under greenhouse conditions. Trioza erytreae did not show a clear settle preference for any citrus combination. However, it was able to lay more eggs in 'Fino 49' grafted on CC than on FD. In terms of survival, 'Ortanique' grafted onto FA5 was more suitable than when grafted onto FA517, and in the case of 'Valencia Late', when it was grafted onto CM rather than CC. Our results showed that T. erytreae behave differently depending on the citrus combination.

Identification and Distribution of the 'Candidatus Liberibacter asiaticus'-Asian Citrus Psyllid Pathosystem in Saudi Arabia

Citrus greening disease was first reported in Saudi Arabia during the 1970s when characteristic foliar and fruit symptoms were observed in commercial citrus groves. However, 'Candidatus Liberibacter asiaticus' (CLas) was not detected in symptomatic trees until 1981 to 1984 when CLas-like cells were observed by transmission electron microscopy in leaves collected from symptomatic citrus groves in southwestern Saudi Arabia. Despite the anticipated establishment of the CLas-Asian citrus psyllid (ACP) (Diaphorina citri Kuwayama) pathosystem, CLas presence has not been verified in suspect trees nor have ACP infestations been documented. Given the recent expansion of citrus production in Saudi Arabia, a systematic country-wide survey was carried out to determine the potential CLas distribution in the 13 citrus-growing regions of the country. Citrus trees were surveyed for the presence of CLas-psyllid vector(s) and characteristic disease symptoms in commercial and urban citrus trees. Adult psyllids collected from infested citrus trees were identified as ACP based on morphological characteristics. Real-time quantitative PCR amplification (qPCR) of the CLas β-subunit of the ribonucleotide reductase (RNR) gene from citrus leaf and fruit samples and/or ACP adults revealed that trees were positive for CLas detection in 10 of the 13 survey regions; however, CLas was undetectable in ACP adults. Phylogenetic and single nucleotide polymorphism (SNP) analyses of a PCR-amplified, cloned fragment of the CLas 16S rRNA gene (∼1.1 kbp) indicated Saudi Arabian isolates were most closely related to Florida, U.S.A., isolates. Analysis of climate variables indicated that the distribution of the ACP-CLas pathosystem observed in Saudi Arabia was consistent with published predictions of terrains most likely to support establishment.

The African Psyllid Trioza erytreae Del Guercio (1918) Is Very Sensitive to Low Relative Humidity and High Temperatures

The African citrus psyllid, Trioza erytreae, is one of the two vectors of Huanglongbing, the most serious citrus disease worldwide. The first detection of T. erytreae in the European mainland was on the northwest of the Iberian Peninsula in 2014. Since then, the pest has spread throughout northern Spain (Galicia, Asturias, Cantabria, País Vasco) and along the western Atlantic coast of Portugal (from the Douro e Minho region to the Algarve). We conducted a series of laboratory experiments on lemon plants at different temperatures (from 8 to 34 °C) and humidity conditions (from 40 to 90%) to find out the influence of extreme temperatures and relative humidities (RHs) on the mortality, development and reproduction of T. erytreae. Our results show that temperatures above 30 °C and below 10 °C are very detrimental for nymphal development and nymphs were unable to reach the adult stage. Furthermore, eggs were unable to hatch under temperatures above 33 °C and below 8 °C. Adult mortality was highest at 34 °C and killed more than 50% of the population. We also found that relative humidity is crucial for the development and survival of T. erytreae. Nymphs were unable to reach the adult stage at an RH of 90% and 40%. Also, fecundity was significantly reduced at 90 and 40% RH, and fertility was lowest at 40% RH. Nymphal mortality was highest at an RH of 40%, which was the most detrimental humidity among all tested for the survival and development of T. erytreae. Our work concludes that T. erytreae establishment and spread will be maximum in regions with a temperate and humid climate, being rare in regions where dry and hot weather conditions predominate.

Population dynamics and insecticide resistance in Tuta absoluta (Lepidoptera: Gelechiidae), an invasive pest on tomato in Kenya

Tuta absoluta feeds on solanaceous plants with preference on tomato. Management of the pest is mostly with chemical insecticides. This study identified insecticide resistant populations and predicted resistance to insecticides. Insecticide resistance development was modelled using system thinking, and system dynamics approaches. The model showed the pest resistance development is alarming with an exponential increase of the resistance strength mostly in recent years. Furthermore, we used seven insecticide-resistance gene markers to resolve the population structure and genetic differentiation of insecticide-resistant populations in Kenya. The genes for resistance (knockdown resistance (kdr) mutations, acetylcholinesterase (AChE) and voltage gated sodium channel (para)) were detected in all populations. Population structure analyses separated T. absoluta populations into three genetic clusters with resistant genes that are interconnected. A better insight on the population dynamics and the genetic structure T. absoluta resistant genes in Kenya will help estimate resistance strength and determine the most effective pest control strategies.

Modelling the spread and mitigation of an emerging vector-borne pathogen: Citrus greening in the U.S

Predictive models, based upon epidemiological principles and fitted to surveillance data, play an increasingly important role in shaping regulatory and operational policies for emerging outbreaks. Data for parameterising these strategically important models are often scarce when rapid actions are required to change the course of an epidemic invading a new region. We introduce and test a flexible epidemiological framework for landscape-scale disease management of an emerging vector-borne pathogen for use with endemic and invading vector populations. We use the framework to analyse and predict the spread of Huanglongbing disease or citrus greening in the U.S. We estimate epidemiological parameters using survey data from one region (Texas) and show how to transfer and test parameters to construct predictive spatio-temporal models for another region (California). The models are used to screen effective coordinated and reactive management strategies for different regions.

The African citrus psyllid Trioza erytreae: An efficient vector of Candidatus Liberibacter asiaticus

INTRODUCTION

Huanglonbing (HLB) is the most serious disease of citrus in the world, associated with three non-cultivable phloem-restricted bacteria Candidatus Liberibacter asiaticus (CLas), Ca L. africanus (CLaf) and Ca L. americanus (CLam). CLas is transmitted by the Asian citrus psyllid Diaphorina citri, and has spread to several countries. The African psyllid Trioza erytreae, the vector of CLaf occurs in Africa and neighbouring islands. Only two major citrus-growing regions - Australia/New Zealand and the Mediterranean Basin - are still HLB-free in the world. However, T. erytreae has recently been introduced into continental Europe (Portugal and Spain) and has become a potential threat to citrus production. The transmission of CLas by T. erytreae had been postulated but never tested. To evaluate the risk of T. erytreae transmitting CLas, comparative transmissions of CLas by T. erytreae and D. citri were assessed.

METHODS

Transmission tests were performed on excised leaves and seedlings of Citrus volkameriana with different inoculation access periods (in series) for both insect species. Quantifications of bacterial titers were made in excised leaves, seedlings three and six months after inoculation and on individual insects.

RESULTS

Our results showed that T. erytreae was able to efficiently acquire CLas. Furthermore, T. erytreae carried significantly higher bacterial titers than D. citri, and was able to efficiently transmit the bacteria to seedlings at a similar rate that D. citri highlighting the high risk of spread of the most aggressive variant of HLB (CLas) by T. erytreae in Europe.

DISCUSSION

Thus, extreme precautions to prevent any entry of CLas into Europe should be adopted.

Genetic Diversity of "Candidatus Liberibacter asiaticus" Based on Four Hypervariable Genomic Regions in China

Huanglongbing (HLB; greening disease), caused by Candidatus Liberibacter asiaticus (CLas), is the most damaging citrus disease worldwide. The disease has spread throughout the citrus-producing regions of Guangxi, Guangdong, Fujian, and others in China. A total of 1,788 HLB-like symptomatic or asymptomatic samples were collected from the Guangxi and Fujian provinces of China to decipher the genetic diversity of CLas and its correlation with geographic region and host plant. The disease was the most severe in orange and the least in pomelo. CLas bacteria associated with the specific geographical and citrus variety infected more than 50% of the HLB-like symptomatic samples. We identified 6,286 minor variations by comparing 35 published CLas genomes and observed a highly heterogeneous variation distribution across the genome, including four highly diverse nonprophages and three prophage segments. Four hypervariable genomic regions (HGRs) were identified to determine the genetic diversity among the CLas isolates collected from Guangxi and Fujian, China. A phylogenetic tree constructed from four HGRs showed that 100 CLas strains could be separated into four distinct clades. Ten new strains with high variations of prophage regions were identified in the mandarin and tangerine grown in new plantation areas of Guangxi. Characterizing these HGR variations in the CLas bacteria may provide insight into their evolution and adaptation to host plants and insects. IMPORTANCE The hypervariable genomic regions derived from 35 published CLas genomes were used to decipher the genetic diversity of CLas strains and identify 10 new strains with high variations in prophage regions. Characterizing these variations in the CLas bacteria might provide insight into their evolution and adaptation to host plants and insects in China.

Integrated Pest Management Strategies for Asian Citrus Psyllid Diaphorina citri Kuwayama (Hemiptera: Psyllidae) and Huanglongbing in Citrus for Sarawak, East Malaysia, Borneo

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, transmits ‘Candidatus Liberibacter asiaticus’ (CLas), a phloem-limited bacterium associated with the severe Asian form of huanglongbing (HLB), and the most destructive disease of citrus. The pathogen and the psyllid, both of South Asian origin, are now widespread in citrus regions of Asia and the Americas. There is no cure for the disease. Application of synthetic pesticides, in some instances more frequently than fortnightly, to minimise incidence of ACP in citrus orchards, has not prevented inevitable impacts of the disease in regions of Asia where CLas is present. Despite the inevitable spread of the disease, significant progress has been made in Sarawak since the mid-1990s towards effectively implementing integrated pest management (IPM) programs for stemming the impact of the disease and detrimental consequences of over-reliance on synthetic pesticides. Growers are encouraged to plant pathogen-free trees, remove diseased trees, monitor incidence of the psyllid, and to use pesticides judiciously to reduce their detrimental impacts on natural enemies. Knowledge has been enhanced through research on seasonal incidence of the psyllid, use of mineral oils, development of protocols and iodine−starch test kits for detecting infected trees, PCR for confirming the presence of CLas in symptomatic leaves, methods for monitoring incidence the psyllid, and training extension staff and growers. However, major impediments to increasing the average longevity of trees beyond <5 years in poorly managed orchards, based on marcotting (air layering), and >12 years in well-managed orchards, based on pathogen-free trees, still need to be addressed. These include grower knowledge, marcotting, aggressive marketing of synthetic pesticides, high prices of mineral oils, spray application procedures, and better reliance on natural enemies of the psyllid.

Genetic diversity of Diaphorina citri (Hemiptera: Liviidae) unravels phylogeographic structure and invasion history of eastern African populations

The Asian citrus psyllid (Diaphorina citri Kuwayama) is a key pest of Citrus sp. worldwide, as it acts as a vector for Candidatus Liberibacter asiaticus, the bacterial pathogen that causes citrus Huanglongbing. Diaphorina citri has been reported in Kenya, Tanzania, and more recently in Ethiopia. This study assessed the genetic diversity and phylogeographic structure of the pest to gain insights into the potential sources of its introduction into Africa. Population structure and differentiation of D. citri populations from China, Ethiopia, Kenya, Tanzania, and the USA were assessed using 10 microsatellite loci. Additionally, five new complete mitogenomes of D. citri collected in China, Ethiopia, Kenya, Tanzania, and the USA were analyzed in the context of publicly available sequences. Genotype data grouped the D. citri populations from Kenya and Tanzania in one cluster, and those from Ethiopia formed a separate cluster. The two genetic clusters inferred from genotype data were congruent with mitochondrial sequence data. The mitogenomes from Kenya/Tanzania/China had 99.0% similarity, and the Ethiopia/USA had 99.9% similarity. In conclusion, D. citri populations in eastern Africa have different sources, as the Kenyan and Tanzanian populations probably originated from southeastern Asia, while the Ethiopian population most probably originated from the Americas.

Cultural Management of Huanglongbing: Current Status and Ongoing Research

Huanglongbing (HLB), formerly known as greening, is a bacterial disease restricted to some Asian and African regions until two decades ago. Nowadays, associated bacteria and their vectors have spread to almost all citrus-producing regions, and it is currently considered the most devastating citrus disease. HLB management can be approached in terms of prevention, limiting or avoiding pathogen and associated vectors to reach an area, or in terms of control, trying to reduce the impact of the disease by adopting different cultural strategies depending on infestation/infection levels. In both cases, control of psyllid populations is currently the best way to stop HLB spread. Best cultural actions (CHMAs, TPS system) to attain this goal and, thus, able to limit HLB spread, and ongoing research in this regard is summarized in this review.

A Review of the 'Candidatus Liberibacter africanus' Citrus Pathosystem in Africa

It has been nearly 100 years since citrus growers in two distinct regions in the northern provinces of South Africa noticed unusual symptoms in their citrus trees, causing significant crop losses. They had no idea that these symptoms would later become part of an almost global pandemic of a disease called greening or huanglongbing (HLB). The rapid spread of the disease indicated that it might be caused by a transmissible pathogen, but it took >50 years to identify the causative agent as 'Candidatus Liberibacter africanus'. Recently, the disease appeared in more African countries, spreading by both infected planting material and Trioza erytreae. To date, five 'Ca. L. africanus' subspecies have been identified in various rutaceous species, with 'Ca. L. africanus subsp. clausenae' the only subspecies for which a biovar was detected in citrus. Efforts to detect and differentiate HLB-causing Liberibacter species are ongoing, and recent developments are discussed here. This review focuses on aspects of the African form of HLB, including its specific bacterial species and subspecies, its main insect vector, its geographic distribution, and current management strategies.

Photodynamic control of citrus crop diseases

Citrus are economically important fruit crops to which infectious diseases like citrus canker caused by Xanthomonas citri subs. citri, citrus variegated chlorosis caused by Xylella fastidiosa, "huanglongbing" associated with the presence of Candidatus liberibacter species, anthracnose caused by Colletotrichum gloeosporioides and citrus black spot caused by Phyllosticta citricarpa, impose significant losses. Control measures involve chemical treatment of orchards but often, eradication of infected plants is unavoidable. To circumvent the environmental impacts of pesticides and the socio-economic impacts of eradication, innovative antimicrobial approaches like photodynamic inactivation are being tested. There is evidence of the susceptibility of Xanthomonas citri subs. citri and C. gloeosporioides to photodynamic damage. However, the realistic assessment of perspectives for widespread application of photodynamic inactivation in the control of citrus diseases, necessarily implies that other microorganisms are also considered. This review intends to provide a critical summary of the current state of research on photodynamic inactivation of citrus pathogens and to identify some of the current limitations to the widespread use of photodynamic treatments in citrus crops.

The molecular interplay of the establishment of an infection - gene expression of Diaphorina citri gut and Candidatus Liberibacter asiaticus

BACKGROUND

Candidatus Liberibacter asiaticus (CLas) is one the causative agents of greening disease in citrus, an unccurable, devastating disease of citrus worldwide. CLas is vectored by Diaphorina citri, and the understanding of the molecular interplay between vector and pathogen will provide additional basis for the development and implementation of successful management strategies. We focused in the molecular interplay occurring in the gut of the vector, a major barrier for CLas invasion and colonization.

RESULTS

We investigated the differential expression of vector and CLas genes by analyzing a de novo reference metatranscriptome of the gut of adult psyllids fed of CLas-infected and healthy citrus plants for 1-2, 3-4 and 5-6 days. CLas regulates the immune response of the vector affecting the production of reactive species of oxygen and nitrogen, and the production of antimicrobial peptides. Moreover, CLas overexpressed peroxiredoxin, probably in a protective manner. The major transcript involved in immune expression was related to melanization, a CLIP-domain serine protease we believe participates in the wounding of epithelial cells damaged during infection, which is supported by the down-regulation of pangolin. We also detected that CLas modulates the gut peristalsis of psyllids through the down-regulation of titin, reducing the elimination of CLas with faeces. The up-regulation of the neuromodulator arylalkylamine N-acetyltransferase implies CLas also interferes with the double brain-gut communication circuitry of the vector. CLas colonizes the gut by expressing two Type IVb pilin flp genes and several chaperones that can also function as adhesins. We hypothesized biofilm formation occurs by the expression of the cold shock protein of CLas.

CONCLUSIONS

The thorough detailed analysis of the transcritome of Ca. L. asiaticus and of D. citri at different time points of their interaction in the gut tissues of the host led to the identification of several host genes targeted for regulation by L. asiaticus, but also bacterial genes coding for potential effector proteins. The identified targets and effector proteins are potential targets for the development of new management strategies directed to interfere with the successful utilization of the psyllid vector by this pathogen.

In situ diagnosis of mature HLB-asymptomatic citrus fruits by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a promising alternative to conventional methods in classifying citrus huanglongbing (HLB). Mature citrus fruits with similar features were picked and divided into healthy and HLB-asymptomatic groups. LIBS spectra and images were collected by focusing a laser on fresh fruit surfaces without sample preparation. The pH value and soluble solids content of juice as the indicators of acidity and sugar were detected, and the content of Ca, Zn, and K in peel and pulp was analyzed. The characteristic lines from LIBS spectra were extracted by continuous wavelet transform and principal component analysis (PCA). The t-test of these indicators displayed significant difference between the two groups. Fisher discriminant analysis and multilayer perception neural network (MLP) were applied to identify the disease. The classification accuracy reached 100% by PCA-MLP. The results show that LIBS can realize in situ detection of citrus HLB fruits.

Does the African Citrus psyllid, Trioza erytreae (Del Guercio) (Hemiptera: Triozidae), Represent a Phytosanitary Threat to the Citrus Industry in Mexico?

Simple Summary

The African citrus psyllid, Trioza erytreae (Del Guercio) (Hemiptera: Triozidae) is an invasive species for citrus crops. In its native range is the main vector of Candidatus Liberibacter africanus (CLaf), a pathogen that causes huanglongbing (HLB). For Mexico, T. erytreae could threat the citrus industry in a potential invasion but until now, the best chances to prevent its damage is analyzing if the country has the ecological conditions suitable for this psyllid. In this study we used the ecological niche modeling approach to explore which areas in Mexico has the environmental suitability for the T. erytreae establishment. Additionally, the potential role of an alternate host, Casimiroa edulis La Llave (Rutaceae), and five points of entry into the country, in the potential T. erytreae dispersion were analyzed. Mexico citrus areas has a wide environmental suitability for T. erytreae, including the main federal entity (Veracruz). The natural distribution of C. edulis matches with the T. erytreae environmental suitability and citrus areas, and could expand its distribution across the country. For preventive monitoring strategies, the port of Veracruz is a vital point for phytosanitary agencies, because of its proximity to citrus areas.

Abstract

The African citrus psyllid, Trioza erytreae (Del Guercio) (Hemiptera: Triozidae), is a vector of Candidatus Liberibacter africanus (CLaf), a pathogen that causes huanglongbing (HLB) in Africa. Trioza erytreae has invaded areas of Asia and Europe and has threatened citrus production due to its biological habits and the transmission of CLaf. Mexico is a country where citrus production has a vital role from the economic and social point of view. Therefore, ecological niche modeling (ENM) was used to determine if Mexico has the environmental availability that will allow T. erytreae invasion. We analyzed whether or not the distribution of Casimiroa edulis La Llave (Rutaceae) in the country could be a factor that enables the dispersal of T. eytreae. The environmental connectivity between five points of entry into the country (two ports and three airports) was explored to determine possible routes of dispersal of T. erytrae. The results showed that Mexico has wide availability for the invasion of the African citrus psyllid, which coincides with essential citrus areas of the country and with the distribution of C. edulis. Of the entry points studied, the Port of Veracruz showed nearby areas with environmental connectivity. Preventive monitoring measures for T. erytreae in Mexico should focus on Veracruz state because it has an entry point, ideal environmental availability, citrus areas, and specimens of C. edulis.

Genetic diversity and population structure of 'Candidatus Liberibacter asiaticus' associated with citrus Huanglongbing in India based on the prophage types

Huanglongbing (HLB), also known as 'citrus greening', is an extremely destructive disease of citrus worldwide. HLB is associated with three species of the fastidious proteobacterium, Candidatus Liberibacter asiaticus (CaLas), Ca. L. africanus and Ca. L. americanus with CaLas being the most widely distributed around the world and the only species detected and described so far in India, one of the major global citrus fruit producers. Prophages are highly dynamic components in the bacterial genome and play an important role in intraspecies variations. Three types of prophages, Type 1, Type 2 and Type 3 have been identified and described in CaLas so far. In the present study, 441 CaLas isolates sampled across 18 Indian states were used for prophage typing. Based on detection of three prophage types by PCR, all the eight probable combinations of CaLas prophages were identified, including single Type 1 (26.5%), single Type 2 (18.8%), single Type 3 (1.4%), Type 1 + Type 2 (20.4%), Type 1 + Type 3 (12.5%), Type 2 + Type 3 (4.8%), Type 1 + Type 2 + Type 3 (11.3%) and None type (4.3%). Prophage types were confirmed by PCR amplicon sequencing and subsequent phylogenetic analysis. By discovery of all 3 prophages and based on genetic identity and genetic distance, CaLas populations from eighteen citrus growing states were separated into two major Prophage Typing Groups (PTGs): PTG1 and PTG2. The PTG1 comprised of CaLas from North-West India and PTG2 from rest of the country (North-East, Central and South India), and both major groups were further divided into two (PTG1-A, PTG1-B) and three (PTG2-A, PTG2-B and PTG2-C) subgroups respectively. The findings of CaLas population patterns provide evidence for independent origins of HLB-associated CaLas. CRISPR (clustered regularly interspaced short palindromic repeats) array was also detected in CaLas isolates. This is the first report evaluating the genetic variation of a large population of CaLas bacterium in India using the PCR markers from the prophage regions which would certainly assist the ongoing HLB management efforts in India.

Genome Sequence Resource of 'Candidatus Liberibacter asiaticus' from Diaphorina citri Kuwayama (Hemiptera: Liviidae) from La Réunion

'Candidatus Liberibacter asiaticus' is an insect-transmitted, phloem-restricted α-proteobacterium associated with huanglongbing. Here, we provide the whole genome sequence of 'Ca. L. asiaticus' strain ReuSP1 from its insect vector Diaphorina citri (Hemiptera: Liviidae) collected in La Réunion. The genome is composed of 1,230,064 bp and has a 36.5% G+C content. This study reports the first 'Ca. L. asiaticus' genome sequence from La Réunion, which will add to 'Ca. L. asiaticus' genome resources and help elucidate our understanding of the introduction pathway into La Réunion.

Pest categorisation of Diaphorina citri

The EFSA Panel on Plant Health performed a pest categorisation of Diaphorina citri (Hemiptera: Liviidae) (Asian citrus psyllid) for the EU. D. citri is a key pest of citrus in several countries as it is a vector of serious bacterial pathogens, the putative causal agents of Huanglongbing (HLB) also known as citrus greening. Eggs are laid on tips of growing shoots on and between unfurling leaves. Females may lay more than 800 eggs during their lives. Nymphs pass through five instars. The life cycle requires from 14 to 49 days, depending upon the season. There is no diapause, but populations are low in winter. It overwinters as an adult which may live for several months. The species completes 9-10 generations/year; however, under protected conditions, up to 16 generations have been recorded. Commission Implementing Regulation (EU) 2019/2072 (Annex IIA) regulates D. citri, as a quarantine pest not known to occur in the EU territory. Fruits and plants for planting provide potential pathways for entry into the EU. Climatic conditions and the availability of host plants provide conditions to support establishment in the EU. The introduction of D. citri would have an economic impact in the EU through direct but mainly indirect effects due to potential transmission of HLB. Phytosanitary measures are available to reduce the likelihood of entry. D. citri satisfies the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. D. citri does not meet the criteria of occurring in the EU, nor plants for planting being the principal means of spread, for it to be regarded as a potential Union regulated non-quarantine pest.