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Citrus huanglongbing (HLB) is a destructive disease of citrus and a major threat to the citrus industry around the world. This disease accounts for substantial economic losses in China every year. Kuwayama is one of the major vectors by which citrus HLB is spread under natural conditions in China. Research is needed to identify the geographic distribution of and its major areas of occurrence and to formulate measures for early warning, monitoring, and control of this pest and citrus HLB. In this study, the ecological niche modelling software MaxEnt (maximum entropy model) was combined with ArcGIS (a geographic information system) to predict the potential geographic distribution of in China. Key environmental factors and the appropriate ranges of their values were also investigated. Our results show that the training data provided a good forecast (AUC = 0.988). The highly suitable areas for in China are mainly concentrated to the south of the Yangtze River, and the total area is 139.83 × 10 km . The area of the moderately suitable areas is 27.71 × 10 km , with a narrower distribution than that of the highly suitable area. The important environmental factors affecting the distribution of were min temperature of coldest month, mean temperature of coldest quarter, precipitation of wettest quarter, mean temperature of warmest quarter, precipitation of warmest quarter, max temperature of warmest month, and temperature seasonality. These results provide a valuable theoretical basis for risk assessments and control of . The predicted results showed that there were highly suitable areas for in Chongqing, Hubei, Anhui, and Jiangsu. Therefore, the possibility exists for the further spread of in China in the future. Extreme temperature variables, especially the min temperature of the coldest month, play an important role in the distribution of and are most closely related to the distribution of .

Asian citrus psyllid (Diaphorina citri) transmits the bacterial pathogen Candidatus Liberibacter asiaticus (CLas), the putative causative agent of citrus Huanglongbing disease (HLB). Insect-specific viruses can act against insects as their natural enemies, and recently, several D. citri-associated viruses were discovered. The insect gut plays an important role as not only a pool for diverse microbes but also as a physical barrier to prevent the spread of pathogens such as CLas. However, there is little evidence of the presence of D. citri-associated viruses in the gut and of the interaction between them and CLas. Here, we dissected psyllid guts collected from five growing regions in Florida, and the gut virome was analyzed by high throughput sequencing. Four insect viruses, including D. citri-associated C virus (DcACV), D. citri densovirus (DcDV), D. citri reovirus (DcRV), and D. citri flavi-like virus (DcFLV), were identified, and their presence in the gut, including an additional D. citri cimodo-like virus (DcCLV), were confirmed with PCR-based assays. Microscopic analysis showed that DcFLV infection leads to morphological abnormalities in the nuclear structure in the infected psyllid gut cells. The complex and diverse composition of microbiota in the psyllid gut suggests a possible interaction and dynamics between CLas and the D. citri-associated viruses. Our study identified various D. citri-associated viruses that localized in the psyllid gut and provided more information that helps to evaluate the potential vectors for manipulating CLas in the psyllid gut.

Societal Impact Statement Huánglóngbìng (HLB) is a bacterial disease of citrus that has significantly impacted Brazil and the United States, although citrus production in the Mediterranean Basin remains unaffected. By developing a mathematical model of spread in Spain, we tested surveillance and control strategies before any future HLB entry in the EU. We found while some citrus production might be maintained by roguing, this requires extensive surveillance and significant chemical control, perhaps also including testing of psyllids (which spread the pathogen) for bacterial DNA. Our work highlights the key importance of early detection (including asymptomatic infection) and vector control for HLB management. Summary • Huánglóngbìng (HLB; citrus greening) is the most damaging disease of citrus worldwide. While citrus production in the United States and Brazil have been affected for decades, HLB has not been reported in the European Union (EU). However, a HLB vector, the African citrus psyllid, is already in Portugal and Spain. In 2023, the major vector, the Asian citrus psyllid, was first reported in Cyprus. • We develop a landscape-scale, epidemiological model, accounting for heterogeneous citrus cultivation and vector dispersal, as well as climate and disease management. We use our model to predict HLB dynamics for an epidemic vectored by the African citrus psyllid in high-density citrus areas in Spain, assessing detection and control strategies. • Without disease management, we predict large areas infected within 10–20 years. Even with significant visual surveillance, any epidemic will be widespread on first detection, making eradication unlikely. Nevertheless, increased inspection and roguing following first detection, particularly if coupled with intensive insecticide use, could sustain some citriculture for a decade or more, albeit with reduced production. However, effective control may require chemical application rates and/or active substances no longer authorised in the EU. Strategies targeting asymptomatic infection will be more successful. Detection of bacteriliferous vectors—sometimes possible long before plants show symptoms—could reduce lags before disease management commences. If detection of HLB-positive vectors were followed by intensive insecticide sprays, this may greatly improve outcomes. • Our work highlights modelling as a key component of developing epidemiological preparedness for a pathogen invasion that is, at least somewhat, predictable in advance.

Nowadays, citrus greening or Huanglongbing is considered the most destructive disease in the citrus industry worldwide. In the Americas and Asia, the disease is caused by the putative pathogen, ‘Candidatus Liberibacter asiaticus’ and transmitted by the psyllid vector, Diaphorina citri. It has been shown that volatile organic compounds (VOC) that are released from citrus leaves attract the psyllid vector. Herein, we tested whether the rootstock influenced the stored VOC profile in the scion leaves and if these influences were altered after infestation with D. citri. The VOC profiles of the hexane-extracted leaves of the mandarin hybrid ‘Sugar Belle’ that were grafted on three different rootstocks (C-35, sour orange (SO), and US-897) with and without infestation with D. citri were studied. The GC-MS analysis showed that the scion VOC profiles of the non-infested control trees were similar to each other, and rootstock was not a strong influence. However, after one month of infestation with D. citri, clear differences in the scion VOC profiles appeared that were rootstock dependent. Although the total scion leaf VOC content did not differ between the three rootstocks, the infestation increased scion monoterpenes significantly on US-897 and C-35 rootstock, increased terpene alcohols on US-897 and SO rootstock, and increased sesquiterpenes on SO. Infestation with D. citri significantly reduced fatty acids and fatty acid esters across all of the rootstocks. Therefore, our results suggest that rootstock choice could influence scions with an inducible volatile defense by enhancing the amounts of VOCs that are available for repelling vectors or for signaling to their natural enemies or parasitoids. According to this study, US-897 may be the best choice among the three that were studied herein, due to its diverse and robust VOC defense response to infestation with D. citri.

Nowadays, the Asian citrus psyllid, Diaphorina citri (Kuwayama) (Hemiptera: Liviidae) is considered the most devastating pest of citrus because it transmits “Candidatus Liberibacter asiaticus”, the putative causal agent of huanglongbing (HLB) or citrus greening. Controlling the vector is the main strategy used to mitigate HLB. Targeting D. citri at the very early stages of its development may offer an effective control strategy. Identifying chorion proteins will contribute to a better understanding of embryo development and egg hatching and thus could lead to valuable targets to better control psyllid populations. Herein, we analyze the chorion proteins of D. citri. Mass spectrometry-based bottom-up/shotgun proteomics and databases were queried to achieve protein identification. Fifty-one proteins were identified in D. citri chorion. The D. citri chorion proteins were divided into eight categories according to their biological or molecular function: i—enzymes (25%); ii—binding proteins (10%); iii—structural proteins (8%); iv—homeostasis-related proteins, mostly vitellogenins (8%); v—proteins related to gene expression (6%); vi—immune system proteins (6%); vii—other proteins (16%); and viii—uncharacterized proteins (21%). The composition of the chorion proteome suggested that the hatching rate could be reduced by silencing chorion-related genes. The proteomic analysis of D. citri chorion tissue allowed us to identify its proteins, providing promising new targets for D. citri control through RNA interference technology.

Potential insecticides generated from several plants or some plant wastes are used to control citrus psyllid Diaphorina citri. The aim of the study was to determine the toxicity of botanical insecticides from the extract of tobacco leaf, marigold leaves and Japansche citroen (JC) citrus peel against D. citri. The three plants, which were extracted with five kinds of solvents, namely acetone, distilled water, dichlormethane, hexane and methanol by maceration method. The test used leaf dipping method at 10% concentration with control and imidacloprid chemical insecticide as a comparison. The results showed that tobacco extract with all solvents was effective in controlling D. citri, starting at 1 day after treatment (DAT) with 44-92% mortality. The effective marigold leaf extract was those with the solvent of distilled water, dichlormethane and acetone. The mortality at 8 DAT was 100% and 70% and 74% respectively. Meanwhile, JC citrus peel extract with acetone, methanol and dichlormethane solvents were effective to control D. citri with the mortality at 8 DAT, the mortality reached 98%; 88% and 70% respectively. Thus, botanical insecticides of tobacco, marigold and JC orange peel with certain solvents can be used as controller of D. citri.

The Asian citrus psyllid, Diaphorina citri Kuwayama, was discovered in Florida in 1998. It can be one of the most serious pests of citrus if the pathogens that cause citrus greening disease (huanglongbing) are present. Citrus greening recently has been reported in Brazil by Fundecitrus, Brazil. The establishment of D. citri in Florida increases the possibility that the disease may become established. Diaphorina citri can be separated from about 13 other species of psyllids reported on citrus. The biology of D. citri makes it ideally suited to the Florida climate. Only two species, D. citri and Trioza erytreae (del Guercio), have been implicated in spread of citrus greening, a disease caused by highly fastidious phloem-inhabiting bacteria. The disease is characterized by blotchy mottle on the leaves, and misshapen, poorly colored off-tasting fruit. In areas where the disease is endemic, citrus trees may live for only 5-8 years and never bear usable fruit. The disease occurs throughout much of Asia and Africa south of the Sahara Desert, on several small islands in the Indian Ocean, and in the Saudi Arabian Peninsula. Transmission of citrus greening occurs primarily via infective citrus psyllids and grafting. It is transmissible experimentally through dodder and might be transmitted by seed from infected plants and transovarially in psyllid vectors. Citrus greening disease is restricted to Citrus and close citrus relatives because of the narrow host range of the psyllid vectors. Management of citrus greening disease is difficult and requires an integrated approach including use of clean stock, elimination of inoculum via voluntary and regulatory means, use of pesticides to control psyllid vectors in the citrus crop, and biological control of psyllid vectors in non-crop reservoirs. There is no place in the world where citrus greening disease occurs that it is under completely successful management. Eradication of citrus greening disease may be possible if it is detected early. Research is needed on rapid and robust diagnosis, disease epidemiology, and psyllid vector control.

Huanglongbing (citrus greening) is one of the most serious diseases of citrus. Movement of the disease occurs as a result of natural transmission by the insect vector and by movement of infected plant material. We demonstrate here that Diaphorina citri Kuwayama, the vector of citrus greening pathogens, can be transported in trailers of unprocessed fruit. Several samples of D. citri collected from trailers of oranges were positive for citrus greening pathogens, indicating that the disease can spread widely with the movement of the mature fruit as a result of moving the vectors. While movement of disease and the vector through plant materials into new areas has been recognized, our findings emphasize the need to evaluate the importance of long distance movement of psyllids on unprocessed fruit, even in the absence of vegetative tissue.

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is the vector of the bacterial pathogens that cause Huanglongbing (HLB), considered to be the most devastating disease of citrus worldwide. Knowledge of the ACP’s host-plant finding behavior aids in our understanding of the epidemiology of HLB and in designing experiments to investigate host plant resistance to ACP. We present the results of research conducted to assess the ability of adult ACP to distinguish between a non-host plant [Rhododendron simsii Planch. (Ericales: Ericaceae)] and two host plant species [Murraya paniculata (L.) Jack and “Lugan” Citrus reticulata Blanco (Sapindales: Rutaceae)] in a caged, free-choice situation. After being introduced into cages with the three plant species, more than 9 h elapsed before adult ACP made definite plant choices. Subsequently for more than 7 days, although adults were observed on R. simsii each time the plants were inspected, greater numbers were usually observed on M. paniculata or C. reticulata. Ultimately, most adults were on C. reticulata, intermediate numbers were on M. paniculata, and few were on R. simsii. However, at least some ACP adults were always observed on R. simsii, suggesting that adults regularly moved within a cage among the plant species. Regular movement of adults between plants would favor dissemination not only of its population but also of HLB. Adult ACP showed a strong preference for settling on flush leaves as opposed to mature leaves or other plant locations, and larger flush shoots were as attractive as tiny new shoots. It is well known that host plant volatiles such as those associated with flush attract ACP adults and regulate how fast and where they settle on a plant.

The biology and behaviour of the psyllid Diaphorina citri Kuwayama (Hemiptera: Sternorrhyncha: Liviidae), the major insect vector of bacteria associated with huanglongbing, have been extensively studied with respect to host preferences, thermal requirements, and responses to visual and chemical volatile stimuli. However, development of the psyllid in relation to the ontogeny of immature citrus flush growth has not been clearly defined or illustrated. Such information is important for determining the timing and frequency of measures used to minimize populations of the psyllid in orchards and spread of HLB. Our objective was to study how flush ontogeny influences the biotic potential of the psyllid. We divided citrus flush growth into six stages within four developmental phases: emergence (V1), development (V2 and V3), maturation (V4 and V5), and dormancy (V6). Diaphorina citri oviposition and nymph development were assessed on all flush stages in a temperature controlled room, and in a screen-house in which ambient temperatures varied. Our results show that biotic potential of Diaphorina citri is not a matter of the size or the age of the flushes (days after budbreak), but the developmental stage within its ontogeny. Females laid eggs on flush V1 to V5 only, with the time needed to commence oviposition increasing with the increasing in flush age. Stages V1, V2 and V3 were most suitable for oviposition, nymph survival and development, and adult emergence, which showed evidence of protandry. Flush shoots at emerging and developmental phases should be the focus of any chemical or biological control strategy to reduce the biotic potential of D. citri, to protect citrus tree from Liberibacter infection and to minimize HLB dissemination.