Vector-borne Plant Diseases Research Articles

Spatial spread of infectious diseases with conditional vector preferences.

We explore the spatial spread of vector-borne infections with conditional vector preferences, meaning that vectors do not visit hosts at random. Vectors may be differentially attracted toward infected and uninfected hosts depending on whether they carry the pathogen or not. The model is expressed as a system of partial differential equations with vector diffusion. We first study the non-spatial model. We show that conditional vector preferences alone (in the absence of any epidemiological feedback on their population dynamics) may result in bistability between the disease-free equilibrium and an endemic equilibrium. A backward bifurcation may allow the disease to persist even though its basic reproductive number is less than one. Bistability can occur only if both infected and uninfected vectors prefer uninfected hosts. Back to the model with diffusion, we show that bistability in the local dynamics may generate travelling waves with either positive or negative spreading speeds, meaning that the disease either invades or retreats into space. In the monostable case, we show that the disease spreading speed depends on the preference of uninfected vectors for infected hosts, but also on the preference of infected vectors for uninfected hosts under some circumstances (when the spreading speed is not linearly determined). We discuss the implications of our results for vector-borne plant diseases, which are the main source of evidence for conditional vector preferences so far.

Phylogenetic Triage and Risk Assessment: How to Predict Emerging Phytoplasma Diseases.

Phytoplasma diseases pose a substantial threat to diverse crops of agricultural importance. Management measures are usually implemented only after the disease has already occurred. Early detection of such phytopathogens, prior to disease outbreak, has rarely been attempted, but would be highly beneficial for phytosanitary risk assessment, disease prevention and mitigation. In this study, we present the implementation of a recently proposed proactive disease management protocol (DAMA: Document, Assess, Monitor, Act) for a group of vector-borne phytopathogens. We used insect samples collected during a recent biomonitoring program in southern Germany to screen for the presence of phytoplasmas. Insects were collected with malaise traps in different agricultural settings. DNA was extracted from these mass trap samples and subjected to PCR-based phytoplasma detection and mitochondrial cytochrome c oxidase subunit I (COI) metabarcoding. Phytoplasma DNA was detected in two out of the 152 insect samples analyzed. Phytoplasma identification was performed using iPhyClassifier based on 16S rRNA gene sequence and the detected phytoplasmas were assigned to 'Candidatus Phytoplasma asteris'-related strains. Insect species in the sample were identified by DNA metabarcoding. By using established databases, checklists, and archives, we documented historical associations and records of phytoplasmas and its hosts in the study region. For the assessment in the DAMA protocol, phylogenetic triage was performed in order to determine the risk for tri-trophic interactions (plant-insect-phytoplasma) and associated disease outbreaks in the study region. A phylogenetic heat map constitutes the basis for risk assessment and was used here to identify a minimum number of seven leafhopper species suggested to be monitored by stakeholders in this region. A proactive stance in monitoring changing patterns of association between hosts and pathogens can be a cornerstone in capabilities to prevent future phytoplasma disease outbreaks. To the best of our knowledge, this is the first time that the DAMA protocol has been applied in the field of phytopathology and vector-borne plant diseases.

Analysis of a Mathematical Model Arising in Plant Disease Epidemiology

In this work we study from the mathematical and numerical point of view a problem arising in vector-borne plant diseases. The model is written as a nonlinear system composed of a parabolic partial differential equation for the vector abundance function and a first-order ordinary differential equation for the plant health function. An existence and uniqueness result is proved using backward finite differences, uniform estimates and passing to the limit. The regularity of the solution is also obtained. Then, using the finite element method and the implicit Euler scheme, fully discrete approximations are introduced. A discrete stability property and a main a priori error estimates result are proved using a discrete version of Gronwall’s lemma and some estimates on the different approaches. Finally, some numerical results, in one and two dimensions, are presented to demonstrate the accuracy of the approximation and the behaviour of the solution.

Modeling and Analysis of Vector-borne Plant Disease with Two Delays

In this paper, a non-linear mathematical model is formulated and analyzed to understand the dynamics of plant disease in presence of predators. Here predators act as biological control agent that reduce the vectors carrying the disease pathogen. The mathematical model is formulated using system of delay differential equations by considering two delays. The delays are time taken for the plant to become infected after contagion and time taken for the insect to become infected after contagion. The existence and stability of different equilibria of the model are discussed in detail. The basic reproduction number R 0 is computed. The Routh-Hurwitz criteria is used to investigate the stability of the disease-free equilibrium and the endemic equilibrium in absence of delay. The stability of endemic equilibrium is also investigated in presence of delay. The occurrence of Hopf-bifurcation is demonstrated by considering the delay as the bifurcation parameter. The critical values of the delays are obtained which preserve the stability of the endemic equilibrium point. The model system shows an oscillatory behavior beyond this critical values of delays. Numerical simulation is also performed to support the analytical results. It is found that biological control has positive impact on reducing the transmission of plant disease.

Dynamics of a delayed plant disease model with Beddington-DeAngelis disease transmission.

In the present research, we study a mathematical model for vector-borne plant disease with the plant resistance to disease and vector crowding effect and propose using Beddington-DeAngelis type disease transmission and incubation delay. Existence and stability of the equilibria have been studied using basic reproduction number ($ \mathcal{R}_0 $). The region of stability of the different equilibria is presented and the impact of important parameters has been discussed. The results obtained suggest that disease transmission depends on the plant resistance and incubation delay. The delay and resistance rate can stabilise the system and plant epidemic can be avoided increasing plant resistance and incubation period.

Modeling plant virus propagation with Filippov control

Plants play a vital role in the everyday life of all organisms on earth. This paper proposes a Filippov vector-borne plant disease model incorporating roguing of infected plants and spaying pesticides to relieve the economical devastation for growers and damage to humans, natural enemies and the environment. No control strategy is taken if the number of infected plants is less than an infected plant threshold level I_{c}; further, infected plants are removed once the number of infected plants exceeds I_{c}; meanwhile, pesticides are spayed if the number of infected vectors exceeds the infected vector threshold level Y_{c}. The global dynamics for the proposed system is investigated. Model solutions ultimately stabilize at the positive equilibrium that lies in the region above I_{c}, or on I=I_{c}, or below I_{c}, depending on the threshold values I_{c} and Y_{c}. The findings indicate that proper combinations of the infected plant and vector threshold values based on the threshold policy can maintain the number of infected plants either at a previously given level or below a certain threshold level.

Numerical Analysis of Stochastic Vector Borne Plant Disease Model

We are associating the solutions of stochastic and deterministic vector borne plant disease model in this manuscript. The dynamics of plant model depends upon threshold number P∗. If P∗ 1 explains the persistence of disea... | Find, read and cite all the research you need on Tech Science Press

Impact of incubation delay in plant–vector interaction

Knowledge of the incubation period of infectious diseases is crucial to our understanding of epidemiological phenomena and for the design of appropriate prevention and control policies. In this article, a mathematical model has been formulated for the transmission dynamics of vector-borne plant disease considering incubation period as the time delay factor. Existence of the equilibria and their stability has been studied on the basis of basic reproduction number. The region of stability of the steady states is presented in different parameter subspaces. Stability changes occur through Hopf bifurcation in both the delayed and nondelayed system. Analytical and numerical findings suggest that the role of incubation delay is stabilising the coexistence equilibrium and epidemics can be successful if host plant has shorter incubation period.

Global Dynamic Analysis of a Vector-Borne Plant Disease Model with Discontinuous Treatment

This paper proposes a vector-borne plant disease model with discontinuous treatment strategies. Constructing Lyapunov function and applying non-smooth theory to analyze discontinuous differential equations, the basic reproductive number R0 is proved, which determines whether the plant disease will be extinct or not. If R0 R0 > 1 , there exists a unique endemic equilibrium which is globally stable. The numerical simulations are provided to verify our theoretical results, which indicate that after infective individuals reach some level, strengthening treatment measures is proved to be beneficial in controlling disease transmission.

Mathematical models are a powerful method to understand and control the spread of Huanglongbing.

Huanglongbing (HLB), or citrus greening, is a global citrus disease occurring in almost all citrus growing regions. It causes substantial economic burdens to individual growers, citrus industries and governments. Successful management strategies to reduce disease burden are desperately needed but with so many possible interventions and combinations thereof it is difficult to know which are worthwhile or cost-effective. We review how mathematical models have yielded useful insights into controlling disease spread for other vector-borne plant diseases, and the small number of mathematical models of HLB. We adapt a malaria model to HLB, by including temperature-dependent psyllid traits, “flushing” of trees, and economic costs, to show how models can be used to highlight the parameters that require more data collection or that should be targeted for intervention. We analyze the most common intervention strategy, insecticide spraying, to determine the most cost-effective spraying strategy. We find that fecundity and feeding rate of the vector require more experimental data collection, for wider temperatures ranges. Also, the best strategy for insecticide intervention is to spray for more days rather than pay extra for a more efficient spray. We conclude that mathematical models are able to provide useful recommendations for managing HLB spread.

Mathematical Model of Vector-Borne Plant Disease with Memory on the Host and the Vector

Mathematical Model of Vector-Borne Plant Disease with Memory on the Host and the Vector

Use the insiders: could insect facultative symbionts control vector-borne plant diseases?

Insect vector-borne plant diseases, particularly those whose causative agents are viral, or phloem- and xylem-restricted bacteria, greatly impact crop losses. Since plants are immobile, the epidemiology of vector-borne diseases greatly depends on insect vectors, which are the only means of dissemination for many pathogens. The effectiveness of a vector-borne pathogen relies upon the vectorial capacity, which is affected by vector density, feeding activity on hosts, longevity before and after pathogen ingestion, duration of the incubation period, and vector competence. During the last decade, research on human vector-borne epidemics has stimulated interest in novel control strategies targeting different parts of the vector cycle, and our purpose here is to draw parallels between this field of research and agronomy. We review the literature on insect vectors of crop diseases and their symbiotic microorganisms with the aim of suggesting future integrated management techniques based on current research on insect-vectored human diseases. Vector transmission is a complex process and different modes of transmission are encountered irrespective of the pathogen. Facultative symbionts have varied effects on life history traits that could be used for vector population control. Symbiont selection, transformation, and their manner of dissemination are important when developing an integrated vector management system based on symbiont manipulation. In the short term, progress on our knowledge of the microflora of insect vectors of plant diseases must be made. In the long term, symbiont manipulation, which has been successfully demonstrated against human insect-vectored diseases, could be adapted to insect-borne plant diseases to increase sustainable crop production.

Global dynamic analysis of a vector-borne plant disease model

An epidemic model which describes vector-borne plant diseases is proposed with the aim to investigate the effect of insect vectors on the spread of plant diseases. Firstly, the analytical formula for the basic reproduction number R0 is obtained by using the next generation matrix method, and then the existence of disease-free equilibrium and endemic equilibrium is discussed. Secondly, by constructing a suitable Lyapunov function and employing the theory of additive compound matrices, the threshold for the dynamics is obtained. If R0 ≤ 1, then the disease-free equilibrium is globally asymptotically stable, which means that the plant disease will disappear eventually; if R0 > 1, then the endemic equilibrium is globally asymptotically stable, which indicates that the plant disease will persist for all time. Finally some numerical investigations are provided to verify our theoretical results, and the biological implications of the main results are briefly discussed in the last section.

Effects of pymetrozine, an antifeedant of Hemiptera, on Asian citrus psyllid, Diaphorina citri, feeding behavior, survival and transmission of Candidatus Liberibacter asiaticus

Vector-borne plant disease management can be enhanced by deployment of antifeedants in addition to the use of broad-spectrum neurotoxic insecticides. The effects of pymetrozine on Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, feeding behaviour, survival and transmission of Candidatus Liberibacter asiaticus (Las), the presumed causal pathogen of huanglongbing, were investigated. Pymetrozine applied at 52 and 104 µg mL(-1) to citrus plants [Swingle citrumelo (X Citroncirus webberi Ingram and Moore)] modified the feeding behavior of ACP and increased the amount of time spent performing non-penetration behaviors while decreasing the time spent performing ingestion behaviors compared with the controls 1 day after treatment. However, the antifeedant effect of pymetrozine subsided 5 days after application. Pymetrozine reduced the survival of both adults and nymphs on treated plants compared with the control. However, it had a greater impact on survival of nymphs than on survival of adults. Pymetrozine applied at 52 and 104 µg mL(-1) on Las-infected 'Valencia' sweet orange plants [Citrus sinensis L. (Osbeck)] reduced acquisition (12 and 21% respectively) and transmission (11 and 18% respectively) of Las by feeding ACP adults compared with the controls; however, these reductions were not statistically significant. Pymetrozine exhibited moderate antifeedant effects by modifying the feeding behavior of ACP adults with short residual activity. The impact of pymetrozine on survival of nymphs was greater than on adults at the higher concentrations tested. Pymetrozine also reduced the acquisition and transmission of Las by feeding ACP adults up to 21 and 18%, respectively, compared with untreated controls.

Insect Transmission of Plant Pathogens

MUCHOF BIOLOGICAL RESEARCHCONDUCTED TODAY ismultidisciplinary, partly because of the availability of ever simpler to use molecular tools and the realization that ecological systems are complex and multitrophic. Although there is a general trend toward academic specialization and cooperation, some Þelds still require that scientists be aware of the “bigger picture.” We consider that the study of insect-transmitted plant pathogens is one of those Þelds, where insect, pathogen, and plant are inseparably linked. In this triangle of interactions, researchers focus their interests on questions at the molecular and cellular to epidemiological levels. Throughout the years, plant vector entomologists have addressed a variety of important pest problems, often linking entomologists and plant pathologists for the development of improved and sustainable disease control strategies. In this issue of the Annals of the Entomological Society of America, the Cc subsection (Arthropods in Relation to Plant Disease) of the Society honors two of its members, Lowell R. “Skip” Nault and Alexander H. “Sandy” Purcell. Skip and Sandy have been recognized as two of the ESAOs preeminent plant vector entomologists. They were also partly responsible for training and motivating a new generation of scientists involved in vectorÐphytopathogen relationships. What made their contribution, recognized by tribute symposia at recent ESA meetings, so remarkable was their ability to study problems as multitrophic interactions, incorporating aspects of diverse research areas into their work as needed. Their contributions ranged from disease epidemiology and modeling to insect biology; from insect microbial ecology to bacterial genomics. The interests of Skip and Sandy merged in what might be labeled “ecology of insectborne plant diseases.” In fact, they have written or coauthored several articles on the topic. To understand the ecology of such diseases, one must know how insects transmit plant disease agents and then incorporate that knowledge into vector ecology, crop management practices, and disease development and spread. This holistic approach to vector research, difÞcult to establish for various reasons, led to numerous academic and applied breakthroughs by both researchers. Skip was an advisor, mentor, collaborator, and colleague tomanywhowandered throughhis door at one time or another during his tenure at The Ohio State University. Originally an aphidologist out of SylvesterOs laboratory, Skip saw the light and began working with leafhopper-transmittedmollicutes andviruses. In the course of his 30-yr career at the Ohio Agricultural Research and Development Center in Wooster, OH, Skip not only focused on vectorÐpathogen relationships but also ventured into new areas such as leafhopper communication, feeding behavior, and ecology, primarily through his many students and postdoctoral workers. In all, Skip trained 18 masters and doctoral students and published more than 120 refereed articles in various scientiÞc journals. A great thinker, Skip liked to synthesize new ideas and hypotheses to test. Among his most lasting contributions are his early work with aphid alarm pheromones,DalbulusÐmaize evolution concepts, and the synopses of plant virus modes of transmission. During his 30 yr as a faculty member at the University of California, Berkeley, Sandy incited interest of students, collaborators, and colleagues on various topics associated with vector-borne plant diseases. The never-ending interest he had toward all areas of science and his willingness to discuss academic questions and ideas have motivated students and colleagues worldwide. Sandy headed research that identiÞed the etiological agent of PierceOs disease of grape and other plant diseases, the bacterium Xylella fastidiosa; studied its vector transmission characteristics; and improved our understanding on the ecology and epidemiology of this pathogen. Plant pathogenic mollicutes (phytoplasmas and spiroplasmas) and their interactions with their leafhopper hosts also were continuous components of his research. Another line of SandyOs research was insect symbiosis, primarily facultative symbionts of the pea aphid, Acyrthosiphon pisum (Harris). Thewide range of tools used by Sandy to address unique ecological questions also was a hallmark of his contributions. Members of the Cc subsection have submitted manuscripts representing many, but by no means all, research areas worked on by these two researchers. Themanuscripts alsodemonstrate thebreadthofplant vector entomology and its importance in linking entomology and plant pathology in search of betterways to control insect-borne plant diseases. Finally, we are grateful to all those who served as reviewers for these manuscripts. Their thoughtful comments were essential for improvements in the Þnal presentation. 1 Department of Plant and Environmental Protection Sciences, University of Hawaii at Manoa, Honolulu, HI 96822. 2 Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078. 3 USDAÐAPHIS, 41-650 Ahiki Street, Waimanalo, HI 96795.