Vectors Of Plant Diseases Research Articles

Effects of Cold-Acclimation, Pathogen Infection, and Varying Temperatures on Insecticide Susceptibility, Feeding, and Detoxifying Enzyme Levels inDiaphorina citri(Hemiptera: Liviidae)

Abstract Infection of Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), with ‘Candidatus' Liberibacter asiaticus (Las), the causal pathogen of citrus greening disease or huanglongbing, increases psyllid susceptibility to insecticides. Diaphorina citri populations in citrus occur year-round in tropical and sub-tropical habitats, and thus insecticide applications for managing this plant disease vector occur over a wide temperature range (10–40 °C). During the winter season, D. citri is occasionally exposed to periods of freezing temperatures, when temperatures fall below -6.5 °C. In this investigation, we compared insecticide susceptibility of uninfected and Las-infected D. citri at various temperatures (20–37 °C). Cold-acclimated (6 ± 1 °C) D. citri adults were less susceptible to neonicotinoid insecticides as compared with non-acclimated controls, but this trend was not observed for other insecticides tested. A positive correlation between temperature and percentage mortality caused b...

Feeding behaviour of a virus‐vector leafhopper on host and non‐host plants characterised by electrical penetration graphs

AbstractMany sap‐feeders are vectors of plant diseases, acquiring and inoculating pathogens at various stages of the feeding process. In oligophagous species, certain aspects of probing behaviour on hosts and non‐hosts may have implications for the range of both pathogens and plants that can be inoculated. We addressed the question of which probing phases (including ingestion) occur on non‐host plants in the case of the common leafhopper Psammotettix alienus (Dahlbom) (Hemiptera: Cicadellidae). This species is a pest on cereals, a vector of the Wheat dwarf virus, and possible carrier of other pathogens. It is regarded as oligophagous on grasses, but has been reported also on other plant families. In a combined electrical penetration graph (EPG) video observation study, we aimed to give a description of the waveforms during the probing process. EPG recordings were made on a suitable host, barley, Hordeum vulgare L. (Poaceae), and on two non‐host plants, the sedge Carex tomentosa L. (Cyperaceae) and the ragweed Ambrosia artemisiifolia L. (Asteraceae). We demonstrated that P. alienus probes on plants other than Poaceae, including dicotyledons. Univariate and multivariate analyses of general probing variables revealed that total and maximal probe durations were shorter and probing progress less advanced on non‐host plants. Waveforms of the pathway phase were stereotypical and statistically not different between the host and non‐host plants. On sedge, the waveform signifying insertion through the plant epidermis was shortened but much more frequent, indicating penetration difficulties and retrials. Most importantly, waveforms indicating phloem ingestion were not present on either of the non‐host plants. Non‐host probing events terminating during the pathway phase suggested that rejection occurred when the stylets were in the mesophyllum. Overall, the EPG signals reflected the unsuitability of A. artemisiifolia and C. tomentosa compared to barley, but the occurrence of probing and the demonstrated level of probing progress imply that pathogen transmission cannot be excluded in the case of many non‐host plants and non‐specific pathogens.

Tuta absolutaMeyrick (Lepidoptera: Gelechiidae): A New Threat to Tomato Production in Sub-Saharan Africa

In sub-SaharanAfrica, vegetable crops are an essential component of sustainable development, with a significant contribution to food security and nutritional balance, but also an important source of income for resource-poor growers, especially in urban and peri-urban areas (FAO 2012). However, a major constraint to growing field horticultural crops is the reduction in yield and quality caused by insect pests by direct feeding or as plant disease vectors (James et al. 2010; Ekesi et al. 2011). Chemical control is the main control strategy implemented by growers to cope with insect pests (Ngowi et al. 2007; Grzywacz et al. 2010). Extensive and sometimes inappropriate use of chemical insecticides to control insect pests increases production costs and negatively impacts food safety (residues), human health and environment, especially biodiversity and beneficial arthropods (Desneux et al. 2007; Biondi et al. 2012). The implementation of effective and ecologically-sound integrated pest management (IPM) strategies is needed to develop sustainable vegetable production.

Integrating vibrational signals, mitochondrial DNA and morphology for species determination in the genus Aphrodes (Hemiptera: Cicadellidae)

AbstractReliable delimitation and identification of species is central not only to systematics, but also to studies of biodiversity, ecology and pest management. In the era of Internet‐based biodiversity databases misidentifications are rapidly disseminated and may have far‐reaching consequences. Leafhoppers from the genus Aphrodes (Hemiptera, Cicadellidae) are common and abundant, but, nevertheless, they are still a taxonomically challenging group whose members are often assessed in ecological studies and are also potential vectors of plant diseases. Previous study has shown that the syntype series for A. aestuarina (Edwards) includes also specimens of A. makarovi Zachvatkin and has suggested that misidentifications may be widespread in museum collections. We studied Aphrodes individuals collected from the U.K. and Slovenia in order to provide a more comprehensive analysis of this genus using multiple criteria. Combined work using male and female vibrational signals emitted during courtship, and a 600‐bp fragment within the barcoding region of the COI mtDNA gene, provided validated specimens that we also used for morphometric study. Analyses confirmed A. aestuarina, A. bicincta, A. diminuta and A. makarovi as behaviourally, genetically and morphologically distinct species. Although any of these approaches could be used alone to distinguish between species, combining morphological and molecular approaches will help to improve reliability, especially when identifying females. Morphological investigation of validated individuals from the U.K. and Slovenia also revealed geographic differences within species. By combining several body and aedeagus morphological characters males can be reliably identified, however, morphological differences between species are, nevertheless, relatively small. By contrast, observed genetic distances between Aphrodes species are relatively large (4.2–7.0%). At about half of our collecting sites more than one Aphrodes species was found and A. makarovi was collected together with every other species, including A. aestuarina on tidal saltmarshes. Due to low morphological variation between syntopic congeners it is likely that many museum specimens of Aphrodes have been assigned to the wrong species and species identification in ecological and vector studies may also be questionable.

Population genetics suggest that multiple invasion processes need to be addressed in the management plan of a plant disease vector

The use of a multidisciplinary approach is becoming increasingly important when developing management strategies that mitigate the economic and biological costs associated with invasive pests. A framework of simulated dispersal is combined with life-history information and analyses of population genetic structure to investigate the invasion dynamics of a plant disease vector, the island sugarcane planthopper (Eumetopina flavipes), through an archipelago of significant Australian quarantine concern. Analysis of eight microsatellite loci from 648 individuals suggests that frequent, wind-assisted immigration from multiple sources in Papua New Guinea contributes significantly to repeated colonization of far northern islands. However, intermittent wind-assisted immigration better explains patterns of genetic diversity and structure in the southern islands and on the tip of mainland Australia. Significant population structuring associated with the presence of clusters of highly related individuals results from breeding in-situ following colonization, with little postestablishment movement. Results also suggest that less important secondary movements occur between islands; these appear to be human mediated and restricted by quarantine zones. Control of the planthopper may be very difficult on islands close to Papua New Guinea given the apparent propensity for multiple invasion, but may be achievable further south where local populations appear highly independent and isolated.

Role of Elicitors in Inducing Resistance in Plants against Pathogen Infection: A Review.

Disease control is largely based on the use of fungicides, bactericides, and insecticides—chemical compounds toxic to plant invaders, causative agents, or vectors of plant diseases. However, the hazardous effect of these chemicals or their degradation products on the environment and human health strongly necessitates the search for new, harmless means of disease control. There must be some natural phenomenon of induced resistance to protect plants from disease. Elicitors are compounds, which activate chemical defense in plants. Various biosynthetic pathways are activated in treated plants depending on the compound used. Commonly tested chemical elicitors are salicylic acid, methyl salicylate, benzothiadiazole, benzoic acid, chitosan, and so forth which affect production of phenolic compounds and activation of various defense-related enzymes in plants. Their introduction into agricultural practice could minimize the scope of chemical control, thus contributing to the development of sustainable agriculture. This paper chiefly highlights the uses of elicitors aiming to draw sufficient attention of researchers to the frontier research needed in this context.

Vectors and Vector-Borne Diseases in Turkey

In Turkey, arthropod-borne diseases such as human babesiosis, dirofilariasis, leishmaniasis, malaria, lymphatic filariasis, onchocerciasis, anthrax, bartonellosis, louse-borne relapsing fever, lyme disease, plague, trench fever, tularemia, epidemic typhus, tick-borne typhus, Crimean-Congo hemorrhagic fever, phlebovirus infections, tick-borne encephalitis and west nile virus in humans; animal trypanosomiasis, avian haemosporidiasis, babesiosis, canine hepatozoonosis, canine lesihmaniosis, dipetalonemiasis, dirofilariosis, habronemiasis, onchocerciasis, parafilariasis, setariasis, theileriosis, thelaziasis, anaplasmosis, ehrlichiosis, feline infectious anemia, akabane, bluetongue, bovine ephemeral fever, equine infectious anemia, louping ill, west nile virus, colony collapse disorders (CCD) were reported in domestic animals and Wolbachia endobacteria infection was also reported in mosquitos so far. On the other hand, aphids (Aphididae), leafhoppers (Cicadellidae), white flies (Aleyrodidae), beetles (Coleoptera), trips (Thysanoptera), gal mites (Eriophyidae), and nematodes are also very important vectors of plant diseases in Turkey. Some of the most harmful plant viruses in the world such as tristeza, plum pox virus, and tomato ringspot viruses are also transmitted by arthropod vectors. In recent years, in spite of changes in ecological balance caused by abandoning agricultural land, use of natural areas to farm, release of rabbits, preventing water flooding, leaving the fields uncultivated, migration from urban to rural areas, hunting of wild animals, the dramatic drop in the number of farm animals, global warming and the strengthening of wild life was probably responsible for the increase of tick populations. The construction of ponds and dams, changes in riverbeds, drying out of swamps and marshes, dense ad-hoc and haphazard construction, changes in picnicking habits, wild irrigation in agriculture, and the use of unsuitable control measures by local authorities, resulted in an increase of flies. This led to an increase in infected vector populations and vector-borne diseases and a decrease in the potential for economic development. In conclusion, it is very important to initiate and develop integrated control programs targeting arthropod vectors, disease agents of human, animal and plants and natural reservoirs. These diseases have been caused high economic losses in Turkey, and therefore they should be further investigated

Diversidade de Hemiptera Auchenorrhyncha em citros, café e fragmento de floresta nativa do Estado de São Paulo

The population of Hemiptera Auchenorrhyncha was studied in sweet citrus groves (Citrus sinensis), coffee plantations (Coffea arabica) and a semi-deciduous seasonal forest with shrub physiognomy in Bebedouro, SP, to evaluate the influence of the natural ecosystem on the species composition of the agroecosystems. Monitoring was carried out by using yellow stick cards, which were replaced every 15 days and all Auchenorrhyncha collected were counted and identified. Seven families, 11 subfamilies and 98 species were collected, with Cicadellidae being the most abundant. The native forest presented larger wealth, diversity and equitability of Auchenorrhyncha species, demonstrating to be more stable than the other habitats. The high values of similarities obtained between the agroecosystems and the forest demonstrated that great part of Auchenorrhyncha species occurring in the agricultural habitats was also occurring at the forest, indicating that the last may serve as reservoir of species. The abundance of the taxonomic groups of Auchenorrhyncha collected varied with the evaluated habitats, with Proconiini being the most abundant in the coffee plantation next to the forest, Athysanini, Scaphytopiini, Neocoelidiinae and Coelidiinae in the orange orchard and coffee plantation distant from the forest; Cicadellinae and Agalliinae were not related to any of the habitats. The presence of vector insects and possible vectors of plant diseases in the appraised habitats indicate the need of the implementation of strategies for landscape management.

Heteroptera as vectors of plant pathogens

The ability of piercing-sucking insects to transmit plant disease is closely linked to feeding mode and target tissue. The true bugs (Heteroptera) are generally considered to be of minimal importance as vectors of plant pathogens, although they share similar feeding behaviors with homopterans. Modes of feeding in Heteroptera include "lacerate-and-flush", intracellular penetration to vascular tissue, and an osmotic pump mechanism to acquire cell contents without penetrating the cell membrane. The relationship between heteropteran taxonomy, feeding mode, and the type of pathogens transmitted is explored through a literature survey of feeding behavior and vectoring capability. Transmission by true bugs of fungal pathogens, bacteria, viruses, phytoplasmas, and trypanosomatid flagellatesis summarized; no records exist of bugs transmitting spiroplasmas. Trypanosomatid flagellates of plants appear to be harbored or transmitted exclusively by Pentatomomorpha (Lygaeioidea, Coreoidea, Pentatomoidea, and Pyrrhocoroidea). Bacterial and fungal transmission occurs among families representing both infraorders of phytophagous Heteroptera, but Miridae (Cimicomorpha) are most closely associated with bacteria, whereas Pentatomidae and Coreidae (Pentatomomorpha) predominate in transmission of fungi. Few cases of transmission of phytoplasmas and viruses are documented, but Cimicomorpha (traditionally categorized as destructive lacerate-and-flush feeders) are represented more frequently than expected, considering the tissue specificity of these pathogens. Literature emphasis on the exclusive or predominant role of homopterans as disease vectors may discourage initial investigations of true bugs; based on the results presented here, the necessity of including heteropterans in any survey of potential plant disease vectors is clear.

Long PCR Is a Sensitive Method for Detecting Liberobacter asiaticum in Parasitoids Undergoing Risk Assessment in Quarantine

Abstract The accidental importation of plant pathogens in or on the bodies of parasitoids imported as natural enemies has been raised as a potential risk of classical biological control projects involving insects that serve as vectors of plant diseases. During quarantine evaluation of two parasitoids, Tamarixia radiata Waterston and Diaphorencyrtus aligarhensis (Shafee, Alam and Agarwal), imported for classical biological control of Asian citrus psylla Diaphorina citri (Kuwayama) in Florida, we were asked to determine whether these parasitoids were free of the causal agent of Asian greening disease, the bacterium Liberobacter asiaticum. Preliminary tests with allele-specific polymerase chain reaction (Standard PCR) suggested that the assays were prone to false negatives. Another PCR protocol, Long PCR, previously was shown to be more reliable than Standard PCR for screening of insects for another bacterium ( Wolbachia ). The sensitivity of Long and Standard PCR protocols was compared by use of plasmid DNA containing two DNA fragments from the greening disease agent or plasmid mixed with DNA extracted from host plants, psyllids, or parasitoids. Results indicated that inhibitors of the PCR were present in both plant and insect DNA, making the Standard PCR relatively insensitive and allowing high levels of false negatives. Long PCR, which incorporates a second DNA polymerase with proof-reading activity, yielded consistent results and was orders of magnitude more sensitive than the Standard PCR. As few as 100 copies of plasmid mixed with either plant or insect DNA consistently could be detected. Long PCR assays conducted on pooled and individual T. radiata and D. aligarhensis, their psyllid hosts, or their host plants over a period of 6 months failed to produce any positives, indicating that release of these two parasitoids should elicit little concern that greening bacteria would be introduced accidentally into Florida through this classical biological control program.

Role of Ants in Pest Management

Ants, with an estimated world population of 1015 adults (188), are most abundant in the tropics where in rain forests they may represent between one third and half of the insect biomass (32). About two hundred species of ants have been recorded in one locality in Papua New Guinea (187), and they also retain rich diversity in some tropical crops (76, 134). In general, ants are less common, with fewer species, outside the tropics (120, 187), but they may still be ecologically important, as in a European grassland where about 140 workers per m2 consumed approximately 200 times their biomass annually (71). They are usually least common and diverse in disturbed arable habitats (120). In view of their abundance, their stability as populations, and their feeding habits, ants have a major influence in many habitats (17,30,45,59,63, 118, 127, 188). As predators of pests, they may be useful in pest management, but such positive attributes must be weighed against possible disadvantages. Besides acting as biological-control agents, some ants are important in pollination, soil improvement, and nutrient cycling (45). In contrast, some feed on or disturb plants and may act as vectors of plant diseases, benefit

The biology of the Psylloidea (Homoptera): a review

AbstractPsyllids are generally narrowly host specific and are restricted almost exclusively to perennial dicotyledenous plants. Psyllids are known vectors of plant diseases. In addition, the effects of salivary injection can be very severe, causing growth abnormalities in the plant. Psyllid development rates are related to the nutritive status of the host-plant and, as in aphids, the honeydew produced while feeding is low in nitrogen. Psyllids reproduce sexually and pass through five nymphal instars before becoming adult. The immature stages exhibit both morphological and behavioural adaptations to resist desiccation, and the life-cycle is often highly synchronised with host-plant phenology. Adult Psyllids are known to disperse up to eight miles on wind currents, although in general dispersal is less marked than in aphids. The mechanism of host-plant selection is probably chemo-gustatory. Capacity for population increase in Psyllids is more dependent on generation time than on female fecundity. Recorded Psyllid parasites include Diptera of the family Cecidomyiidae and a wide range of Hymenoptera. These parasite species are almost exclusively parasitic on Psyllids although there is little evidence for parasite–host specificity within the Psylloidea. Psyllid species from a wide range of geographical areas have similar predator complexes. Anthocorids, Syrphids, Coccinellids and Neuroptera larvae are the main predators. At high population densities nymphal mortality increases in a density-dependent manner with increasing density, whereas at low densities nymphal survival is enhanced by group feeding. Close parallels exist in the feeding biology of aphids and Psyllids, but aphids appear better adapted for the exploitation of unstable ephemeral food sources.

Dispersal and Quality in Populations of Cicadulina Species (Cicadellidae)

Cicadulina species are found in grasses in many parts of the tropical and warm temperate parts of the world. Ruppel (1965) recognizes thirteen different species and most of these are of economic importance, either confirmed or suspected of being vectors of plant diseases. Five species have been shown to be vectors of miaize streak, a disease which is a cause of crop losses in eastern and southern Africa (Nielson 1968). Three of these, C. mbila (Naude), C. parazeae Ghauri, and C. storeyi China are the principal vectors of the disease in Rhodesia (Rose 1963). Field observations have indicated that Cicadulina leafhoppers fly two very different kinds of distances. Many fly only a few metres and there is a sharp fall in numbers captured on trap plants with distance from the edge of a breeding source. During the main flight season, however, Cicadulina are captured in suction traps 20 m above the ground and there is widespread invasion of cereal crops by leafhoppers dispersing from low density populations in drying grasses. These two levels of dispersal are also indicated by the differences in the patterns of streak disease which are found during the main flight period in the dry season and on irrigation areas in the summer (Rose 1971). Although these patterns are partly explained by increases in numbers of Cicadulina emerging from grasses at the end of the summer, they may also be due to changes in quality of populations within the grasses. Changes in qualities such as size, wing length, colour and activity are known to be caused in populations of many different insects as responses to effects produced by the environment (Uvarov 1921; Faure 1932, 1943). The mass of information that has been collected on morphological and behavioural polymorphism is thoroughly discussed by Johnson (1969) who stresses its significance as it affects the dispersal of insects. He concludes that it 'seems that the proportion of migrants in a population may be determined not only by ontogenetic effects produced by adverse changes or associated token stimuli in the environment but also by selection from particularly vigorous females from one generation to another'. A laboratory method was required in order to find out more about the conditions that affect flight and flight duration in the three Cicadulina species. Flying Cicadulina tethered to pins proved to be satisfactory.

Aphid Responses to Colors in Artificial Rearings

Introduction My interest in aphid responses to colors dates back to 1963 when the rearing of aphids on synthetic diets was progressing with difficulty at St. Jean. The solution to the problem of rearing aphids and, in general, of several homoptcrous vectors of plant diseases has been attempted with more or less success by several people over the past forty years (Carter 1927, 1928), (Hamilton 1930, 1935), (Pletsch 1937), and my former colleague Maltais (1952). Mittler and Dadd (1962) had just published their pioneer paper on the artificial feeding of Myzus persieae (Sulzer). However, no definite method or diet was apparently satisfactory for our pea aphids, Acyrthosiphon pisum (Harris). It was a frustrating period in spite of deep meditations and “imagineering,” and hard hopes. I welcome the opportunity to talk to you during this symposium about the evolution of my ideas and laboratory methods which, over the past two years, have made possible the first study of color responses of winged and apterous aphids in vitro. The classical works of V. Moericke (1952) demonstrated that in nature winged aphids were attracted to yellow surfaces. Aphid flight was also investigated by J. S. Kennedy and his associates and reviewed by Kennedy and Stroyan (1959).

Distribution of Leafhopper Vectors of Plant Diseases in Michigan

Distribution of Leafhopper Vectors of Plant Diseases in Michigan

Economic Application of Insect-Association Studies

Studies of insect associations supplement standard methods in economic entomology. They provide data on biology of species, host-plant relationships, relations between climate and species, cyclic phenomena, plant-disease vectors, and the control of waste lands as reservoirs for economic and potentially economic insects.