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Temporal dynamics of Scaphoideus titanus populations: from annual occurrence patterns to changing climate suitability assessments
Get PDFA previously published model based on a time-varying distributed delay with attrition is used to simulate, at three different temporal scales (one, five and fifty-two years), the dynamics of the invasive grape leafhopper Scaphoideus titanus Ball in vineyards located in Southern and Western Switzerland. The model was parameterized with laboratory and field data. Built on population theory principles and driven by daily temperature maxima and minima and grapevine plant phenology it satisfactorily represents annual and multiannual occupancy patterns and hence, is concluded to have satisfactory predictive and explanatory capabilities. The simulations representing canopy occupancy by non-diapausing eggs, nymphs and emerging adults are particularly useful for tactical purposes including the timing of monitoring operations and insecticide applications. The simulations representing canopy occupancies by diapausing eggs, non-diapausing eggs, nymphs and adults are useful for strategic purposes. Growers and extensionists should be aware that rather stable occupancies are maintained once an area suitable for development is invaded and no management operations are undertaken. The simulations by the validated model representing long term dynamics could be useful for strategic purposes, policy design and research work. Namely, the model produces an index that represents the climate suitability of a region for colonization by S. titanus. A temporal coincidence was observed between a climate that lifted the temperatures by about 1 °C shift at the end of the 1980s and an abrupt change of the index at the Locarno-Magadino and Geneva sites. If verified at other locations, the climate suitability may have little changed after the introduction and hence, the colonized areas remained relatively constant. At the end of the 1980s, however, new areas were successfully colonized, presumably as a result of now favorable climate conditions and a sufficient dispersal ability of S. titanus. Extensionists and policy makers could take note of a future invasion and prepare growers for dealing with a new pest
Multiannual infestation patterns of grapevine plant canopy inhabiting Scaphoideus titanus Ball leafhoppers
No full textThis paper summarizes the procedures for designing, parametrizing and validating a model
representing five years infestation patterns of Scaphoideus titanus populations in grapevine plant
canopies, on the basis of temperature influences. The development of S. titanus comprises nymphs,
adults, diapausing eggs and post diapausing eggs. The basic elements of the model are temperaturedependent
i) stochastic development of the four “life stages”, ii) developmental and senescence rates,
and stage-specific survivorships, and iii) reproduction. The phenology model is based on a timevarying
delay with attrition and operates on a time step length of 1 hour. It is initialized by
proportional entries of hatching eggs resulting from a Weibull frequency distribution. Temperature
effects on the survivorship of non-diapausing life stages are modelled via attrition and on fecundity
rates via input into the diapausing egg stage. Diapausing eggs, however, do not suffer from adverse
temperature conditions. If the temperature is between 0°C and the lower developmental threshold all
life stages except the diapausing eggs suffer from an additional temperature dependent mortality. The
model is validated with observations made during five years in a Southern Switzerland (located at
Contone) vineyard. The model predictions are in agreement with the observations. The successfully
validated model will be inserted into an Adaptive Management system aiming at rationalizing pest
management and learning how the pest population system work
Multiannual infestation patterns of grapevine plant inhabiting Scaphoideus titanus (Hemiptera: Cicadellidae) leafhoppers
No full textThe Nearctic leafhopper Scaphoideus titanus Ball (Hemiptera: Cicadellidae) was accidentally introduced in Europe, where it became the vector of the ‘Candidatus Phytoplasma vitis’ phytoplasma causing the ‘Flavescence dore ́e’ disease of grapevine plants. A time-varying distributed delay model, simulating the successive occurrences of egg hatching, nymph presence, and adult emergence, is extended here to represent multi-generation infestation patterns of grapevine plants inhabited by eggs, nymphs, and adults. The model extension includes intrinsic mortality, mortality caused by plant dormancy, and low temperatures, development of diapausing and postdiapausing eggs, fecundity rates, and adult longevity. Field observations and published data were used to estimate parameters. The model was validated with five years canopy infestation data from five vineyards not subjected to insecticide treatments and found to have satisfactory explicative and predictive qualities. The model output is most sensitive to a 10% variation in the upper threshold and in the shape parameters of the survivorship function and least sensitive to a 10% variation in the shape parameters of the development function and the survivorship level. Recommendations are made to take into account other factors than temperature and plant phenology and include a wider geographical area in further model development.La cicadelle ne ́arctique Scaphoideus titanus Ball (Hemiptera: Cicadellidae) a e ́te ́ introduite
accidentellement en Europe dans les anne ́es ‘50, ou` elle est devenue le vecteur du ) Candidatus
Phytoplasma vitis * responsable de la maladie de Flavescence dore ́e de la vigne. Un mode`le de
de ́lai distribue ́ dans le temps (time-varying distributed delay model), simulant les e ́ve`nements
successifs des e ́closions, de la pre ́sence des stades juve ́niles et de l’e ́mergence des adultes, a e ́te ́
e ́tendu pour repre ́senter les niveaux d’infestation multi-ge ́ne ́rationnels de la vigne colonise ́e par des
œufs, des nymphes et des adultes. L’extension du mode`le inclut la mortalite ́ intrinse`que, la mortalite ́
cause ́e par la dormance de la plante et les basses tempe ́ratures, le de ́veloppement des œufs
diapausants et post-diapausants, les taux de fe ́condite ́ et la longe ́vite ́ des adultes. Les observations
au champ et les donne ́es publie ́es ont servi de base pour l’estimation des parame`tres du mode`le.
Le mode`le a e ́te ́ valide ́ avec les donne ́es de cinq anne ́es d’infestation de la haie foliaire de cinq
vignobles sans traitements insecticides et il a montre ́ des qualite ́s explicatives et pre ́dictives
satisfaisantes. Le re ́sultat du mode`le est plus sensible a` une variation de 10% dans le seuil supe ́rieur
et dans les parame`tres de forme de la fonction de survie et moins sensible a` une variation de
10% dans les parame`tres de forme de la fonction de de ́veloppement et du niveau de survie.
Des recommandations sont faites pour prendre en compte d’autres facteurs que la tempe ́rature
et la phe ́nologie de la plante et inclure un plus large e ́ventail de zones ge ́ographiques pour un
de ́veloppement ulte ́rieur du mode`le
Research and management oriented sampling plans for vine plant inhabiting Scaphoideus titanus Grape leafhopper nymphs
No full textThis paper summarizes the methodology used for describing the spatial distribution of the
grape leafhopper Scaphoideus titanus in a vineyard located in Southern Switzerland and presents
sampling plans for research and management purposes. The sampling technique consisted of repeated
visual counts of S. titanus nymphs. In general, a vineyard is a highly structured environment whose
influence on spatial distributions is studied by analyses of variance and quantified by regression
models developed in a stratified and multi-stage sampling universe. First, a regression model was
applied to the relationship between the proportion of infested trunk shoot leaves and the mean density
of trunk shoot leaves. This allowed the translation of a critical density for entering the vineyard in an
adaptive management (AM) program into a critical proportion. A sequential binomial sampling plan
was developed to efficiently decide whether a vineyard should be included into the AM program or
not. Second, the spatial distribution in the entire vine plant canopy was analysed. Since there were
significant differences between densities on trunk shoots and productive shoots, two different
sampling plans were designed. However, there were no significant differences between other strata
(parts of the vineyard, leaf position within shoots), so that they were disregarded in sampling plan
design. The mean crowding – mean regression model, with the intercept set to 0, indicated aggregated
distributions at the vineyard, shoot type and shoot levels. On the basis of this statistics, enumerative
and sequential sampling plans are proposed and implemented in the AM framework. The here
presented sampling techniques are advantageous over the previously used beating tray method and the
sampling plans are useful for research and management purpose
Marrying research and management activities: adaptive management of Grape leafhopper Scaphoideus titanus
No full textThis paper deals with the study and management of the Grape leafhopper Scaphoideus
titanus Ball, vector of the Candidatus Phytoplasma vitis pathogen, in vineyards located in Southern
Switzerland. S. titanus is an invasive species of North American origin that became a component of a
complex population system and an object of a complex population management set-up. Uncertainities
have been recorded in three areas: uncertainty about the observations and measurements, uncertainty
about the underlying behavior of the system and uncertainty about the environment. For dealing with
complex problems high in uncertainty, an adaptive management (AM) strategy is developed and
implemented. Progress is reported in the area of technology selection for measuring infestation levels
and temperature profiles (i), the quantitative analytical tools have been advanced as to obtain a better
insight into the dynamics of the population system (ii) and the timing of insecticide applications and
monitoring operations (iii), the ground has been solidified for the design and implementation of an
integrated population and disease transmission system (iv). The detailed presentation of the
methodologies and the results of different component studies by Rigamonti et al. (2011a; 2011b;
2013), Prevostini et al. (2013) and Trivellone et al. (2011) allows focusing on AM design,
implementation and preliminary achievements. The AM framework was concluded to be adequate for
dealing with high uncertainties associated with the complexities of the S. titanus population system
and the design and implementation of an IPM progra
Toward an improved understanding of the dynamics of vineyard-infested Scaphoideus titanus leafhopper populations for better timing of management activities
No full textBackground: This paper deals with supervised management of Scaphoideus titanus (Homoptera Cicadellidae) and describes a phenology model designed for improving the understanding of the within-vineyard dynamics and the timing of insect growth regulator (IGR) applications. RESULTS: The model consists of five components dealing with (a) the beginning of the post-dormancy development of overwintering eggs, (b) the egg hatching patterns, (c) the duration of first-instar nymphs, (d) the development and survival of subsequent instars and (e) the stochastic development of cohorts and their passage into the adult stage. Laboratory data permitted the parameterisation of temperature-dependent development and survival functions. Field data consisting mainly of beating tray catches allowed model parameterisation and validation. The model satisfactorily predicts the dynamics of age structures, the beginning as well as the pattern of egg hatching, the occurrence of the third instar and the emergence of adults. CONCLUSION: The phenology model is useful for timing IGR applications and for setting up monitoring activities in supervised S. titanus control. The model is an entry point into an adaptive management system, in that real-time weather and monitoring data are continuously integrated into the model for improving its explanatory and predictive capabilities
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
WAMS - an adaptive system for knowledge acquisition and decision support: the case of Scaphoideus titanus
No full textWAMS (Wireless-sensor-network-based Adaptive Management System) is a pest control
tool that makes continuous use of weather and pest monitoring information for the dual purpose of
improving the knowledge on pest systems and ameliorating pest management decisions. It operates at
the interface between research and pest management, establishes a close-loop between monitoring,
management and analysis of systems, and automatically improves the reliability of pest control
relevant predictions as soon as additional information becomes available. Population models, based on
time-varying distributed delays, are at the core of WAMS. The paper identifies some important
WAMS features, evaluates the predictive capabilities and its alert mechanisms as satisfactory, and
reports some preliminary experiences that reveal advantages and benefits in the areas of (i) knowledge
improvement and (ii) control rationalization. The preliminary experiences also point to some
drawbacks and shortcomings related mainly to (i) the need of a continuous engagement of actors
(growers, extensionists, applied entomologists) and (ii) the importance given to the vector in the case
of the case of an economically relevant pathogen-vector-host plant syste
New insights on Flavescence dorée phytoplasma ecology in the vineyard agro-ecosystem in southern Switzerland
Get PDFPhytoplasmas associated with Flavescence dorée (FDp) grapevine disease are quarantine pathogens controlled through mandatory measures including the prompt eradication and destruction of diseased plants, and the insecticide treatments against the insect vector, the ampelophagous leafhopper Scaphoideus titanus. In the present study, a multidisciplinary approach has been applied to investigate the FDp ecological cycle in a test vineyard agro-ecosystem in Canton Ticino, south Switzerland. Despite the scarce population density of S. titanus, a regular trend of new infections (3.4% of the total vines) through the years was observed. The leafhopper Orientus ishidae was found as the most abundant among the captured insect species known as phytoplasma vectors (245 out of 315 specimens). The population of O. ishidae was evidenced prevalently (167 specimens) in the south-western side of the vineyard and within the neighbouring forest constituted mainly by hazel (Corylus avellana) and willow (Salix spp.). These plant species were found infected by FDp related strains (30% of analysed trees) for the first time in this study. Interestingly, O. ishidae was found to harbour FDp related strains in high percentage (26% of the analysed pools). In addition, 16SrV phytoplasma group was detected for the first time in the insect Hyalesthes obsoletus and a FDp related strain in Thamnotettix dilutior, present in low populations within the test vineyard. Molecular characterisation and phylogenetic analyses of methionine aminopeptidase (map) gene sequences of FDp and related strains, here identified, revealed the great prevalence of the map-type FD2 in grapevines (97%) and in O. ishidae pools (72%). Such a map-type was found also in hazel and in T. dilutior, but not in S. titanus. Moreover, map-types FD1 and FD3 were identified for the first time in Switzerland in several host plants and phytoplasma vectors, including grapevine (FD1), S. titanus (FD1) and O. ishidae (FD1 and FD3). Based on the data obtained in this study, it is reasonable to hypothesise that the ecological cycle of FDp could be related not exclusively to the grapevine-specific feeding diet of S. titanus, but it could include other insect vector(s) and/or plant host(s). Further studies will be needed to prove the role of O. ishidae as vector able to transmit FDp from wild plants (e.g. hazel) to grapevine
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