1,720,998 research outputs found
Modelling the impact of GM plants and insecticides on arthropod populations of agricultural interest
No full textMatrix population models (MPM) are nowadays not widely used to simulate arthropod population dynamics with applications to risk assessment. However, an increasing body of studies are prompting the finding of optimization techniques to reduce uncertainty in matrix parameters estimation. Indeed, uncertainty in parameters estimates may lead to significant management implications. Here we present two case studies where MPM are used for assessing the potential impact of genetically modified (GM) plants on beneficial insect species (the coccinellid Adalia bipunctata) and for evaluating spider mites (the two-spotted spider mite Teranychus urticae) resurgence after insecticide application. In both studies the data obtained, consisting of population time series, were used to generate a stage-classified projection matrix. The general model used to simulate population dynamics consists of a matrix containing (i) survival probabilities (the probability of growing and moving to the next stage and the probability of surviving and remaining in the same stage), and (ii) fecundities of the population. Most of the methods utilized for estimate the parameter values of stage-classified models rely on following cohorts of identified individuals [1]. However in these studies the observed data consisted of a time-series of population vectors n(t), for t = T0, T1, ..., Tn, where individuals are not distinguished. The relationship between the observed data and the values of the matrix parameters that produced the series involves an estimation process called inverse problem. The set of parameters that minimize the residual between the collected data and the model output for the two studies presented here was estimated using the quadratic programming method [2]. The set of estimated parameters for the A. bipunctata Rhopalosiphum maidis maize tritrophic system model supports the hypothesis that GM maize does not negatively influences A. bipunctata population growth in the tritrophic system studied [3]. Otherwise, in the case of the two-spotted spider mite resurgence, some insecticides, namely etofenprox, deltamethrin and betacifluthrin, fostered a higher mite population growth than the untreated control. This was principally due to higher adult fecundity and egg fertility, clearly explained by Life Table Response Experiments, performed starting from estimated matrices, indicating a likely trophobiotic effect. A variety of inverse modelling approaches have been applied to demographic models other than quadratic programming. Bayesian approaches [4] and evolutionary algorithms, such as Genetic Algorithms [5] have also been used for inverse modelling and parameters fitting. In order to find a better model fit for the observed stage class distributions on two case studies, we would like to explore Neural Networks or more generally machine learning possibilities in finding a set of parameter values that successfully describes observed data
Overwintering, phenology and outdoor fecundity of Harmonia axyridis in comparison with native coccinellid species in Italy.
No full textMechanical release of Phytoseiulus persimilis and Amblyseius swirskii on protected crops.
No full textThe distribution of chemicals on protected crops can be critical for the operators who are forced to make frequent treatments in an enclosed environment and in the presence of high pesticide concentrations. The introduction of organic farming techniques limits these aspects but generally requires a substantial commitment of manpower for the release of beneficial organisms resulting in high costs. To evaluate the feasibility of improving the mechanical application of beneficial organisms a mechanical blower was used. The device was previously tested in the laboratory in terms of mites survival, reproduction and distribution patterns. The application of Phytoseiulus persimilis Athias-Henriot and Amblyseius swirskii Athias-Henriot against Tetranychus urticae Koch and Frankliniella occidentalis (Pergande) on protected crops was investigated. Different application methods of the antagonists were considered: i) hand-sprinkling, ii) separate mechanical release, iii) combined mechanical release, iv) paper sachets (Swirskii- Breeding-System). Compared to hand application the mechanical release allowed a significant reduction in time needed for the dis- tribution, while showing equal pest control effectiveness. P. persimilis was able to control T. urticae adequately in all treatments, while in the case of A. swirskii release a final spinosad application became necessary to provide effective F. occidentalis control
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Influence of Mechanical Aspects of Distribution on Viability of the Biological Control Agent Steinernema carpocapsae.
No full textThe distribution of entomopathogenic nematodes (EPNs) for pest control in organic and conventional agriculture is usually carried out with traditional boom sprayers normally used for the distribution of pesticides. Nevertheless there is a reasonable possibility that this operation may induce a state of stress due to sudden pressure changes and mechanical stress, especially during the passage through the pump and nozzles or as a consequence of the effect of hydraulic or pneumatic agitation inside the tank.
This work aims to evaluate the effects of some mechanical distribution parameters on the viability of the entomopathogenic nematode Steinernema carpocapsae Weiser which may become significant during the distribution.
To assign the mechanical effects to specific components of the distribution, liquid suspensions of the nematode were subjected to different levels of static pressure, and various conditions of agitation and distribution using different types of nozzles.
Preliminary results show no significant effect of static pressure on the viability of nematodes. The passage through the nozzles and the use of a elastic rotor pump induces a 7% decrease in viability, but no difference was detected between different nozzles, while the intensity of hydraulic agitation appeared to affect the nematodes viability
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Effetti della distribuzione meccanica sulla vitalità del nematode entomopatogeno Steinernema Carpocapsae
No full textLa distribuzione di nematodi entomopatogeni (EPN) nel controllo di fitofagi in agricoltura
biologica e convenzionale è abitualmente effettuata con le comuni irroratrici impiegate per la
distribuzione di agrofarmaci. La ricerca si propone di valutare la risposta biologica, in termini
di vitalità, del nematode entomopatogeno Steinernema carpocapsae (Weiser) sottoposto a diversi effetti di stress meccanico che possono riscontrarsi nella irrorazione. In particolare, sospensioni liquide del nematode sono state sottoposte a diversi livelli di pressione statica e a diverse condizioni di agitazione e distribuzione impiegando diverse tipologie di ugelli. I risultati preliminari non mostrano un effetto significativo della pressione statica (fino a 14 bar) sulla vitalità dei nematodi. Il passaggio attraverso la pompa a girante flessibile e gli ugelli induce una diminuzione del 7% della vitalità, ma nessuna differenza si rileva tra gli ugelli utilizzati. La prova di agitazione combinata con lo svuotamento del serbatoio ha mostrato che una più bassa intensità di riciclo, realizzata, se necessario, riducendo la velocità della presa di potenza riduce la mortalità dei nematodi. In tutti i casi la concentrazione dei nematodi in corrispondenza dello svuotamento del serbatoio è stata del 20% superiore a quella iniziale
An Innovative System for Air-Assisted Distribution of Beneficial Organisms on Protected Crops.
No full textThe distribution of chemicals on protected crops is often a critical moment for the operators who are forced to make frequent treatments in an enclosed environment and in the presence of high pesticide concentrations.
The introduction of organic farming techniques improves these aspects but generally requires a substantial commitment of manpower and forces the operator to stay for a long time in environments characterized by temperature and humidity that cause discomfort and fatigue. Increasing the level of mechanization improves the effectiveness of the treatments and it
Experiments were conducted to assess the efficiency of this prototype, the reduction of working time and the possible effect on the viability of organisms distributed. also permits a quicker approach with relevant improvement on workers’ health and safety, particularly in greenhouse crops. We therefore developed a prototype for the distribution of beneficial organisms that can increase the labour productivity and distribution quality on protected crops.
The effectiveness of the distribution has been verified through laboratory and field tests to evaluate the effects of the releasing on viability and fertility of beneficial organisms.
The prototype has been demonstrated to properly perform the releasing of arthropods without compromising the viability and fertility of two species of phytoseiids (Phytoseiulus persimilis and Amblyseius swirskii), whereas in the case of nymphs of the anthocorid Orius laevigatus, the survival immediately after the distribution and the post-release survival (reaching of the adult stage) are influenced by the action of the mechanical device
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