HOVER-WINTER : un modèle multi-agent pour simuler la dynamique hivernale d'un insecte auxiliaire des cultures (Episyrphus balteatus, Diptera: Syrphidae) dans un paysage hétérogène

Comprendre l'influence de l'hétérogénéité dans le paysage sur la dynamique de population est nécessaire dans le domaine de la lutte biologique par conservation et gestion des habitats. Un paysage hétérogène se définit comme une mosaïque plus ou moins structurée d'unités paysagères possédant chacune différents types et niveaux de ressources. Dans le cas des insectes auxiliaires de culture hivernants, la survie passe souvent par la possibilité d'exploiter simultanément plusieurs ressources dans le paysage. Dans le cadre de cette thèse, nous avons développé une approche modélisatrice appliquée à une espèce auxiliaire des cultures : Episyrphus balteatus. L'objectif de la thèse était d'observer la répartition spatiale des individus tandis que nous ferons varier certaines variables d'entrée du modèle (paysage, climat) afin d'étudier les relations entre hétérogénéité des ressources et dynamique de population, le tout en fonction de la stratégie de prospection utilisée par l'espèce. Plus précisément, nous visions trois objectifs: i) déterminer quels facteurs influencent la dynamique de population de l'espèce ; ii) mettre en évidence comment la répartition spatio-temporelle de ces facteurs va favoriser ou non la survie hivernale et iii) replacer ces objectifs théoriques dans le cadre appliqué de la lutte biologique contre les ravageurs de cultures. Dans un premier temps, une approche empirique a permis d'identifier les points clés de la dynamique temporelle de population de l'espèce modèle, en précisant notamment l'importance durant l'hiver des lisières forestières orientées vers le sud. Dans un second temps, le développement du modèle multi-agent HOVER-WINTER a permis de simuler cette dynamique hivernale et de proposer des hypothèses concernant l'utilisation par les individus des prairies et des lisières sud présentes dans le paysage. Enfin, une étude, à l'aide du modèle HOVER-WINTER, de différents scénarios paysagers, d'aménagements potentiels du paysage et de différents modèles de prospection a montré que la configuration du paysage avait un rôle relativement peu important comparé à l'influence de la température et du type de modèle de prospection sur la survie hivernale. Dans tous les cas, les aménagements proposés pour les lisières forestières améliorent la survie hivernale de manière significative

Local and landscape parameters explaining distribution and abundance of Episyrphus balteatus (De Geer, 1776) (Diptera, Syrphidae) in forests and edges of rural landscape

This series of symposia has traditionally been a unique scientific forum for discussions on ecological and behavioral interactions within the guild of insects feeding on aphids. Its focus is to understand how natural control works, with the aim to improve it. After the initial two meetings in Czechoslovakia, symposia were organized in Poland, Hungary, France, Belgium, Canada and Portugal. The ninth meeting was held once again in the Czech Republic. Details on history of the meetings, with bibliographic data from all Proceedings, can be found at http://www.aphidophaga.org

Les paysages boisés sont-ils propices aux syrphidés auxiliaires du blé?

Les éléments semi-naturels des paysages agricoles (bois, haies, bandes enherbées, autres bords de champs) seraient favorables aux insectes auxiliaires des cultures présents naturellement dans les paysages agricoles. Ce « réseau vert » offrirait : i) des abris pour passer l’hiver, ii) des ressources complémentaires et des hôtes de substitution. Dans cette étude, nous avons testé l’hypothèse selon laquelle les syrphes prédateurs des pucerons du blé seraient plus abondants dans des paysages boisés. Ainsi, les pucerons et les syrphes (oeufs, larves, pupes) présents dans les parcelles de blé de deux paysages différant par leur taux de boisement (Boisé : 28%, Peu Boisé : 16%) ont été échantillonnés durant les printemps 2003-2004-2005. De plus, un modèle multi-agent simulant la dynamique hivernale d’une espèce de syrphe (Episyrphus balteatus), a été utilisé sur ces deux paysages. Globalement, les abondances de pucerons et de syrphes prélevés sur le terrain ne diffèrent pas significativement entre les deux paysages. Par contre, les syrphes sont présents plus tôt et sont significativement plus nombreux en paysage boisé. Les simulations de la dynamique hivernale sur le modèle ont montré que les taux de survie hivernale sont plus forts dans les paysages boisés grâce à la présence de prairies et de lisières boisées orientées au Sud. En conclusion, les paysages boisés permettraient une survie plus importante en hiver qui expliquerait des abondances printanières plus fortes. Cet effet disparaîtrait avec l’avancée du printemps. Cette fenêtre temporelle courte (hiver / début du printemps) pourrait être décisive dans la régulation précoce des populations de pucerons

HOVER-WINTER: a multi-agent model to simulate the overwintering of a beneficial insect (Episyrphus balteatus, Diptera, Syrphidae) in a heterogeneous landscape

International audienceUnderstanding how beneficial insects forage in a heterogeneous landscape is of primary importance in conservation biological control. For beneficial insect species that overwinter, survival is linked with the possibility to forage in the landscape for different resources simultaneously. We modelled the behaviour of Episyrphus balteatus (De Geer, 1776), a beneficial species of Syrphidae (Insecta, Diptera) which can overwinter as fertilized adult females and whose larvae feed on aphids occurring on both natural vegetation and crops. The "HOVER-WINTER" multi-agent model focuses on the winter dynamics of an E. balteatus population at the landscape scale. Each individual is modelled as an autonomous agent who behaves according to a set of rules for foraging in the landscape, feeding on flowers, sheltering in forest edges and dying, constrained by climate and land cover. HOVER-WINTER is the first individual based model for E. balteatus. Analysing the trajectories of insects emphasised the role played by meadows and south edges on the overall behaviour of the population. We also studied different scenarios of landscape improvements and showed that landscape configuration had less effect on overwintering success than the temperature and the foraging strategy of the individuals. In any case, landscape improvements greatly enhanced greatly the overwintering success

Modelling the overwintering strategy of a beneficial insect in a heterogeneous landscape using a multi-agent system

International audienceA better knowledge of the foraging ecology of predator insect species that feed on crop pests is of primary importance to improve their beneficial influence for agriculture and for the environment. Multi-agent models are an efficient tool in this respect since they can cope with the complex processes involved in individual behaviour in a heterogeneous space. We applied this method to model the behaviour of Episyrphus balteatus (De Geer, 1776), a helpful species of Syrphidae (Insecta, Diptera) which can overwinter as fertilized adult females and whose larvae feed on aphids occurring on both natural vegetation and crops. The “Hover-Winter” model focuses on the winter dynamics of an E. balteatus population at the landscape scale. Each individual is modelled as an autonomous agent who behaves according to a set of rules for foraging in the landscape, feeding on flowers, sheltering in forest edges and dying, constrained by climate and land cover. The model was developed from data in the literature, expert knowledge and field measurements. This paper presents the structure of the model, the definition of its parameters, the sensitivity of the model to their accuracy and its main outputs. Hover-winter is the first individual based model for E. balteatus and its preliminary results show that it helps to understand how E. balteatus uses agricultural landscapes to survive the winter

Landscape parameters explain the distribution and abundance of Episyrphus balteatus (Diptera, Syrphidae).

International audienceWe studied the importance of forest structure (shape, edge length and orientation) and the crop mosaic (percentage of crops in the total land cover, within 100 and 2000 m from the forests) to the dynamics of an aphidophagous hoverfly Episyrphus balteatus. Adults were collected by Malaise traps located within and on the south- and north-facing edges of 54 forests. In winter, E. balteatus was only found on south-facing edges because of the greater insolation and temperature. In summer, it was more abundant on north-facing edges because of the abundant presence of flowers. In spring, more adults were found on long and south-facing edges than on northern edges. The presence of shrubs within 2000 m also positively affected abundance. In autumn, abundance was positively associated with length of the north-facing edge and forest shape. Emergence traps revealed that in southern France, E. balteatus may overwinter in the larval or puparial stage in forest edges. Overwintering was earlier reported only in adults. Landscape structure, length of forest edges and probably presence of shrub fallows, influence abundance of Episyrphus balteatus

Modelling the biogeomorphologic evolution of vegetated fluvial corridors: the cellular automaton GALET

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Signatures of Life Detected in Images of Rocks Using Neural Network Analysis Demonstrate New Potential for Searching for Biosignatures on the Surface of Mars

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Signatures of Life Detected in Images of Rocks Using Neural Network Analysis Demonstrate New Potential for Searching for Biosignatures on the Surface of Mars.

Microorganisms play a role in the construction or modulation of various types of landforms. They are especially notable for forming microbially induced sedimentary structures (MISS). Such microbial structures have been considered to be among the most likely biosignatures that might be encountered on the martian surface. Twenty-nine algorithms have been tested with images taken during a laboratory experiment for testing their performance in discriminating mat cracks (MISS) from abiotic mud cracks. Among the algorithms, neural network types produced excellent predictions with similar precision of 0.99. Following that step, a convolutional neural network (CNN) approach has been tested to see whether it can conclusively detect MISS in images of rocks and sediment surfaces taken at different natural sites where present and ancient (fossil) microbial mat cracks and abiotic desiccation cracks were observed. The CNN approach showed excellent prediction of biotic and abiotic structures from the images (global precision, sensitivity, and specificity, respectively, 0.99, 0.99, and 0.97). The key areas of interest of the machine matched well with human expertise for distinguishing biotic and abiotic forms (in their geomorphological meaning). The images indicated clear differences between the abiotic and biotic situations expressed at three embedded scales: texture (size, shape, and arrangement of the grains constituting the surface of one form), form (outer shape of one form), and pattern of form arrangement (arrangement of the forms over a few square meters). The most discriminative components for biogenicity were the border of the mat cracks with their tortuous enlarged and blistered morphology more or less curved upward, sometimes with thin laminations. To apply this innovative biogeomorphological approach to the images obtained by rovers on Mars, the main physical and biological sources of variation in abiotic and biotic outcomes must now be further considered