78 research outputs found
A model-based approach to assess the effectiveness of pest biocontrol by natural enemies
Main goal: The aim of this note is to propose a modeling approach for
assessing the effectiveness of pest biocontrol by natural enemies in
diversified agricultural landscapes including several pesticide-based
management strategies. Our approach combines a stochastic landscape model with
a spatially-explicit model of population dynamics. It enables us to analyze the
effect of the landscape composition (proportion of semi-natural habitat,
non-treated crops, slightly treated crops and conventionally treated crops) on
the effectiveness of pest biocontrol. Effectiveness is measured through
environmental and agronomical descriptors, measuring respectively the impact of
the pesticides on the environment and the average agronomic productivity of the
whole landscape taking into account losses caused by pests.
Conclusions: The effectiveness of the pesticide, the intensity of the
treatment and the pest intrinsic growth rate are found to be the main drivers
of landscape productivity. The loss in productivity due to a reduced use of
pesticide can be partly compensated by biocontrol. However, the model suggests
that it is not possible to maintain a constant level of productivity while
reducing the use of pesticides, even with highly efficient natural enemies.
Fragmentation of the semi-natural habitats and increased crop rotation tend to
slightly enhance the effectiveness of biocontrol but have a marginal effect
compared to the predation rate by natural enemies.
This note was written in the framework of the ANR project PEERLESS
"Predictive Ecological Engineering for Landscape Ecosystem Services and
Sustainability"(ANR-12-AGRO-0006)
Modélisation du mouvement des chevreuils dans un paysage bocager simulé : premiers résultats, projets
Les tiques, dont Ixodes ricinus, espĂšce la plus rĂ©pandue en Europe, sont vecteurs de nombreux agents pathogĂšnes, protozoaires, bactĂ©ries ou virus, qui peuvent ĂȘtre responsables de maladies touchant lâHomme (Borreliose de Lyme) ou lâanimal(babĂ©siose bovine). En vue dâidentifier les zones Ă risque vis-Ă -vis de ces maladies, il est important de connaĂźtre la distribution spatiale des tiques. Cette distribution dĂ©pend dâune part des conditions locales de tempĂ©rature et dâhumiditĂ©, dâautre part des mouvements des hĂŽtes des tiques(Estrada-Peña, 2002). Les chevreuils sont notamment reconnus pour influencer fortement la densitĂ© de tiques(Ruiz-Fons et Gilbert 2010) et se dĂ©placer sur de longues distances. Dans le cadre de lâestimation spatiale des risques, il est nĂ©cessaire de disposer dâun modĂšle de dĂ©placement des hĂŽtes en fonction des caractĂ©ristiques du paysage, dont le dĂ©veloppement nâa pas Ă©tĂ© rĂ©alisĂ© Ă ce jour. Dans un premier temps, une approche thĂ©orique a Ă©tĂ© privilĂ©giĂ©e. Un modĂšle du paysage a Ă©tĂ© dĂ©veloppĂ© via une tesselation de VoronoĂŻ et un processus de marquage. Au sein de ce paysage modĂ©lisĂ©, le mouvement du chevreuil est modĂ©lisĂ© par des Ă©quations diffĂ©rentielles stochastiques. Ce mouvement se dĂ©compose donc en deux termes : un de dĂ©rive, qui dĂ©pend dâune fonction de potentiel reliĂ©e aux diffĂ©rents habitats qui composent le paysage, et un terme de diffusion. A partir dâune premiĂšre fonction potentielle, il est donc possible de simuler le dĂ©placement dâun individu dans un paysage modĂ©lisĂ©. Les dĂ©veloppements actuels visent dans un premier temps Ă tester diffĂ©rentes fonctions de potentiel en fonction de nos connaissances sur le comportement du chevreuil. LâĂ©tape suivante consistera Ă dĂ©velopper des mĂ©thodes dâinfĂ©rence afin dâestimer les paramĂštres Ă partir de donnĂ©es simulĂ©es ou observĂ©es. Par la suite le prototype obtenu pourra ĂȘtre utilisĂ© pour tester lâinfluence des caractĂ©ristiques du paysage sur le mouvement des chevreuils. Enfin, un couplage avec un modĂšle de dynamique de population de tiques (Hoch et al, 2010) fournira des aires de rĂ©partition simulĂ©es des vecteurs
Recommended from our members
Spatially explicit economic effects of non-susceptible pests' invasion on Bt maize
Maize expressing the Bacillus thuringiensis Cry1Ab toxin (Bt maize) provides a more effective control of corn borers
than the use of insecticides. Yet, the spatial expansion of Bt maize may offer ideal ecological conditions for
the development and spread of secondary pests, i.e. pests not susceptible to the expressed toxin. This paper develops
a bio-economic, spatially explicit population model to analyse the spread and economic consequences of
a secondary pest outbreak. Results show that the present use and even an eventual expansion of Bt maize can be
economically and environmentally advantageous as it would decrease insecticide usage intensity. However, we
show that caution is required when considering its widespread use. If a pest outbreak is not identified and dealt
with at an early stage, it could lead to severe economic impacts even if insecticides are used in combination with
the Bt maize. We further discuss potential policy and subsequent management strategies to address this issue
Modélisation et simulation multi-agents de phénomÚnes d'oxydo-réduction (application au complexe III de la chaßne respiratoire)
Les mouvements de larges sous-unités protéiques sont trÚs importants dans la liaison des substrats et les propriétés catalytiques des enzymes. Le but de notre étude a été de combiner la modélisation des réactions d'oxydo-réduction et les changements de conformations des complexes enzymatiques redox afin de décrire la dynamique réactionnelle de ces complexes. Nous avons réutilisé des algorythmes précédemment décrits dans la littérature afin de déterminer les changements conformationnels au sein des complexes redox. Nous avons ensuite développé un SystÚme Multi-Agent permettant la simulation des activités redox de ces complexes. Nous avons appliqué notre approche à l'étude du complexe III de la Chaine Respiratoire Mitochondriale. Notre modÚle nous permet de retrouver le onctionnement normal du complexe III lié à la dynamique de ces réactions redox et de ces mouvements internes.Because movements of large protein structures are key components in ligand docking and enzymatic catalysis, our aim was to combine modeling of the redox reactions and modeling of the conformational changes of enzymatic oxydoreduction complex in order to describe their dynamical functioning. We decided to reused previously described algorithms in order to uncover the conformational changes of redox complexes. We have then developed a Multi-Agent System to simulate the redox activiities of these complexes. We have applied our method to the complex III of the Mitochondrial Respiratory Chain. With this modeling we are able to find the normal functioning of the complex III as a consequence of the reaction mechanisms taking into account the tridimensional structure of the complex and its conformational changes.BORDEAUX2-BU Santé (330632101) / SudocBREST-ENIB (290192307) / SudocSudocFranceF
Favoriser la dynamique d'un auxiliaire de culture Carabidae au sein d'une mosaĂŻque agricole
National audienc
Imagerie pour la quantification de symptÎmes sur feuilles détachées.
National audienceEn pathologie vĂ©gĂ©tale, la quantification de symptĂŽmes est souvent mesurĂ©e de maniĂšre qualitative Ă partir d'Ă©chelles de notation. Afin d'augmenter la prĂ©cision et la fiabilitĂ© des rĂ©sultats nous avons dĂ©cidĂ© de mettre en place une mĂ©thode de quantification par vision numĂ©rique. L'objectif de ce poster est de prĂ©senter les Ă©tapes et les outils nĂ©cessaires Ă la mise en Ćuvre de cette approche
Optimal spatial monitoring of populations described by reactionâdiffusion models
International audienceUsing spatialised population measurements and related geographic habitat data, it is feasible nowadays to derive parsimonious spatially explicit population models and to carry on their parameter estimation. To achieve such goal, reactionâdiffusion models are common in conservation biology and agricultural plant health where they are used, for example, for landscape planning or epidemiological surveillance. Unfortunately, if the mathematical methods and computational power are readily available, biological measurements are not. Despite the high throughput of some habitat related remote sensors, the experimental cost of biological measurements are one of the worst bottleneck against a widespread usage of reactionâdiffusion models. Hence we will recall some classical methods for optimal experimental design that we deem useful to spatial ecologist. Using two case studies, one in landscape ecology and one in conservation biology, we will show how to construct a priori experimental design minimizing variance of parameter estimates, enabling optimal experimental setup under constraints
Automated image processing framework for analysis of the density of fruiting bodies of Leptosphaeria maculans oilseed rape stems
International audienceUnderstanding the transmission of plant pathogen inoculum during the periods when the host plants are not present is crucial for predicting the initiation of epidemics and optimizing mitigation strategies. However, inoculum production at the end of the cropping season, survival during the intercrop period, and the emergence or release of inoculum can be highly variable, difficult to assess, and generally inferred indirectly from symptom data. As a result, a lack of large datasets hampers the study of these epidemiological processes. Here, inoculum production was studied in Leptosphaeria maculans, the cause of phoma stem canker of oilseed rape. The fungus survives on stubble left in the field, from which ascospores are released at the beginning of the next cropping season. An image processing framework was developed to estimate the density of fruiting bodies produced on stem pieces following incubation in field conditions, and a quality assessment of the processing chain was performed. A total of 2540 standardized RGB digital images of stems were then analysed, collected from 27 oilseed rape fields in Brittany over four cropping seasons. Manual post-processing removed 16% of the pictures, e.g. when moisture-induced darkening of the oilseed rape stems caused overestimation of the area covered with fruiting bodies. The potential level of inoculum increased with increasing phoma stem canker severity at harvest, and depended on the source field and the cropping season. This work shows how image-based phenotyping generates high-throughput disease data, opening up the prospect of substantially increased precision in epidemiological studies
- âŠ