Les effets conjugués de la gestion parcellaire et du contexte paysager et de sa dynamique sur les bioagresseurs et les niveaux de régulation biologique

Ce séminaire est une restitution des principales avancées obtenues dans le cadre des projets ANR PEERLESS «viabilité d’une gestion écologique renforcée de la santé des plantes dans les paysages agricoles » (2013-2017) et FRB SEBIOPAG-PHYTO «déterminants agricoles parcellaires et paysagers des variations de niveaux de régulation biologique » (2014-2017). Le séminaire a rassemblé 60 scientifiques, pour moitié extérieure aux unités INRA partenaires de ces projets. Il s'est déroulé à Paris Paris les 27-28 novembre 2017

Interactions entre végétation des habitats semi-naturels, pratiques agricoles et contrôle biologique des ravageurs des cultures - Optimisation de l'approche bande fleurie

The degradation of semi-natural habitats and land use intensifi cationhave resulted in a loss of ecosystem services. A better understandingof the mechanisms of crop herbivore regulation is neededto improve plant protection and to reduce insecticide treatments.Plant species of semi-natural habitats such as herbaceous fi eldmargins, provide shelter and food resources for crop insects. Thethesis aims to evaluate the role of the fi eld margin vegetation toimprove our knowledge on interaction with crop herbivores and naturalenemies and to optimise ecological engineering approaches.The studies are based on botanical and entomological surveys, onquestionnaire information (land use) and on landscape mapping.In one experiment we manipulated fi eld margin vegetation, to compareeffects of vegetation rich in fl oral resources with control treatments(spontaneous vegetaion, grass strips).We demonstrated theimportance of spontaneous vegetation, particularly the abundanceof fl owering entomophilous plants in regulating crop herbivores.Local factors such as land use intensity and fi eld margin vegetationhad a stronger infl uence on crop herbivores and natural enemiesthan landscape features. A new method of labelling soruce plantnectar with 13C sugar was tested to analyse nectar uptake andthe movements of parasitoids between fi eld margin and crop. Marginvegetation optimised for fl oral resource provisioning improvedregulation service. The results are discussed in terms of managementrecommendations for agri-envrionment schemesLa dégradation des éléments semi-naturels du paysage agricoleet l’intensifi cation des pratiques agricoles ont conduit à l’altérationdes services écosystémiques. Une meilleure compréhensiondes mécanismes de la régulation des bioagresseurs permet ledéveloppement de systèmes agricoles économes en produitsphytosanitaires. Les espèces végétales des habitats semi-naturels,notamment des bordures de parcelles, peuvent constituerdes refuges et proposer des ressources pour les insectes inféodésaux cultures. La thèse vise à expliciter le rôle de la végétationdes bords de champ pour alimenter l’ingénierie agroécologique.Les analyses s’appuient sur des relevés botaniques et entomologiques,sur des enquêtes agronomiques, sur des relevésd’occupation des sols dans le paysage, ainsi que sur la mise enplace de mélanges d’espèces tests le long des cultures.Nous avons mis en évidence l’importance de la végétation spontanéede bordures et surtout du couvert des plantes entomophiles enfl eurs dans la régulation des ravageurs. En comparaison avec lepaysage entourant les parcelles, les facteurs locaux (pratiquesagricoles, fl ore des bordures) ont une plus grande infl uence surles populations des ravageurs. La mise en place d’une nouvelleméthode de marquage du nectar au 13C nous a permis de suivrel’alimentation et le déplacement de parasitoïdes. Les bandesfl euries optimisées pour la production des ressources fl oralesaméliorent la régulation des ravageurs. Les résultats obtenusdans ce travail permettent de formuler de nouvelles pistes degestion de

Interactions between species composition of field margin vegetation, landscape structure, land use and pest control – An optimisation of the wildfl ower strip approach

La dégradation des éléments semi-naturels du paysage agricoleet l’intensifi cation des pratiques agricoles ont conduit à l’altérationdes services écosystémiques. Une meilleure compréhensiondes mécanismes de la régulation des bioagresseurs permet ledéveloppement de systèmes agricoles économes en produitsphytosanitaires. Les espèces végétales des habitats semi-naturels,notamment des bordures de parcelles, peuvent constituerdes refuges et proposer des ressources pour les insectes inféodésaux cultures. La thèse vise à expliciter le rôle de la végétationdes bords de champ pour alimenter l’ingénierie agroécologique.Les analyses s’appuient sur des relevés botaniques et entomologiques,sur des enquêtes agronomiques, sur des relevésd’occupation des sols dans le paysage, ainsi que sur la mise enplace de mélanges d’espèces tests le long des cultures.Nous avons mis en évidence l’importance de la végétation spontanéede bordures et surtout du couvert des plantes entomophiles enfl eurs dans la régulation des ravageurs. En comparaison avec lepaysage entourant les parcelles, les facteurs locaux (pratiquesagricoles, fl ore des bordures) ont une plus grande infl uence surles populations des ravageurs. La mise en place d’une nouvelleméthode de marquage du nectar au 13C nous a permis de suivrel’alimentation et le déplacement de parasitoïdes. Les bandesfl euries optimisées pour la production des ressources fl oralesaméliorent la régulation des ravageurs. Les résultats obtenusdans ce travail permettent de formuler de nouvelles pistes degestion de lThe degradation of semi-natural habitats and land use intensifi cationhave resulted in a loss of ecosystem services. A better understandingof the mechanisms of crop herbivore regulation is neededto improve plant protection and to reduce insecticide treatments.Plant species of semi-natural habitats such as herbaceous fi eldmargins, provide shelter and food resources for crop insects. Thethesis aims to evaluate the role of the fi eld margin vegetation toimprove our knowledge on interaction with crop herbivores and naturalenemies and to optimise ecological engineering approaches.The studies are based on botanical and entomological surveys, onquestionnaire information (land use) and on landscape mapping.In one experiment we manipulated fi eld margin vegetation, to compareeffects of vegetation rich in fl oral resources with control treatments(spontaneous vegetaion, grass strips).We demonstrated theimportance of spontaneous vegetation, particularly the abundanceof fl owering entomophilous plants in regulating crop herbivores.Local factors such as land use intensity and fi eld margin vegetationhad a stronger infl uence on crop herbivores and natural enemiesthan landscape features. A new method of labelling soruce plantnectar with 13C sugar was tested to analyse nectar uptake andthe movements of parasitoids between fi eld margin and crop. Marginvegetation optimised for fl oral resource provisioning improvedregulation service. The results are discussed in terms of managementrecommendations for agri-envrionment scheme

The Protein quality control system manages plant defence compound synthesis

Jasmonates are ubiquitous oxylipin-derived phytohormones that are essential in the regulation of many development, growth and defence processes. Across the plant kingdom, jasmonates act as elicitors of the production of bioactive secondarymetabolites that serve in defence against attackers. Knowledge of the conserved jasmonate perception and early signalling machineries is increasing, but the downstream mechanisms that regulate defence metabolism remain largely unknown. Herewe showthat, in the legumeMedicago truncatula, jasmonate recruits the endoplasmic-reticulum-associated degradation (ERAD)quality control system tomanagethe production of triterpene saponins, widespread bioactive compounds that share a biogenic origin with sterols. An ERAD-type RING membraneanchor E3 ubiquitin ligase is co-expressed with saponin synthesis enzymes to control the activity of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), the rate-limiting enzyme in the supply of the ubiquitous terpene precursor isopentenyl diphosphate. Thus, unrestrained bioactive saponin accumulationis prevented and plant development and integrity secured. This control apparatus is equivalent to the ERAD system that regulates sterol synthesis in yeasts and mammals but that uses distinct E3 ubiquitin ligases, of the HMGR degradation 1 (HRD1) type, to direct destruction of HMGR. Hence, the general principles for the management of sterol and triterpene saponin biosynthesis are conserved across eukaryotes but can be controlled by divergent regulatory cues

Sowing of margin strips rich in floral resources improves herbivore control in adjacent crop fields

International audienceField margin vegetation provides resources for natural enemies of crop herbivores. Thus, the design of plant mixtures improving resource provisioning is being discussed increasingly with respect to improving herbivore control. We set up a field experiment to assess the effect of (i) a wildflower strip optimized for nectar provisioning; (ii) a grass strip and (iii) spontaneous vegetation on herbivore regulation in oilseed rape and wheat. We also analyzed the attractiveness of plant species to natural enemies. The cover of flowering entomophilous plant species as a proxy of floral resource provisioning was twice as high in wildflower strips compared with the other strip treatments. Natural enemy densities were higher within and close to wildflower strips in the field. A corresponding effect on aphid predation and aphid infestation was observed. Significant negative correlations between natural enemy abundance in the margin and aphid infestation in the fields supported a causal relationship. The sown wildflower strip species were more attractive to natural enemies than spontaneous vegetation. The results of the present study demonstrate that improved nectar provisioning increased the predation and parasitism of crop herbivores. Further research on the spatio‐temporal dynamics of interactions is needed to determine why not all crop herbivores respond to an increase of natural enemies in field margins

Effects of spontaneous field margin vegetation on the regulation of herbivores in two winter crops

International audienceNon-crop vegetation of field margins provides resources for natural enemies of crop herbivores. However, it is still not well known whether this resource provisioning effect is strong enough to improve herbivore regulation within crop fields and which plant species and functional groups favour this ecosystem service. A better understanding of the interactions between field margin vegetation and herbivore regulation is crucial to evaluate management strategies and to design suppressive plant mixtures. We surveyed 64 wheat and oilseed rape fields of Western France for two years (16 fields per year and crop) in order (1) to identify plant diversity or group effects on herbivore regulation within crop fields and (2) to identify species within plant groups that improve regulation. Herbivores, herbivore damage and natural enemies were monitored on crop plants at a distance of 5 and 50 m from the field margin. At the same time, the cover and phenological stage of all vascular plants were estimated in the adjacent field margin. The study demonstrated a positive relationship between the cover of entomophilous plant species that were flowering at the survey date and response variables related to herbivore regulation. Plant species richness and the cover of plant species taxonomically close to crop plants had a small influence on herbivores and natural enemies in wheat whereas related wild Brassicaceae increased herbivory and decreased herbivore regulation in oilseed rape. Within the entomophilous flowering plants, several species were significantly related to a better herbivore regulation in univariate analyses. Multivariate ordination techniques allowed the identification of plant species influencing several response variables of herbivore regulation at the same time. Our study demonstrated the importance of entomophilous species that flowered at peak infestation of crop herbivores. Spontaneous field margins rich in flowering entomophilous species provide an important ecosystem service without expensive sowing of seed mixtures

A multi-site experiment to test biocontrol effects of wildflower strips in different French climate zones

International audienceSowing of wildflower strips has been integrated in agri-environment schemes of several European countries. Their beneficial effects on natural enemies of pest insects are well documented but (1) the desired spill-over into crop fields has not always been demonstrated, and (2) the need to adapt sown mixtures to regional climatic differences has been rarely addressed.We set up a multi-site experiment in different French climatic regions to compare effects of a wildflower strip with a grass mixture and spontaneous vegetation. The design included five regions, three to five fields per region and the three strip treatments being repeated in each field. We tested strip treatment effects on vegetation (plant species richness, plant and flower cover) and on natural enemies (hoverflies, ladybirds, aphid predation). In a subset, we further analysed the spill-over into winter wheat fields including natural enemies and pest insects (cereal aphids, leaf beetles).The wildflower strip mixture developed well in all regions and increased plant species richness and flower cover compared with grass strips and spontaneous vegetation. We found a corresponding higher hoverfly abundance and aphid predation in wildflower strips that were consistent in all regions, whereas ladybird abundance was not affected. A significantly higher hoverfly abundance, aphid predation and aphid parasitism in wheat fields close to wildflower strips indicated a spill-over. No corresponding margin treatment effects were observed for aphid and leaf beetle abundance in the field. A multivariate analysis comparing the influence of climate and vegetation parameters showed that floral cover better explained variation in natural enemy abundance and predation than climate. Our results demonstrated that similar mixtures of native plants can be used over large climatic gradients to improve biocontrol. Further research is needed to improve spill-over into crop fields and to obtain consistently strong effects in different climate zones

Effects of spontaneous field margin vegetation and surrounding landscape on Brassica oleracea crop herbivory

International audienceSemi-natural structures of agricultural landscapes are known to provide important habitat functions for natural enemies of crop herbivores. Although several functions such as resource and shelter are related to plant species, the role of the floristic composition is not well understood. Using a correlative approach, we analysed interactions between plant functional groups of spontaneous field margin vegetation and the regulation of crop herbivores. We further compared the influence of the local plant community with that of landscape structure at different scales (50-500 m). We used Brassica oleracea crop plants as phytometers planted into field margins of 48 fields and observed correlations of explanatory variables (vegetation, landscape) and response variables (herbivore and natural enemy abundance, crop damage) for two consecutive years (24 fields x year(-1)). We observed significant positive and negative correlations between plant functional groups and variables related to crop herbivore regulation. In general, plant cover based-models provided a better fit than diversity-based models. Entomophilous flowering plants providing nectar showed a positive correlation to ladybird abundance and aphid parasitism and a negative relationship with major crop plant damage caused by leaf-chewing invertebrates. Cover and diversity of wild Brassicaceae species were positively correlated with flea beetle damage and abundance. Most correlations with plant functional groups remained significant after fitting variables of landscape structure. The density of semi natural habitats showed predominantly positive correlations to crop herbivore regulation, whereas the density of crops was negatively correlated. The number of significant relationships decreased from natural enemy to herbivore abundance and to plant damage. Our results demonstrate the relative importance of field margin vegetation for crop herbivore regulation. The differential responses to plant functional groups support the idea that designing specific plant mixtures may improve biological control. Additional effects of landscape variables suggest that a combination of local and landscape-scale management is the most promising strategy to optimise this ecosystem service. (C) 2016 Elsevier B.V. All rights reserved

The Protein quality control system manages plant defence compound synthesis

Jasmonates are ubiquitous oxylipin-derived phytohormones that are essential in the regulation of many development, growth and defence processes. Across the plant kingdom, jasmonates act as elicitors of the production of bioactive secondarymetabolites that serve in defence against attackers. Knowledge of the conserved jasmonate perception and early signalling machineries is increasing, but the downstream mechanisms that regulate defence metabolism remain largely unknown. Herewe showthat, in the legumeMedicago truncatula, jasmonate recruits the endoplasmic-reticulum-associated degradation (ERAD)quality control system tomanagethe production of triterpene saponins, widespread bioactive compounds that share a biogenic origin with sterols. An ERAD-type RING membraneanchor E3 ubiquitin ligase is co-expressed with saponin synthesis enzymes to control the activity of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), the rate-limiting enzyme in the supply of the ubiquitous terpene precursor isopentenyl diphosphate. Thus, unrestrained bioactive saponin accumulationis prevented and plant development and integrity secured. This control apparatus is equivalent to the ERAD system that regulates sterol synthesis in yeasts and mammals but that uses distinct E3 ubiquitin ligases, of the HMGR degradation 1 (HRD1) type, to direct destruction of HMGR. Hence, the general principles for the management of sterol and triterpene saponin biosynthesis are conserved across eukaryotes but can be controlled by divergent regulatory cues