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In arable agroecosystems, arthropod communities often have a reduced abundance and diversity, which represents a challenge for sampling techniques needed to detect small differences among these simplified communities. We evaluated the suitability of pitfall traps for comparing the effects of cropping systems on arthropod communities. In a field experiment, we compared the effects of two pitfall trap diameters, the type of preserving fluid and the sampling effort on three metrics (activity density, taxonomic richness, and community weighted mean [CWM] of body size) for carabids and spiders. Trap size affected the observed composition of communities, with large traps yielding a higher proportion of spiders, and a higher richness and CWM body size for both taxa. The type of preserving fluid had a weaker effect. Simulations with various sampling efforts showed that only very different communities could be distinguished with less than 10 traps per field or less than 30 field replicates. Fewer traps were required to find differences between cropping systems for body size than for other metrics. Carabid activity density and body size, and spider genus richness, were the variables better distinguishing between cropping systems with the smallest sampling effort. A high sampling effort was required for comparing activity density and richness across cropping systems. Selection of the most appropriate trap design, metrics, and crops are the main factors for optimizing the trade-off between sampling effort and the ability to detect arthropod community responses to habitat management.

Plant taxonomic and functional diversity promotes interactions at higher trophic levels, but the contribution of functional diversity effects to multitrophic interactions and ecosystem functioning remains unclear. We investigated this relationship in a factorial field experiment comparing the effect of contrasting plant communities on parasitism rates in five herbivore species. We used a mechanistic trait-matching approach between plant and parasitoids to determine the amount of nectar available and accessible to parasitoids. This trait-matching approach best explained the rates of parasitism of each herbivorous species, confirming the predominant role of mass-ratio effects. We found evidence for an effect of functional diversity only in analyses considering the ability of plant communities to support the parasitism of all herbivores simultaneously. Multi-species parasitism was maximal at intermediate levels of functional diversity. Plant specific richness had a negligible influence relative to functional metrics. Plant communities providing large amounts of accessible nectar and with intermediate levels of functional diversity were found to be the most likely to enhance the conservation biological control of diverse crop herbivores.

Winter oilseed rape (OSR) can be grown intercropped with frost-sensitive service plant mixtures. This practice may reduce weed pressure and contribute to providing N for OSR after service plant freezing. However, there is little knowledge of how plants interact together and with the soil in diverse annual crop mixtures. To assess these interactions, two contrasting legume service plants were selected: faba bean and grass pea, as well as a non-legume, the niger plant. OSR and the legumes were then grown in mesocosms alone or intercropped in mixtures of two to four species. The biomass, N contents, N2 fixation, and soil substrate-induced respiration were measured. A single species mostly drove the total dry biomass and the amount of N accumulated by the cover, OSR and faba bean for dry weight and N contents, respectively. Grass pea was highly sensitive to competition with OSR, and its N2 fixation was lower than that of faba bean. The addition of niger did not lead to additional N2 fixation of legumes or total N accumulation and contributed to reducing OSR biomass. The specific composition of the plant mixture did not explain the soil microorganism activity.

Wildflower strips and biodiversity-friendly management are promoted as ways of enhancing biodiversity and natural pest control in agroecosystems. Their efficacy for providing resources and shelters for natural enemies has been well studied, but little is known about how wildflower strip efficacy is mediated by local field management and landscape composition. In this study, we explored the effects of floral resources in perennial flower strips on faba bean aphids and their antagonists in contrasting cropping systems and landscapes. We surveyed 13 faba bean crops in northern France in 2019, and 19 in 2020. We sampled aphids ( Aphis fabae and Acyrthosiphon pisum ) and their antagonists (Syrphidae, Coccinellidae and mummy-forming parasitoids) on three dates during the spring, by visual observation. We assessed the floral resources provided by wildflower strips and spontaneous field margins and collected data on field management practices and land use in the surrounding landscape. We found that the percentage of flowering species in field edges providing accessible nectar to predators had a positive effect on the abundance of Syrphidae and aphid mummies on faba bean plants. The positive effect of nectar resources on Syrphidae and parasitoids decreased with increases in the proportion of semi-natural habitats in the landscape, but no interaction was observed with local management techniques. The temporal dynamics of Aphis fabae and Acyrthosiphon pisum populations were unaffected by their antagonists. The dynamics of A. fabae populations was driven principally by local management practices (i.e. insecticide spraying and tillage). Conversely, the temporal dynamics of A. pisum populations was driven principally by landscape composition (i.e. the proportion of semi-natural habitats and leguminous plants) and was negatively related to insecticide use. Nevertheless, insecticide spraying did not prevent increases in the growth rates of both aphid species, highlighting the need for alternative methods for controlling aphid populations.

Background The pollen beetle, Brassicogethes aeneus (Fabricius, 1775), is one of the most significant pests of oilseed rape. To shed light on past and current pollen beetle demography (dispersal, population size), 12 microsatellite markers were developed, and population genetic diversity and structure were analysed at different spatial scales in France and in Europe from 433 individuals collected in 18 winter oilseed rape fields. Results Genetic differentiation among the population samples was low but was significant between the Estonian sample and the rest of Europe. Isolation by distance was significant only at the European scale. Genetic variability was similar among the 18 population samples. Demographic inferences suggested a recent expansion of B. aeneus population size over Europe, possibly corresponding to an increase in oilseed rape crop area during past decades. Conclusion Current population size and dispersal are not straightforward to estimate from the distribution of genetic variability in B. aeneus over Europe because of the complexity of the demographic history of this pest. Nevertheless, because gene flow was important enough to prevent strong genetic differentiation at large geographical scales, the management of pollen beetle populations should likely be thought of at a continental Europe level. © 2018 Society of Chemical Industry.

International audience; The intercropping of rapeseed with frost-sensitive companion plants (CP) has recently been proposed as a way to mitigate the negative environmental impact of rapeseed crops. Using mixed-effect linear models, we compared the yield and weed amounts of rapeseed intercropped with different CP species with that of rapeseed as a sole crop in an unique dataset of 79 field experiments covering a wide range of climate, soil and practices conditions in the northwestern part of France, from 2009 to 2015. Bayesian model averaging procedure was used to determine the relative contributions of sites characteristics to the effects of intercropping.& para;& para;Before winter, field pea and faba bean had accumulated the largest amounts of dry mass, with more than 100 g m(-2). Rapeseed biomass was reduced by 56% by non-legume CPs and by only 18% by legume CPs, the largest decrease being caused by pea. Non-legumes decreased the nitrogen nutrition index of rapeseed by 7%, whereas pea and faba bean increased this index by 6% and 3%, respectively. Intercropping with non-legume and legume CPs reduced weed amounts by 52% and 38% respectively, with no difference between CP species. Non legume CPs decreased rapeseed yield at harvest by 0.581 ha(-1), whereas faba bean and faba bean + lentil in creased yield by 0.16 and 0.12 t ha(-1) respectively, when fertilized at the recommended rate. Intercropping with faba bean, lentil or a mixture of both made it possible to reduce nitrogen applications by 30-40 kg ha(-1) with no significant decrease in rapeseed yield. Faba bean and faba bean + lentil mixtures had the best overall performance. This work suggests that intercropping rapeseed is promising, particularly in soils with low nitrogen content with an early sowing date in the late summer.

The use of fungicides and insecticides by farmers represents a major threat to biodiversity1, endangering agriculture itself2,3. Landscapes could be designed4to take advantage of the dependencies of pests5,6, pathogens7and their natural enemies8on landscape elements. However, the complexity of the interactions makes it difficult to establish general rules. Despite initial enthusiasm9, the many studies opposing cultivated and semi-natural habitats have not revealed a homogeneous response of pests10and pathogens11to semi-natural habitats. In addition, the question of the impact of crop diversity on pests and pathogens remains largely open12. Based on about half a million observations over nine years on 30 major field crop pests and pathogens spread over all latitudes of metropolitan France, we show that the outbreak risk increases with the area of the host crop in the landscape the previous growing season. The impact on the risk of the host crop area the ongoing growing season diverges between animal pests and pathogens. We also confirm that woodlands, scrublands, hedgerows and grasslands do not have a consistent effect over the spectrum of pests. The spatial and temporal distribution of the resource, the host crop, generally prevails over the effects of potential alternative habitats. Territorial and temporal coordination generally promoting crop diversity but excluding a crop at risk a given year may prove to be key levers for reducing pesticide use14.

International audience; Innovation is central to the strategic orientations of many agronomic research institutes. Little attention has been paid, however, to the links between knowledge production and design processes, defined as processes resulting in the creation of new objects in pursuit of specific goals. Our aim was to analyze the conditions and specificities of the production of scientific knowledge on agro-ecosystems through design processes. Drawing on design theory, we carried out a cross-analysis of nine research projects that included design processes and produced innovative objects (for example blending rules for variety mixtures in low-input crop management routes). These projects were managed by researchers from a range of disciplines (agronomists, geneticists, crop physiologists, and ecologists), and varied in their duration (from three to 15 years) and scale (from plot to landscape). We combined semi-structured interviews with these researchers and the analysis of various documents (scientific papers, PhD theses, technical publications, and research projects or reports). Our findings show that in all case studies, original and general scientific knowledge on agro-ecosystem functioning was produced at various stages throughout the design processes. The originality of this knowledge lies with the new representations that emerged, either of the agro-ecosystem processes at stake, or of farmers' practices. We show that these representations were formed gradually, through successive iterations of both refined formulations of the design target and new knowledge produced, required for its design. Finally, our results highlight the role of confrontation with real-life situations (particularly through agronomic diagnosis or experiments) in the evolution of these representations. Engaging in design processes can thus be seen as a research practice that leads to the production of original knowledge, allowing for a greater diversity of actors' ways of knowing to be taken into account.

International audience; The pollen beetles, Brassicogethes aeneus (Fabricius, 1775), is one of the most significant pests of oilseed rape. To shed light on past and present pollen beetle demography (dispersal, population size), twelve microsatellite markers were developed and population genetic diversity and structure were analyzed at different spatial scales in France and in Europe from 433 individuals collected in 18 winter oilseed rape fields. RESULTS: The genetic differentiation among the population samples was low but significant between the Estonian sample and the rest of Europe. Isolation by distance was only significant at the European scale. The genetic variability was similar among the 18 population samples. Demographic inferences suggested a recent expansion of B. aeneus population size over Europe, possibly corresponding to an increase of oilseed rape crop’s area during the last decades. CONCLUSION: Current population size and dispersal are not straightforward to estimate from the distribution of genetic variability in B. aeneus over Europe because of the complexity of the demographic history of the pests. Nevertheless, as gene flow was important enough to prevent strong genetic differentiation at large geographical scales, the management of pollen beetle populations should likely be thought at the European continental level.

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies., This work was supported through the National Socio-Environmental Synthesis Center (SESYNC) National Science Foundation Award DBI-1052875 for the project “Evidence and Decision-Support Tools for Controlling Agricultural Pests with Conservation Interventions” organized by D.S.K. and R.C.-K

International audience; The role of biodiversity in the delivery of ecosystem services is increasingly being studied by trait-based functional approaches. Here, we review and discuss the contribution of a trait-based approach to understanding plant–arthropod interactions and improving conservation biological control. The stable biological control of multispecies herbivore communities requires functional diversity and a redundancy of natural enemies, including specialists and generalists, with minimal antagonistic interactions. The management of arthropod communities through plant community requires the plant community to perform several functions, including the provision of diversified trophic resources and appropriate physical habitats. Many studies have investigated the ability of plants to provide these functions, but many of the results obtained were limited to single species. The description of communities in terms of traits underlying trophic and non-trophic interactions between plants and animals would make it possible to extrapolate findings to other species. Studies on plant–herbivore and plant–pollinator interactions have identified several traits as important for trophic resource provision, in terms of resource quantity, accessibility, quality and temporal availability. By contrast, traits relating to physical habitat provision and microclimate modification have been little explored. Several metrics describing the functional composition and diversity of communities have been proposed, to extend the trait-based approach to plant community level, but the extent to which multitrophic communities are affected by plant traits remains largely unexplored. The next step will be to identify the combinations of these plant community metrics best explaining their impact on arthropod communities and disentangling the roles of plant functional composition and diversity.

Companion plant intercropping involves growing a cash crop with another plant that is not harvested, to confer a set of benefits on the crop and the environment. Weed control and herbicide use reduction are one of the principal reasons for adopting this approach. Companion plants should compete with weeds for light, nutrients and water, but they may also compete with the crop. The species grown must therefore be carefully chosen and managed so as to outcompete weeds but limit competition with the crop and yield loss. In this meta-analysis, we aimed to quantify the effects of companion plants on weed regulation and cash crop yields, and to analyze their sources of variability. We reviewed different intercropping systems involving an annual cash crop and a legume companion plant from around the world. We report data from 34 scientific articles, corresponding to 476 experimental units (i.e. combinations of site × year × cash crop × legume companion plant species × agricultural practices), and we explore whether intercropping with legume companion plants can control weeds while maintaining crop yield. Yield and weed biomass ratios were analyzed as response variables. We used the type of cash crop (straw cereals, maize or other crops), the methods used to establish the companion plants (living mulch, synchronized sowing or relay intercropping) and the overlap between the growth periods of the companion plants and the cash crop as explanatory variables. Intercropping with a companion plant resulted in a lower weed biomass and a higher yield (win-win situation) than non-weeded or weeded control treatments, in 52% and 36%, respectively, of the experimental units considered. A higher weed biomass associated with a lower yield (lose-lose) was observed in only 13% and 26% of the experimental units, in comparisons with non-weeded and weeded control treatments, respectively. Considering all the experimental units together, the companion plants had no significant effect on cash crop yield, but significantly decreased weed biomass, by 56% relatively to a non-weeded control treatment, and 42% relative to a weeded control treatment. The greatest benefits from companion plant intercropping were reported for maize, with yields 37% higher than those for non-weeded control treatments. The other explanatory variables tested had no significant effect on yield or weed control. Thus, the use of legume companion plants generally seems to enhance weed control without reducing crop yield, but the conditions giving rise to win-win situations should be explored further, to encourage the spread of this technique among farmers.

Many crop pests rely on resources out of crop fields; understanding how they colonize the fields is an important factor to develop integrated pest management. In particular, the time of crop colonization and damage severity might be determined by pest movements between fields and non-crop areas. Notably, the pollen beetle, Brassicogethes aeneus, previously named Meligethes aeneus, one of the most important pests of winter oilseed rape, overwinters in woodlands. As a result, its abundance increases in oilseed rape fields near wooded areas. Here, we assessed the spatio-temporal patterns of the dispersal from woodlands to oilseed rape fields in diversified landscapes of a same region. We observed on four dates the abundance of pollen beetles in 24 fields spread in the Eure department, France. We modeled the abundance as a result of the dispersal from the neighboring woodlands. We compared the modalities of dispersal corresponding to different hypotheses on the dispersal origin, kernel shape and sources of variability. Within oilseed rape the distance to the edges of woodlands is not the main determinant of pollen beetle abundance. On the contrary, the variability of the abundance between fields is largely explained by the dispersal from neighboring woodlands but there is considerable variability between dates, sites and, to a lesser extent, between fields. The two dispersal kernels received similar support from the data and lead to similar conclusions. The mean dispersal distance is 1.2 km but seems to increase from a few hundred meters the first week to more than two kilometers the fourth, allowing the pollen beetles to reach more distant OSR fields. These results suggest that early varieties away from woodlands and late varieties close to the woodlands may limit attacks at the time when oilseed rape is the most sensitive.

Linking spatial pattern and process is a difficult task in landscape ecology because spatial patterns of populations result from complex factors such as individual traits, the spatio-temporal variation of the habitat, and the relationships between the target species and other species. Mechanistic models provide tools to bridge this gap but they are seldom used to study the influence of landscape patterns on biological processes. In this paper, we develop a methodological approach based on sensitivity and multivariate analyses to investigate the relationship between the biological parameters of species and landscape characteristics. As a case study, we used a tritrophic system that includes a host plant (oilseed rape, Brassica napus L.), a pest of the host plant (the pollen beetle, Meligethes aeneus F.), and the main parasitoid of the pest (Tersilochus heterocerus). This tritrophic system was recently represented by a model (Mosaic-Pest) that is spatially explicit at the landscape scale and that includes 32 biological parameters. In the current study, model simulations were compared with observed data from 35 landscapes differing in configuration. Sensitivity analysis using the Morris method identified those biological parameters that were highly sensitive to landscape configuration. Then, multivariate analyses revealed how a parameter's influence on model output could be affected by landscape composition. Comparison of simulated and observed data helped us decrease the uncertainty surrounding the estimated values of the literature-derived parameters describing beetle dispersal and stage transition of the parasitoid at emergence. The advantages of using multivariate sensitivity analyses to disentangle the links between patterns and processes in landscape-scale spatially explicit models are discussed.

Continuous increases in the use of synthetic fertilisers and pesticides in agro-ecosystems have led to an increase in crop production, but also to a simplification of landscape and a decline in biodiversity at the field, cropping system level. Changes at landscape level, such as regional farm specialisation, increases in field size and the removal of hedgerows and woodlots suppression, have strengthened this tendency towards decline. The loss of biodiversity in agro-ecosystems has increased the need for external inputs, as important functions are no longer provided by beneficial species. This has led to an apparently inevitable reliance on petrochemicals in production systems. However, many scientists are arguing that this reliance on pesticides could be considerably reduced by making better use of biotic interactions. This review explores, in the light of recent studies, possible ways to increase beneficial biotic interactions in agro-ecosystems, and to improve bio control pest management at field and landscape scales. This review also points out the possible integrated cropping system on oilseed rape and concludes on the future research that has to be engaged to achieve the goal of improvement the natural bio-control of pests. For example at field scale, it has been shown that the choice of cultivar, the sowing date and nitrogen fertilisation practices can be manipulated to prevent interactions between pests and crop, in either time or space . We have also highlighted that beneficial biotic interactions may result from appropriate changes to the habitats of beneficial species, mediated by soil management and cover or mixing species utilisation. Finally, changes achieved at landscape scale appear promising. However, these approaches frequently also present drawbacks that may not necessarily be outweighed by the beneficial effects. Endly, we propose the approaches to design integrated crop management systems to reduce the damage of pests. However, major research efforts are required to quantify and to use the effects of management practices and to improve our understanding of the interactions between the different levels.

Designing multifunctional landscapes requires accurate indicators to assess the effect of landscape structure on the provision on ecosystem services. Biological pest control relying on natural enemies is an important ecosystem service considered as a sustainable alternative to chemical control. The aim of this study was to measure and compare the accuracy of landscape indicators computed at various spatial scales to predict pollen beetle infestations and successful biological control in northwestern France. The sensitivity, specificity, and probability of correctly ranking fields were estimated for each indicator based on a survey of 42 fields using the receiver operating characteristic procedure. For pest infestation, the proportion of woodland and the proportion of semi-natural habitats were found to be informative indicators with good discriminatory abilities. For biological control, the proportion of woodland, the proportion of semi-natural habitats and the proportion of the previous year's oilseed rape fields with reduced soil tillage were found to be informative indicators with good discriminatory abilities. By using indicator values and optimal thresholds we were able to compute maps of areas at risk for pest infestation and those displaying successful biological control at the regional scale. This study provides tools that could help extension services, landscape planners, and policy makers in optimizing landscape structure according to the provision of a key ecosystem service. The results of this study also provide new grounds for understanding trophic interactions at the regional scale as well as the ambivalent effect of landscape complexity on pest and natural enemy populations.

The development of integrated pest management strategies requires that the semi-natural habitats scattered across the landscape are taken into account. Particular determinants of insect pest abundance in overwintering habitats just before they migrate onto crops appear to be poorly known and of crucial importance for understanding patterns of crop colonization and pest population dynamics at the landscape scale. The emergence of pollen beetle Meligethes aeneus F. was studied in grassland, woodland edge and woodland interior over a 3-year survey in France using macro-emergence traps. A suite of variables at the local and the landscape scale was assessed for each trap, aiming to identify potential relevant habitat indicators. The effects of habitat characteristics were evaluated using partial least square regressions. It was found that M. aeneus can overwinter in all types of habitat but that particular habitat characteristics at the local and landscape scales may explain their abundance in overwintering sites more than the types of habitat: relative altitude, litter thickness, soil moisture and proximity to the previous year's oilseed rape fields appear to be positively correlated with abundance of adults over the 3 years. Hence, the abundance of emerged pollen beetles depends on both the landscape configuration of the previous year's oilseed rape fields around overwintering sites and local habitat characteristics. Landscape configuration may determine population flow towards overwintering sites in the late summer, and local habitat characteristics may influence survival rates during the winter. The findings of the present study provide valuable insight into the role of semi-natural habitats as a source of pests, patterns of crop colonization in the spring, and the influence of landscape on pollen beetle abundance.

In organic farming, weeds are one of the threats that limit crop yield. An early prediction of weed effect on yield loss and the size of late weed populations could help farmers and advisors to improve weed management. Numerous studies predicting the effect of weeds on yield have already been conducted, but the level of uncertainty about weed effect is expected to be very high in organic crops. It is thus more appropriate to provide farmers and advisors with distributions of possible production levels, rather than with point values. The purpose of this study was to estimate the effect of early weed density at the end of the tillering stage of organic winter wheat on subsequent yield and on late weed density at flowering, by using quantile regression. Results showed that this method can be applied to a hyperbolic model and to an allometric density-dependent model, to describe the distribution of yield values and of late weed density respectively, as functions of early weed density measurements. Mechanical weed control showed no significant effect on the relationship between early weed density and grain yield, but it decreased late weed density. Yield and late weed density distributions derived by quantile regression provided sound information on the possible effect of weeds on organic winter wheat production.

The use of legume cover crops as green manure is often seen as an effective means of supplying nitrogen to the following crop. As winter oilseed rape requires a large amount of N in the spring, the introduction of frost-sensitive legume living mulch (killed off during the winter) is a promising way of decreasing mineral N fertiliser inputs. The aim of this study was to assess the supply of biological N to rape during the spring from several frost-sensitive legumes, grown as intercropped living mulches. We carried out a field trial over two growing seasons before sowing, comparing seven legume species and three legume mixtures intercropped with rape, and two levels of soil mineral N. The presence of legumes, living during the autumn and dead during the spring, resulted in 20-40 kgN ha(-1) more nitrogen uptake in oilseed rape, by the end of flowering, compared to rape grown as a sole crop. Moreover, the use of N-15-labelled nitrogen fertiliser showed that this increase in rape N accumulation was due to the mineralisation of legume residues, but also to other mechanisms such as increase in fertiliser-N recovery and in soil organic matter mineralisation. (C) 2016 Elsevier B.V. All rights reserved.

Many organic farmers hesitate to grow winter oilseed rape (WOSR), despite its usefulness for crop rotations and animal fodder, because it is attacked by many insects, which are difficult to control without chemical treatments. In a geographically broad network of farmer’s fields, we analysed the effect of various crop management factors and of the surrounding field environment on a large range of insects known to damage WOSR: root maggot (Delia radicum L.), cabbage stem flea beetle (Psylliodes chrysocephala L.), rape stem weevil (Ceuthorhynchus napi Gyl) and pollen beetle (Meligethes aeneus F.). Our results confirm the effect of sowing date, plant density and soil tillage regime on root maggot attacks and cabbage stem flea beetle larva infestation. Early sowing tended to increase root maggot damage whereas it was associated with a lower level of attack of cabbage stem flea beetle. High plant density tended to decrease the damage or the attack of all insects. We show that nitrogen availability in the soil affect cabbage stem flea beetle, stem weevil levels and pollen beetle damage: the negative effect of soil nitrogen content on pollen beetle damage may be related to the significant effect of nitrogen on plant vigour and, therefore, to the compensation of pollen beetle damage on new racemes. If all insects were considered together, the proportion of land under WOSR in the region and the surrounding environment had a significant effect on pest occurrence. In regions with a high proportion of land under WOSR, the proportion of plants attacked by root maggot and pollen beetle tended to increase. Conversely, regions with high proportions of land under WOSR tended to have a smaller proportion of plants with cabbage stem flea beetle larvae or damage, whatever the environment surrounding the field. For almost all the pests considered, the fields displaying the most severe pest attacks in regions with more than 1.2% WOSR were bounded by trees, hedges and bushes. Conversely, in regions with a lower percentage of land under WOSR, woodland around the field reduced the occurrence of pest attacks

Nitrogen management is complex in oilseed-rape for several reasons: the crop can uptake high amounts of nitrogen during autumn, but a part of this nitrogen is lost through leaves fall during winter and spring, event if these fallen leaves are mineralized and contribute partly to the crop nitrogen nutrition. Moreover, recent results have shown that some periods of N deficiency during the crop cycle are not detrimental for yield. Finally, higher seed oil content are obtained with lower nitrogen fertilisation. All these results suggest that a sub-optimal nitrogen nutrition of the crop could lead to high yields and high seed quality, with low losses through environment. In order to design such fertilisation strategies, the use of a crop model, simulating the variables determinant in the yield and grain quality formation and their interaction with environment, can help advisors. As numerous results on the yield and quality determinants of a rape crop have been obtained in the recent years, the available Azodyn-wheat model has been adapted to the specificities of this crop, based on this knowledge. This paper aims at describing the main results on yield and quality elaboration of a rape crop, and then the designing of the Azodyn-rape model. Then, some results of the model evaluation are given and uses of the model for nitrogen fertilisation management are proposed.

Living mulches are generally seen as a possible way to decrease the reliance on pesticides. We investigated the effect of a frost-sensitive legume living mulch on weed control during the autumn and cash crop performance, in winter oilseed rape crops. A field trial was carried out over two years, comparing seven legume species—fenugreek, spring faba bean, grass pea, lentil, field pea, berseem clover and spring common vetch—and three legume mixtures, as living mulches, in crops with two levels of soil mineral nitrogen content before sowing. The presence of the legume living mulch decreased weed abundance before winter. Field pea, berseem clover, common vetch and the common vetch/faba bean/berseem clover mixture were particularly effective, regardless of the growing conditions, decreasing weed abundance by 20–75% with respect to that in the crop grown alone, in the absence of herbicide application. Weed abundance before winter was negatively correlated with total intercrop biomass, and this relationship was dependent on the legume species considered and soil mineral nitrogen content. As with other legume intercrops, the level of soil mineral nitrogen had a strong influence on intercrop structure, modifying the proportion of legume biomass produced. The legume/oilseed rape biomass ratio was also found to be a useful indicator in all growing conditions: the higher the ratio, the more efficient the weed control. However, a high ratio was associated with a higher risk of competition with the cash crop. The choice of the most appropriate legume living mulch is therefore a compromise between the anticipated ecosystem services and the potential disservices provided by the legume mulch. The introduction of a legume living mulch did not entirely prevent weed growth, but was clearly a relevant agroecological solution for decreasing herbicide, while increasing the sustainability and diversity of weed-control strategies in cropping systems.

Mixing plant species in agroecosystems is highlighted as an agroecological solution to reduce pesticides and fertilizers while maintaining profitability. In the French context, intercropping frost-sensitive legume crops with winter oilseed rape is potentially interesting and began to be implemented by farmers. In this study we aimed at measuring the services and disservices of this intercrop with three different legume mixtures, in terms of growth and yield for rapeseed, ground cover of weeds in autumn and damage caused by rape winter stem weevil. The experiment was carried out at four sites from 2011 to 2014. We showed higher total aerial dry weights and total aerial nitrogen contents in the intercrops compared to sole winter oilseed rape in November. The companion plants contributed to the control of weeds and the mitigation of rape winter stem weevil damage, notably through the increase in the total aerial weight. In spring, after destruction of the companion plants, the intercrops had partially compensated a reduction in the N fertilization rate (–30 kg per hectare) in terms of aerial nitrogen content in rapeseed, with no consequences on the yield which was maintained or even increased. There were probably other interactions such as an improvement in rapeseed root exploration. The consequences were an increase in the nitrogen use efficiency in intercrops. The intercrop with faba bean and lentil showed the best results in terms of autumn growth, weed control, reduction in rape winter stem weevil damage, and rapeseed N content in spring and yield. Intercropping frost-sensitive legume crops with winter oilseed rape is thus a promising way to reconcile yield and reduction in pesticides and fertilizer use and perhaps to benefit more widely to the cropping system.

International audience; Many laboratory studies have demonstrated that parasitoids of various species depend on sugar sources such as nectar or honeydew. However, studies about nectar acquisition by parasitoids foraging in the field are scarce. Tersilochus heterocerus Thomson is one of the more abundant and widespread parasitoids of the pollen beetle (Meligethes aeneus F.) but nothing is known about the nutritional ecology of this species. In this study we examined the nutritional state of T. heterocerus at the time of emergence and at various time periods throughout the season while foraging in the field using high-performance anion-exchange chromatography. We found that: (i) T. heterocerus emerge with relatively small amounts of sugar, composed mainly of trehalose, glucose and fructose; (ii) the first parasitoids caught just after they appeared in the field at the beginning of oilseed rape flowering had already consumed significant amounts of sugar reserves; and (iii) the total amount of sugar at the end of flowering was always significantly higher than the total amount of sugar at the beginning of flowering. This study provides valuable insights into the acquisition of sugar in the field by the parasitoid T. heterocerus and suggests that nectar acquisition takes place in the oilseed rape field or in the surrounding landscape.

In landscape ecology, correlational approaches are typically used to analyse links between local population abundance, and the surrounding habitat amount to estimate biologically-relevant landscape size (extent) for managing endangered or pest populations. The direction, strength, and spatial extent of the correlations are then sometimes interpreted in terms of species population parameters. Here we simulated the population dynamics of generalized species across spatially explicit landscapes that included two distinct habitat types. We investigated how characteristics of a landscape (structure), including the variation in habitat quality and spatial aggregation of the habitat, and the precise population-dynamic properties of the simulated species (dispersal and growth rates) affect the correlation between population abundance and amount of surrounding favourable habitat in the landscape. To evaluate these spatial extents of correlation, proportions of favourable habitat were calculated within several circles of increasing diameter centred on sampling patches of favourable habitat where population abundance was recorded. We found that the value of the correlation coefficients between population abundance and amount of surrounding favourable habitat depended on both population dynamic parameters and landscape characteristics. Coefficients of correlation increased with the variation in habitat quality and the aggregation of favourable habitat in the landscape, but decreased with the dispersal distance. The distance at which the correlation was maximized was sensitive to an interaction between the level of aggregation of the habitat and the dispersal distance; whereas the greatest distance at which a significant correlation occurred was more sensitive to the variation in habitat quality. Our results corroborate the view that correlational analyses do provide information on the local population dynamics of a species in a given habitat type and on its dispersal rate parameters. However, even in simplified, model frameworks, direct relationships are often difficult to disentangle and global landscape characteristics should be reported in any studies intended to derive population-dynamic parameters from correlations. Where possible, replicated landscapes should be examined in order to control for the interaction between population dynamics and landscape structure. Finally, we recommend using species-specific, population-dynamic modelling in order to interpret correctly the observed patterns of correlation in the landscape.

Understanding the determinants of insect–plant interactions and pest population dynamics at multiple spatial scales is a pre-requisite for developing innovative crop protection strategies and increasing the sustainability of agroecosystems. In a two-year study, we investigated the relative influence of local crop management and landscape context on pollen beetle (Meligethes spp.) abundance and damage at 8 different spatial scales around 42 oilseed rape fields using a multi-model inference approach. We found that pest abundance was mainly determined by the proportion of grassland and woodland in the landscape at scales ranging from 1500 m to 2000 m. Pollen beetle damage was affected both by local management and landscape predictors at scales ranging from 1500 m to 2000 m. Indeed, damage was negatively correlated with the nitrogen nutrition index of the plants and positively correlated with the proportion of woodland in the landscape at a large scale. Our multi-scale approach revealed that landscape complexity determines pollen beetle abundance in the spring and that nitrogen nutrition of the plants influences crop ability to compensate bud abortions resulting from pest attacks. The results are discussed in relation to crop management, pest dispersal ability and landscape structure.

Concerns about the adverse impacts of pesticides on the environment and their inevitable negative side-effects on non-target organisms have been growing since the 1960’s. In western Europe, Winter Oilseed Rape (Brassica napus L. WOSR) has to cope with numerous damaging insects (Alford et al., 2003 and Williams et al., 2010), and other diseases and weeds. In conventional farming, as a consequence, an important and increasing use of pesticides is observed in the major french production areas (Ecophyto RD Dejoux et al.,2003) are also well known.

The intensification of agriculture has led to a loss of biodiversity and subsequently to a decrease in ecosystem services, including regulation of pests by natural enemies. Biological regulation of pests is a complex process affected by both landscape configuration and agricultural practices. Although modeling tools are needed to design innovative integrated pest management strategies that consider tritrophic interactions at the landscape scale, landscape models that consider agricultural practices as levers to enhance biological regulation are lacking. To begin filling this gap, we developed a grid-based lattice model called Mosaic-Pest that simulates the spatio-temporal dynamics of Meligethes aeneus, a major pest of oilseed rape, and its parasitoid, Tersilochus heterocerus through a landscape that changes through time according to agricultural practices. The following agricultural practices were assumed to influence the tritrophic system and were included in the model: crop allocation in time and space, ploughing, and trap crop planting. To test the effect of agricultural practices on biological regulation across landscape configurations, we used a complete factorial design with the variables described below and ran long-term simulations using Mosaic-Pest. The model showed that crop rotation and the use of trap crop greatly affected pollen beetle densities and parasitism rates while ploughing had only a small effect. The use of Mosaic-Pest as a tool to select the combination of agricultural practices that best limit the pest population is discussed.

Improving our understanding about how natural enemies respond to semi-natural habitats and crop management scattered in the landscape may contribute to the development of ecologically based pest management strategies maximising biological control services. We investigated how soil tillage and semi-natural habitats influenced the parasitism rates of pollen beetle (Meligethes aeneus F.) larvae at 8 different spatial scales (from 250 to 2000 m radius circular sectors) in 42 oilseed rape (OSR) fields. We used multimodel inference approaches to identify and rank the influence of soil tillage and semi-natural habitats on parasitism rates, and to quantify the importance of each scale. Parasitism rates were due to three univoltine parasitoid species (Tersilochus heterocerus, Phradis morionellus and P. interstitialis) and varied from 0 to 98%. We found that both fine and large scales contributed to explain significantly parasitism rates, indicating that biological control of pollen beetle is a multi-scale process. At the 250 m scale, parasitism rates of T. heterocerus were positively related to the proportion of semi-natural habitats and the proximity to previous year OSR fields. At large scales (1500 to 2000 m), parasitism rates of T. heterocerus were positively related to semi-natural habitats and negatively related to the proportion of previous year OSR fields with conventional soil tillage. Parasitism rates of Phradis spp. were only positively related to the proportion of semi-natural habitats at the 1250 and 1500 m scales. These multi-scale effects are discussed in relation to the influence of semi-natural habitats and soil tillage on parasitoid populations and their movement behaviours within the landscape.

The development of sustainable cropping systems is a major challenge for agronomists and crop scientists in many regions of the world. The prophylactic uses of broad spectrum insecticides are actually the main solution for farmers to control insect pests. Therefore, there is a growing need to develop innovative crop protection strategies through an integrated approach which aims at favouring natural enemies and enhancing biological control in agroecosystems. The development of such strategies requires a thorough understanding of agroecosystem functioning. In this chapter, we present the effects of different elements, from the field scale to the landscape scale that are known to enhance biological control in agroecosystems and limit pest damage with particular reference to oilseed rape. Linking integrated pest management and landscape ecology brings a regional perspective to the management of pest populations. Available techniques are often added together rather than combined in an integrated way and are rarely evaluated through environmental and economical criteria. Therefore, we present a methodological framework to design and assess sustainable cropping systems, with a particular emphasis on complementariness between models, systemic trials and more analytical approaches. Implementation of sustainable cropping systems implies the development of new integrated pest management strategies and thereby an increased participation of the different stakeholders from farmers to policy makers.

There is a growing body of evidence to suggest that the simplification of land uses associated with a strong dependence on agrochemical inputs is decreasing environmental quality, threatening biodiversity, and increasing the likelihood of pest outbreaks. The development of farming systems with greater reliance on ecosystem services, such as biological control of insect pests, should increase the sustainability of agroecosystems. However, the factors responsible for the maintenance or enhancement of natural pest control remain unclear. The goal of this review is, therefore, to expose which elements, from the field to the landscape scale, influence natural enemy populations and pest regulation. We present here the principal effects of seminatural habitats, farming systems, and crop management on the abundance of insect pests and their biological control, with a view to evaluating their relative importance and identifying key elements that regulate natural pest control interactions. Because of the range of spatial and temporal scales experienced by these organisms, we advocate, in studies investigating trophic relations and biological pest control, a clear description of cropping systems and an explicit consideration of seminatural habitats and more generally of the surrounding landscape. Through this review, we also indicate gaps in knowledge and demonstrate the interest of linking agronomy and landscape ecology to understand trophic interactions, maximize natural pest control, and limit pesticide applications. Quantifying the relative importance of both local and landscape scales is a fundamental step in the design and assessment of ecologically sound integrated pest management strategies for farmers.

Correspondance: malezieux@cirad.fr; International audience; The evolution of natural ecosystems is controled by a high level of biodiversity, In sharp contrast, intensive agricultural systems involve monocultures associated with high input of chemical fertilisers and pesticides. Intensive agricultural systems have clearly negative impacts on soil and water quality and on biodiversity conservation. Alternatively, cropping systems based on carefully designed species mixtures reveal many potential advantages under various conditions, both in temperate and tropical agriculture. This article reviews those potential advantages by addressing the reasons for mixing plant species; the concepts and tools required for understanding and designing cropping systems with mixed species; and the ways of simulating multispecies cropping systems with models. Multispecies systems are diverse and may include annual and perennial crops on a gradient of complexity from 2 to n species. A literature survey shows potential advantages such as (1) higher overall productivity, (2) better control of pests and diseases, (3) enhanced ecological services and (4) greater economic profitability. Agronomic and ecological conceptual frameworks are examined for a clearer understanding of cropping systems, including the concepts of competition and facilitation, above- and belowground interactions and the types of biological interactions between species that enable better pest management in the system. After a review of existing models, future directions in modelling plant mixtures are proposed. We conclude on the need to enhance agricultural research on these multispecies systems, combining both agronomic and ecological concepts and tools.

International audience; Organic agriculture could achieve the objectives of sustainable agriculture by banning the use of synthetic fertilizers and pesticides. However, organic crops generally show lower performances than conventional ones. In France, organic winter wheat production is characterized by low grain protein content. There is a crucial need for better understanding the variability of grain protein content, because millers require batches with values over 10.5% of dry matter. Here, a regional agronomic diagnosis was carried out to identify the limiting factors and crop management practices explaining the variability of grain protein content. The studied field network was a set of 51 organic winter wheat plots in south-eastern France. The mixed-model method was used for identifying and ranking the limiting factors and the crop management practices responsible for variation in limiting factors. Our results show that the grain protein content variation was mostly explained by the baking quality grade of the cultivar, crop nitrogen status and weed density at flowering. There was a positive correlation between grain protein content and both crop nitrogen status and weed density. To a lesser extent, climatic factors also explained grain protein content variability. A lower water stress increased grain protein content, whereas an increase in the photothermal quotient and daily temperature over 25 °C reduced grain protein content. In south-eastern France, grain protein content of organic winter wheat could be increased by improving fertilization management, using an improved baking quality grade cultivar, choosing a legume fodder crop as preceding crop, or by avoiding late sowing dates.

International audience; The development of sustainable cropping systems is a key priority for agronomists and crop scientists. A first step involves understanding the relationship between cropping system performance and farmers’ practices. To complete this step, a methodological framework entitled Regional Agronomic Diagnosis (RAD) has been developed. During the last ten years, the scope of the regional agronomic diagnosis has been enlarged to include several factors describing crop quality and the environmental impact of cropping systems. Regional agronomic diagnosis has led to several major advances such as (1) the assessment of the effect of preceding crop and soil structure on malting barley quality in France and (2) the assessment of the effects of ploughing, nematicide use and fertilisers on soil properties in intensive banana plantations in the West Indies. Improvements have also been gained in methodology, particularly by the selection of indicators for assessing the effects of crop management, soil and weather conditions, and data analysis. Finally, regional agronomic diagnosis has been integrated into more general approaches of agricultural development. We review here this methodological progress.

The yield of organic winter oilseed rape (WOSR) crop is low and variable in organic farming, but the reasons responsible for this problem are not clear. Aiming to identify the factors affecting organic oilseed rape yields, we carried out a diagnostic study on a network of 19 farmers’ fields in four contrasting regions of France over a two-year period. Weed density and biomass, nitrogen absorption by the crop and by weeds, and nutrient availability in the soil, as well as the occurrence of pests and diseases, were assessed at four developmental stages. A range of possible limiting factors throughout the crop cycle led us to use a regression procedure for different periods, using the yield components during spring and biomass during autumn as dependent variables. We identified factors limiting yield and the critical time points at which they acted, which has never been done. Yield variation was strongly correlated with number of grains.m−2. Dry biomass of weeds, nitrogen uptake by weeds and density of weeds appeared to explain 39% of variation in crop biomass in early winter, while pollen beetle and rape stem weevil damage explained 4.5% and 12% of variation in the number of flowers.m−2 and the number of branches.m−2, respectively. Crop nitrogen deficiencies occurring before branching were strongly correlated with weed biomass in flowering. Analysis of covariance showed that sowing date, soil management and the quantity of organic manure application may have significantly affected the nitrogen nutrition index, nitrogen uptake by plants and ratio of weed biomass: a late sowing date and shallow soil tillage were related to a low crop nitrogen nutrition index and high ratio of weed biomass. From a practical point of view, this study demonstrated that it should be possible to reduce weed competition by ensuring that the amount of nitrogen in soil before sowing is around 100 kg/ha.

International audience; Chemical weed control before crop and weed emergence is a systematic practice in winter oilseed rape crops in France. It would be profitable both for farmers and the environment to predict the level of weed infestation early on in the growing season and to control weeds only when necessary using post-emergence weed control. The objective of this paper was to develop and evaluate simple models to predict weed biomass in oilseed rape crops. The model input variables were related to weed population characteristics and farmers' practices. The models can be used to classify oilseed rape plots into two categories: plots with a level of weed infestation above a threshold or those with level of weed infestation below a threshold. A data set including 3 years of experiments, conducted across several regions in France, was used to estimate the parameters and to evaluate the models. High values of sensitivity and specificity were obtained when weed biomass was predicted as a function of sowing date, type of soil tillage, soil mineral nitrogen, crop density, weed density at emergence, and main characteristics of the most abundant weed species. Model performance strongly decreased when input variables related to the weed population were not taken into account. The best models correctly classified 90% of the plots with high weed infestation and 64% of the plots with low weed infestation.