Publications directement issues du projet

• Connectivity of cropped vs. semi-natural habitats mediates biodiversity: A case study of carabid beetles communities

Green-veining policies aiming at restoring biodiversity in agricultural landscapes mainly focus on the connectivity of semi-natural habitats. However, little is known about the potential role of crop connectivity for the biodiversity using cropped habitats. The goal of the present study was to investigate the effects of habitat connectivity related to annual crops vs. semi-natural habitats (woody elements) on insect biodiversity (carabid beetles) in agricultural landscapes, considering contrasted groups of species in terms of habitat preference and dispersal ability. Results showed that the spatial configuration and connectivity of annual crops in the landscape (here, up to 500 m) can contribute to increased abundance of some groups of carabid species. Spatial continuities between spring and winter crops (in 250 m radius circles) had beneficial effects on farmland species with low mobility (brachypterous) in maize crops, possibly reflecting resource complementation processes. The connectivity of annual crops also had positive effects on abundances of dimorphic farmland species in maize crops and of forest species in woodland, but at contrasted spatial scales (in 250 m vs. 50 m radius circles respectively). The present study also revealed antagonistic effects of landscape patterns related to both crops (edge length between winter and spring crops) and semi-natural habitats (percent cover of woodland) on farmland and forest species, highlighting critical issues regarding the conservation of such contrasted ecological species groups in agricultural landscapes

Aviron, S., Lalechère, E., Duflot, R., Parisey, N., Poggi, S. (2018). Connectivity of cropped vs. semi-natural habitats mediates biodiversity: A case study of carabid beetles communities. Agriculture, Ecosystems & Environment 268, 34-43. DOI

• L'hétérogénéité du paysage local affecte la colonisation par les auxiliaires des cultures sous abri

Conservation biological control of crop pests is considered a promising strategy in protected horticultural cropping systems. In Mediterranean regions, crop colonization by native predatory mirid bugs is frequent but highly heterogeneous among crop production sites. The contribution of landscape heterogeneity to the variability in colonization levels remains little explored, although it is a major driver of the abundance of natural enemies of pests in open field cropping systems. The goal of our study was to assess whether landscape heterogeneity (land-cover diversity, percent cover, and spatial configuration) at a local scale (up to 300 m) affects colonization of protected crops by Macrolophus and Dicyphus mirids, and whether these effects are significantly greater or lower than those of crop management practices. In southern France (Roussillon) in 2010 and 2011, we collected data on mirid populations, pest infestation levels, crop management practices, and landscape heterogeneity within 300 m buffers. We investigated relationships between natural enemies, farming practices, and landscape metrics using an algorithm for random forests combined with GLM analyses. Tomato crops were colonized the most by Macrolophus mirids in landscapes with fallow, suggesting that these semi-natural habitats contribute to mirid movements between protected crops and the surrounding landscape. In contrast, crop colonization by mirids was reduced by nearby orchard, which reflected either sink effects due to intensive management practices or dilution effects linked to herbaceous resources. Landscape composition and configuration had similar effects on mirid populations. Macrolophus and Dicyphus mirids responded the most to lanscape heterogeneity at different spatial scales (200–300 and 100m scales, respectively), possibly reflecting different dispersal abilities. However, effects of landscape heterogeneity on mirids were lower than those of crop management practices. Our study suggests that maintaining large areas of semi-natural habitats with ruderal vegetation typical of fallow is important to ensure colonization of protected crops by natural enemies of pests. Our findings emphasize that converting farms from conventional to organic production systems and adopting integrated plant management practices remain the most promising strategies to enhance populations of natural enemies in protected horticultural crops in Mediterranean regions.

Aviron, S., Poggi, S., Varennes, Y-D., Lefèvre, A. (2016). Local Landscape Heterogeneity Affects Crop Colonization by Natural Enemies of Pests in Protected Horticultural Cropping Systems. Agriculture, Ecosystems & Environment 227, 1-10. DOI 

• MAPI, un nouvel outil pour explorer et visualiser les structures spatiales à partir de mesures pairées

1. Visualisation of spatial networks based on pairwise metrics such as (dis)similarity coefficients provides direct information on spatial organisation of biological systems. However, for large networks, graphical representations are often unreadable as nodes (samples), and edges (links between samples) strongly overlap. We present a new method, MAPI, allowing translation from spatial networks to variation surfaces.

2. MAPI relies on (i) a spatial network in which samples are linked by ellipses and (ii) a grid of hexagonal cells encompassing the study area. Pairwise metric values are attributed to ellipses and averaged within the cells they intersect. The resulting surface of variation can be displayed as a colour map in Geographical Information System (GIS), along with other relevant layers, such as land cover. The method also allows the identification of significant discontinuities in grid cell values through a nonparametric randomisation procedure.

3. The interest of MAPI is here demonstrated in the field of spatial and landscape genetics. Using simulated test data sets, as well as observed data from three biological models, we show that MAPI is (i) relatively insensitive to confounding effects resulting from isolation by distance (i.e. over-structuring), (ii) efficient in detecting barriers when they are not too permeable to gene flow and, (iii) useful to explore relationships between spatial genetic patterns and landscape features.

4. MAPI is freely provided as a PostgreSQL/PostGIS data base extension allowing easy interaction with GIS or the r software and other programming languages. Although developed for spatial and landscape genetics, the method can also be useful to visualise spatial organisation from other kinds of data from which pairwise metrics can be computed.

Piry, S., Chapuis, M-P., Gauffre, B., Papaïx, J., Cruaud, A., Berthier, K. (2016). Mapping Averaged Pairwise Information (MAPI): a new exploratory tool to uncover spatial structure. Methods in Ecology and Evolution. DOI

• L'impact de la composition du paysage sur l'abondance de l'araignée Cheiracanthium mildei en verger dépend de la gestion de ces vergers

Enhancing naturally occurring generalist predators can improve pest control. In orchards, canopy-dwelling species are major actors of pest control because pests attack fruits and growing shoots within the canopy. Cheiracanthium mildei, an arboreal spider, is a predator of several important insect pests. We assessed its autumnal occurrence in a set of 61 commercial apple orchards over three consecutive years (2010–2012). We determined the impact of agronomic and land-cover characteristics on C. mildei occurrence at both the local and landscape levels using a random forest analysis and regression trees. This approach highlighted the differential effect of landscape variables according to local orchard pest management. First, the presence of exclusion nets against the codling moth (Cydia pomonella) increased C. mildei occurrence by 59%. Second, landscape variables only influenced C. mildei occurrence in orchards that were not covered by nets. In particular, abandoned orchards increased C. mildei occurrence in orchards not covered by nets and not surrounded by organic orchards. Third, overall, habitats containing trees increased C. mildei abundance in orchards with and without nets, which is consistent with the arboreal habitat of this species. Lastly, the occurrences of C. mildei and of C. pomonella were not related, indicating that the enhancement of C. mildei does not preclude a control of this major pest.

Lefebvre, M., Franck, P., Toubon, J.-F., Bouvier, J.-C., Lavigne, C. (2015). The impact of landscape composition on the occurrence of a canopy dwelling spider depends on orchard management. Agriculture, Ecosystems & Environment 215(1), 20-29. DOI

• Impact des pratiques agricoles et du contexte paysager sur les dégâts provoqués par les taupins dans les cultures de maïs en France

Crop-damaging wireworms - the soil-dwelling larvae of click beetles - have resurged in Europe over the past 15 years, particularly in French maize crops. There is currently no curative treatment available to control wireworms, and preventive treatments are mainly chemical. We therefore need to better understand factors that rule damage for developing agroecological control strategies. In this investigation we tested the effect of agricultural practices and local landscape on wireworm damage in maize crops. We surveyed wireworm damage in 341 fields under various conditions in western France in 2011 and 2012. We used in particular a random forest algorithm to impute missing values, and an automated model selection routine to select the best beta regression model. Our results show that the occurrence of grassland in the rotation increases wireworm damage. Tillage also shows a high influence, though varying with season and year. Wireworm damage is decreased by the presence of hedges or cultivated crops at the field border, whereas it is increased by the presence of grassland at the field border. Overall, our findings provide some insights to develop preventive solutions for the sustainable control of wireworms, as well as a framework for data processing to analyze a wide range of similar situations involving other crops and pests.

Saussure, S., Plantegenest, M., Thibord, J.B., Larroudé, P., Poggi, S. (2015). Management of wireworm damage in maize fields using new, landscape-scale strategies. Agronomy for Sustainable Development 35(2), 793-802. DOI

• Les pratiques agricoles affectent-elles les ennemis naturels à l'échelle du paysage?

Farming practices are rarely considered in the description of agricultural landscapes. However, the variety of cropping systems creates a particular kind of heterogeneity which can strongly affect the diversity of species living in agro-ecosystems, and consequently the ecosystem services they provide.  In this study, we investigate the effects of landscape composition and configuration of organic and  conventional farming practices on three groups of aphids’ natural enemies, compared to field habitat quality and land cover heterogeneity. A field survey was carried out in 2012 and 2013 in western  France (Brittany). Ladybirds, carabid beetles and parasitoids were sampled in 40 pairs of organic and  conventional winter wheat fields, distributed along a landscape gradient of organic farming areas. The relationships between farming practices and natural enemies were investigated with a PLS-path modeling approach, hardly ever used in ecology but presenting numerous advantages to analyze multivariate systems. Results showed that abundance and species richness of natural enemies were mainly affected by local farming practices, with a higher diversity in organic fields. To a lesser extent, landscapes also affected natural enemies, but only in relation to the length and configuration of hedgerows. Our results open up avenues for the design of agricultural landscapes since our results suggest that natural enemy diversity can be enhanced without a specific organization of organic fields. We discuss methodological issues regarding the description and the analysis of farming practices at the landscape scale. We argue that such investigations require high quality maps covering large spatial extents, and the use of statistical tools providing a good handling of complex relationships occurring in agro-ecosystems.

Puech, C., Poggi, S., Baudry, J. & Aviron, S (2015). Do farming practices affect natural enemies at the landscape scale? Landsc. Ecol. 30(1), 125-140. DOI

• La dichotomie entre les pratiques biologiques et conventionnelle a-t-elle du sens pour les ennemis naturels?

As an alternative to conventional farming, organic farming is considered a promising type of production to meet the challenges of modern agriculture. In particular, organic farming is assumed to favour the biological control of pests by their natural enemies and, therefore, is considered a possible way to reduce the use of pesticides. Effects of organic vs. conventional farming on insects natural enemies have been compared, but the results remain uncertain, probably because the diversity of crop management strategies is rarely considered. In this study, we assessed whether or not the diversity of farming practices implemented in organic and conventional farming affects natural enemies of aphids (ladybirds, carabid beetles and parasitoids) in winter wheat. Entomological surveys were carried out in 20 pairs of organic and conventional fields. We interviewed the farmers to identify variables that describe farming practices and identified the most important practices using a ranking approach based on random forests. Abundances of aphids’ natural enemies were tested in relation to different levels of description of farming practices (from organic vs. conventional farming to individual practices). We found a large diversity of farming practices, which were evenly distributed along a gradient from organic to conventional farming. Abundances of aphids’ natural enemies were greater in organic fields, but the three species groups had different responses to the diversity of farming practices. Ladybirds were influenced by tillage frequency, number of wheat varieties and pesticides, and carabid beetles by tillage frequency, whereas parasitoids were not affected by any practice. Even though the organic vs. conventional farming dichotomy was meaningful to explain aphids’ natural enemies abundances, the consideration of more detailed practices improved our understanding of their response to crop management strategies. Our results help identify the level at which agro-ecosystem actors must intervene to promote effective biological control.

Puech, C., Baudry, J., Joannon, A., Poggi, S. & Aviron, S. (2014). Organic vs. conventional farming dichotomy: Does it make sense for natural enemies? Agriculture, Ecosystems & Environment, 194, 48–57. DOI

Publications antérieures au projet

• Influence du mode de production (biologique vs conventionnel) sur les bioagresseurs du blé : effet local et effet de voisinage

Les pucerons, les adventices et quatre maladies foliaires du blé (septoriose, oïdium, rouilles brune et jaune) ont été observés afin de comparer leur abondance dans un réseau de parcelles agricoles en AB et en conventionnel, entourées ou non de parcelles AB. La septoriose et les pucerons étaient plus faibles dans les parcelles en AB que da ns les parcelles conventionnelles et les parcelles, quel que soit leur mode de conduite, contenaient moins de pucerons lorsqu'elles étaient entourées d'au moins une parcelle en AB. Les adventices étaient plus nombreuses et diversifiées en AB, mais n'étaient pas influencées par la présence de parcelles en AB dans l'entourage.

Gosme, M., De Villemandy, M., Bazot, M., Jeuffroy, M.-H. (2012). Local and neighbourhood effects of organic and conventional wheat management on aphids, weeds, and foliar diseases. Agriculture, Ecosystems, Environment 161, 121–129. DOI

• Effets de la complexité du paysage et des pratiques culturales à plusieurs échelles spatiales sur le taux de parasitisme des méligèthes du colza.

Rusch, A., Valantin-Morison, M., Sarthou, J.-P., Roger-Estrade, J. (2011). Multi-scale effects of landscape complexity and crop management on pollen beetle parasitism rate. Landsc. Ecol. 26, 473–486. DOI