Floral resource subsidies for the enhancement of the biological control of aphids in oilseed rape crops

Food production is achieved by the interaction of man-made infrastructures with natural ecosystems, the latter providing soil, light, and regulating services, including biological control. However, such natural capital has been put increasingly at risk by modern agricultural practices. For example, the use of insecticide compounds can be harmful to organisms in the soil, the water and the vegetation, including beneficial insects. This thesis investigated how the ecological management of a conventional oilseed rape (OSR) cropping system can enhance the biological control of insect pests by their natural enemies, which could alleviate the use of insecticides. OSR hosts three aphid species, namely, Brevicoryne brassicae (L.), Myzus persicae (Sulzer), and Lipaphis erysimi (Kaltenbach). In New Zealand, these three species are attacked by the parasitic wasp Diaeretiella rapae (McIntosh) [Hymenoptera: Braconidae], which completes its larval development inside an aphid body, and is a free-living organism when adult. In that stage, the wasp only feeds on carbohydrate-rich fluids, e.g. floral nectars and honeydew. Floral resource subsidies consist in the addition of nectar-providing vegetation in the habitat of parasitoids, to enhance their reproductive output, which in turn cascades into decreased pest density. This approach has known successes and failures, and its potential could be increased by a better understanding of its ecological functioning. In the introduction, this thesis lists current knowledge gaps in the ecology of floral subsidies targeted at enhancing the control of pests by parasitoids. In the second chapter, this thesis reports how nectar feeding affects the behaviour of D. rapae. It was observed that feeding on buckwheat (Fagopyrum esculentum Moench) enhanced ca. 40-fold the time spent searching for hosts and greatly reduced the time spent stationary. The consequences of this for the reproduction of the parasitoid, and biocontrol, are discussed. The third chapter addresses the potential competition between pollinators and parasitoids for nectar, when the latter is provided as a floral subsidies. This question is crucial because the potential effect of floral subsidies on biocontrol could be negated by if the provided nectar is consumed by pollinators. A manipulative field experiment indicated that this negative interaction is not existent or weak, although the power of the test was low. A laboratory trial presented in the fourth chapter showed that the longevity of D. rapae fed on OSR or buckwheat nectar was enhanced ca. 3-fold compared to unfed conspecifics. Feeding on M. persicae honeydew and nectar from two candidate floral subsidies enhanced longevity ca. 2-fold, indicating a lower nutritional quality. Two other plants did not cause any longevity enhancement. The value of these results with regard to the understanding of the nutritional ecology of D. rapae is discussed. The food-web of aphids, parasitoids and hyperparasitoids (fourth trophic level) living in OSR crops in New Zealand has not been documented. Understanding the composition and structure of the food-web is important to guide the implementation of floral subsidies. The fifth chapter presents a protocol for the reconstruction of food-webs, based on the molecular analysis of aphid mummies. The further use of this tool for the construction of aphid-based food-webs in general is discussed. The thesis findings are discussed in the context of OSR as an ephemeral, multi-species, spatially complex and dynamic habitat. The concept of “foodscape” is adapted to parasitoids and biological control. In its last section, the discussion integrates ecological and agricultural considerations to suggest the intercropping of a flowering plant in OSR crops

Effects of landscape heterogeneity on crop colonization by natural predators of pests in protected horticultural cropping systems

In Mediterranean regions, colonization of protected horticultural crops by native predatory mirid bugs is frequent, but these processes remain highly heterogeneous among crops. Our study aimed at assessing the effects of crop management practices and local landscape heterogeneity (landscape composition and configuration within 300m buffers around crops) on populations of Macrolophus and Dicyphus mirids in protected tomato crops in southern France. We found significant effects of landscape heterogeneity on mirid populations, but effects were similar for landscape composition and configuration. Tomato crops were colonized the most by Macrolophus mirids in landscapes with fallow, that seemed to act as source of mirids for crops. In contrast, crop colonization was reduced by nearby orchard, which reflected either sink or dilution effects. Mirid popuations were also reduced in crops with intensive management practices. Maintaining large areas of fallow is important to enhance native beneficial fauna, but adopting integrated plant management practices remains the most promising strategy to enhance mirid populations in protected horticultural crops

Hétérogénéité de la colonisation des cultures maraîchères sous abri par les auxiliaires indigènes : rôle de la conduite des cultures et de leur environnement paysager

La régulation des ravageurs par leurs ennemis naturels est une stratégie alternative de protection des cultures dans les systèmes maraîchers biologiques. En région méditerranéenne, les punaises mirides indigènes (Heteroptera: Miridae) colonisent spontanément les cultures sous abri, et peuvent jouer un rôle important pour le contrôle des ravageurs. Ce processus de régulation reste cependant très hétérogène d'une parcelle à une autre et peu fiable. Cette étude est réalisée dans le cadre du projet REGABRI, dont l'objectif est d'identifier les facteurs de la colonisation des cultures de tomate en agricultures biologique et conventionnelle par les mirides dans le Roussillon. Un premier suivi en 2010-2011 sur 34 cultures de tomates a montré que les abondances de mirides au sein des abris varient selon la conduite des cultures, et les caractéristiques du paysage environnant (100m à 200m). Un deuxième suivi en 2012 a permis d'identifier des éléments non cultivés et cultivés dans l'environnement des abris, susceptibles de favoriser (habitats sources) ou de réduire (effets dilution et puits) la colonisation des cultures par les mirides. Ces résultats montrent qu'une approche systémique, considérant les échelles de la parcelle, du système de culture et du paysage, est nécessaire pour optimiser la régulation naturelle des ravageurs en maraîchage sous abri.Enhancing insect pest control by their natural enemies is considered as a promising crop protection strategy in organic vegetable production systems. In Mediterranean areas, native natural enemies such as mirid bugs (Heteroptera: Miridae) settle spontaneously in protected vegetable crops and can play an important rolefor pest regulation, which remains however very heterogeneous from field to field and hardly predictable. The present study is part of the project REGABRI, which aims at identifying key factors of colonization of organic and conventional protected tomato crops by mirid bugs in Roussillon area. A first survey in 2010-2011 on 34 crops showed that mirids abundances in crops vary according to management practices and landscape features in the crops surroundings (100m to 200m). A second survey in 2012 made it possible to identify uncultivated or cultivated elements in the crops surroundings, that might enhance (source habitats) or on the contrary reduce (dilution and sink effects) tomato crops colonization by mirids. These results showed that a systemic approach, considering the field, the cropping systems as well as the landscape scale, is needed to optimize conservation biological control on protected vegetable systems

Effect of local landscape heterogeneity on crop colonization by natural predators of pests in protected horticultural cropping systems

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 (Heteroptera, Miridae) is frequent but highly heterogen eous among crop production sites. The goal of our study was to assess whether the variability in crop colonization levels by mirids (Macrolophus spp. and Dicyphus spp.) is related to local landscape heterogeneity (land - cover diversity, percent cover, and spatial configuration), and whether these effects are significantly greater or lower than those of crop management practices. We investigated relationships between mirid abundances in protected tomato crops, farming practices, and landscape metrics (calculated within 300 m buffers) in southern France (Roussillon) in 2010 and 2011. Our results show that 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 or dilution effects. Landscape composition and spatial configuration had similar effect on mirid populations. Effects of landscape heterogeneity on mirids were however lower than those of crop management practices. Our findings suggest that maintaining large areas of semi-natural habitats (fallow) is important to ensure colonization of protected crops by natural enemies of pests. Converting farms from conventional to organic production systems and adopting integrated plant management practices remain the most promising strategies to enhance populations of mirids in protected horticultural crops in Mediterranean regions

Local landscape heterogeneity affects crop colonization by natural enemies in protected horticultural cropping systems

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 100 m 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

Effects of landscape heterogeneity on crop colonization by natural predators of pests in protected horticultural cropping systems

International audienceIn Mediterranean regions, colonization of protected horticultural crops by native predatory mirid bugs is frequent, but these processes remain highly heterogeneous among crops. Our study aimed at assessing the effects of crop management practices and local landscape heterogeneity (landscape composition and configuration within 300m buffers around crops) on populations of Macrolophus and Dicyphus mirids in protected tomato crops in southern France. We found significant effects of landscape heterogeneity on mirid populations, but effects were similar for landscape composition and configuration. Tomato crops were colonized the most by Macrolophus mirids in landscapes with fallow, that seemed to act as source of mirids for crops. In contrast, crop colonization was reduced by nearby orchard, which reflected either sink or dilution effects. Mirid popuations were also reduced in crops with intensive management practices. Maintaining large areas of fallow is important to enhance native beneficial fauna, but adopting integrated plant management practices remains the most promising strategy to enhance mirid populations in protected horticultural crops

Hétérogénéité de la colonisation des cultures maraîchères sous abri par les auxiliaires indigènes : effets des modes de conduite des cultures et de leur contexte paysager

Hétérogénéité de la colonisation des cultures maraîchères sous abri par les auxiliaires indigènes : effets des modes de conduite des cultures et de leur contexte paysager. Colloque DinABio 2013 "Développement et innovation en agriculture biologique

Disentangling higher trophic level interactions in the cabbage aphid food web using high-throughput DNA sequencing

International audienceThe lack of understanding of complex food-web interactions has been a major gap in the history of biological control. In particular, a better understanding of the functioning of pest food-webs and how they vary between native and invaded geographical ranges is of prime interest for biological control research and associated integrated pest management. Technical limitations associated with the deciphering of complex food-webs can now be largely overcome by the use of high throughput DNA sequencing techniques such as Illumina MiSeq. We tested the efficiency of this next generation sequencing technology in a metabarcoding approach, to study aphid food-webs using the cabbage aphid as model. We compared the variations in structure and composition of aphid food-webs in the species’ native range (United Kingdom, UK) and in an invaded range (New Zealand, NZ). We showed that Illumina MiSeq is a well suited technology to study complex aphid food-webs from aphid mummies. We found an unexpectedly high top down pressure in the NZ cabbage aphid food-web, which coupled to a large ratio of consumer species / prey species and a lack of potential inter-specific competition between primary parasitoids, could cause the NZ food-web to be more vulnerable than the UK one. This study also reports for the first time the occurrence of a new hyperparasitoid species in NZ, as well as new associations between hyperparasitoids parasitoids and the cabbage aphid in this country. We conclude that the complexity of aphid food-webs in agricultural systems could often be underestimated, particularly at higher trophic levels; and that the use of high throughput DNA sequencing tools, could largely help to overcome this impediment

Toward an Integrated Ecology and Economics of Land Degradation and Restoration: Methods, Data, and Models

This report assesses existing data, models, and knowledge methods and recommends a way forward for the ELD Initiative. It draws from existing research, publications, and case studies to summarize current practices and identify knowledge gaps. This report begins with a review of the methods to value land-use and management options. It emphasizes the overall development goal of sustainable human well-being, not merely growth of the market economy. To obtain sustainable well-being through improved land management depends on the interaction of four basic types of capital assets: built, human, social, and natural. For example, the value of ecosystem services is the relative contribution of natural capital in combination with the other three types of assets to produce sustainable well-being. Although this report focuses on natural capital and ecosystem services, it recognizes that the understanding, modelling, and valuing of ecosystem services requires an integrated, transdisciplinary approach which includes all four types of capital and their complex interactions. Another central part of this report is a review of computer models that could be useful for analyzing and valuing land management options. This includes farm and site scale models, watershed and regional scale models, climate change models, integrated global models, and ecosystem services models. A major conclusion of this report is that truly integrated models (i.e., models that include all four types of capital and their interactions at multiple scales) are required to meet the goals of the Initiative. Examples of these types of models do exist, but further development is necessary to make them accessible to stakeholders and used in decision-making. For further development and integration of the models themselves, a more participatory approach to model development is recommended along with the possibility of adding advanced gaming interfaces to the models to allow them to be "played" by a large number of interested parties and their trade-off decisions (and the valuations they imply) to be accumulated and compared. This report concludes with a vision of what these integrated assessment and valuation tools might look like and how they would help solve the problems of land degradation, restoration, and sustainable management.This report was commisioned by Economics of Land Degradation (ELD) Initiativ

A review of methods, data, and models to assess changes in the value of ecosystem services from land degradation and restoration

This review assesses existing data, models, and other knowledge-based methods for valuing the effects of sustainable land management including the cost of land degradation on a global scale. The overall development goal of sustainable human well-being should be to obtain social, ecologic, and economic viability, not merely growth of the market economy. Therefore new and more integrated methods to value sustainable development are needed. There is a huge amount of data and methods currently available to model and analyze land management practices. However, it is scattered and requires consolidation and reformatting to be useful. In this review we collected and evaluated databases and computer models that could be useful for analyzing and valuing land management options for sustaining natural capital and maximizing ecosystem services. The current methods and models are not well equipped to handle large scale transdisciplinary analyses and a major conclusion of this synthesis paper is that there is a need for further development of the integrated approaches, which considers all four types of capital (human, built, natural, and social), and their interaction at spatially explicit, multiple scales. This should be facilitated by adapting existing models and make them and their outcomes more accessible to stakeholders. Other shortcomings and caveats of models should be addressed by adding the ‘human factor’, for instance, in participatory decision-making and scenario testing. For integration of the models themselves, a more participatory approach to model development is also recommended, along with the possibility of adding advanced gaming interfaces to the models to allow them to be “played” by a large number of interested parties and their trade-off decisions to be accumulated and compared.© 2015 Publishe