Scientific Context:
Insect pests are the target of numerous insecticide treatments that are harmful to human health and biodiversity, particularly in apple orchards. An alternative to the use of insecticides lies in the setting up of agricultural practices favorable to the regulation of pests by their natural enemies (conservation biological control). Among these practices, the diversification of plant cover is particularly promising. On the one hand, floral resources provided by spontaneous vegetation or planted flower strips can supplement the diet of natural enemies (pollen, nectar, alternative prey), but they can also divert ants from hemipteran pests (aphids, mealybugs), which maintain mutualistic relationships with them and, in exchange for honeydew, repel, disrupt or kill the natural enemies of these pests. The aim of this thesis is to describe and quantify the influence of floral resource supply on the composition of arthropod communities observed in apple orchards, and on ecological interactions between pests, natural enemies, ants and plant species. Trophic interactions will be revealed using molecular techniques to detect the DNA of animal prey and plant resources consumed by natural enemies. These analyses will provide tools for quantifying the impact of the availability of floral resources (spontaneous or implanted) for natural enemies and ants on the expected level of biological control of insect pests in apple orchards.
Description of the project:
Part 1. Impact of floral resources on the composition and abundance of predatory arthropod communities and ants in apple orchards.
The first part will focus on analyzing the community of specialist and generalist predators, as well as ant species, present in trees as a function of managed or spontaneous floristic diversity. To this end, the PhD student will mobilize data on natural predator communities in apple orchards already available in the laboratory and currently being collected as part of the Diver’ant project, including monitoring in the Rennes basin to which the PhD student will contribute. Analysis of the results will enable us to assess how the presence of floral resources influences the presence and abundance of predators and ants.
Part 2. Detailed description and analysis of ecological networks involving predators in apple orchards.
The second part will focus on the analysis of trophic relationships between predatory arthropods and insect pests and floral species using molecular detection (diagnostic PCR and barcoding). Predators (including spiders, ladybugs, forficula, hoverflies and bugs) will be sampled in orchards monitored as part of the Diver’Ant project. The predators will be captured alive and their DNA extracted in the laboratory to detect the presence of residual prey and plant DNA in their digestive tract, using two complementary approaches. Diagnostic PCRs will measure the detection frequency of a few targeted pests in apple orchards (e.g. aphids and codling moths), while barcode sequencing will allow identifying the full spectrum of prey and floral resources consumed by natural enemies. Analysis of the results will enable us to assess how the presence of ants and the availability of floral resources influence the frequency of consumption of targeted pests by specialist beneficials (eg. ladybugs) and the range of prey exploited by generalist species (eg. spiders, forficula), and more generally the structuring of ecological networks.
Part 3. Modelling biocontrol in apple orchards.
A third part will focus on modelling the effect of natural enemies on pest populations, i.e. biocontrol, and exploring how the presence of ants modulates this biocontrol. To this end, population dynamics and abundance monitoring data on pests, ants and natural enemies, as well as predation frequencies detected by molecular analysis, will be mobilized to fit a model quantifying the impact of natural enemies on pest population dynamics as a function of ant presence. This model will explore how a change in the interaction network around the pest affects the evolution of its abundance. In practice, we will assume that the rate of increase in pest populations depends on the action of natural enemies (proportional to their abundance and voracity), determined by the abundance and composition of auxiliary communities, but also by their predation intensity, modulated by the presence of ants. The influence of floral resource availability on the abundance and behavior of natural enemies and ants will also be considered as a potential lever for modulating biocontrol. The data mobilized will be data already available on the dynamics of the aphid Dysaphis plantaginea in cider orchards (Laurence Albert thesis) and from new collections in apple orchards where strategies to reduce ant abundance will be deployed (Diver’Ant project). Comparisons can be made with observations of the same type from monitoring of beneficials and pests in clementine orchards (IRIS project).
Working environnement:
The PhD student will be based at UMR IGEPP in Rennes. He will benefit from funding acquired through the EcoControl project (Astrid Cruaud, INRAE, UMR CBGP, Montpellier) and will work closely with participants in the Diver’Ant project (Bruno Jaloux, Institut Agro IGEPP, Angers; Pierre Franck, INRAE, PSH, Avignon). Visits to Avignon and Montpellier are planned. Monitoring and capture in apple orchards will be carried out in collaboration with PSH Avignon and IGEPP Angers. Operating and molecular analysis costs will be covered by the EcoControl and Diver’Ant projects.
Supervision:
PhD supervisor: Manuel Plantegenest, PR Institut Agro Rennes, 40%
Manuel.Plantegenest@agrocampus-ouest.fr
Co-supervision 1: Elsa Canard, CR INRAE Rennes, 30%
Elsa.Canard@inrae.fr
Co-supervision 2: Pierre Franck, CR INRAE Avignon, 30%
Pierre.Franck@inrae.fr
Skills requirements:
Master’s degree in ecology with an interest in agriculture and entomology. Skills in data analysis, modeling and/or bioinformatics will be appreciated.
Salary:
Statutory (2 200 euros gross per month)
Application:
Send a CV and a cover letter to the 3 supervisors(Manuel.Plantegenest@agrocampus-ouest.fr; elsa.canard@inrae.fr; pierre.franck@inrae.fr). Provide the name and contact details of one or two referees, and possibly a letter of recommendation. Application deadline: September 4.
References:
Albert, L., 2017. Régulation Naturelle du Puceron Cendré et Aménagement Agro-écologique: l’Exemple des Vergers Cidricole du Nord-Ouest de la France (phD). Agrocampus Ouest, Rennes,
Albert, L., Franck, P., Gilles, Y., Plantegenest, M., 2017. Impact of agroecological infrastructures on the dynamics of Dysaphis plantaginea Passerini (Hemiptera: Aphididae) and its natural enemies in apple orchards in northwestern France. Environemental Entomology 46, 528–537. https://doi.org/10.1093/ee/nvx054
Anjos, D.V., Tena, A., Viana-Junior, A.B., Carvalho, R.L., Torezan-Silingardi, H., Del-Claro, K., Perfecto, I., 2022. The effects of ants on pest control: a meta-analysis. Proceedings of the Royal Society B: Biological Sciences 289, 20221316. https://doi.org/10.1098/rspb.2022.1316
Etienne, L., Rusch, A., Lavigne, C., Fouillet, E., Delière, L., Franck, P., 2023. Less field-level insecticides, but not fungicides, in small perennial crop fields and landscapes with woodlands and organic farming. Agricultural Systems 204, 103553. https://doi.org/10.1016/j.agsy.2022.103553
Tibi, A., Martinet, V., Vialatte, A., Alignier, A., Angeon, V., Bedoussac, L., Bohan, D., Bougherara, D., Cordeau, S., Courtois, P., Deguine, J.-P., Enjalbert, J., Fabre, F., Fréville, H., Grateau, R., Grimonprez, B., Gross, N., Hannachi, M., Launay, M., Lelievre, V., Lemariè, S., Martel, G., Navarrete, M., Plantegenest, M., Ravigné, V., Rusch, A., Suffert, F., Thoyer, S., 2022. Protéger les cultures en augmentant la diversité végétale des espaces agricoles. Rapport scientifique de l’Expertise scientifique collective. INRAE. 86 pages. https://doi.org/10.17180/awsn-rf06
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