Influence of floral diversity on ecological networks linking insect pests, their natural enemies and ants in apple orchards

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INRAE presentation

The French National Research Institute for Agriculture, Food, and Environment (INRAE) is a major player in research and innovation. It is a community of 12,000 people with 272 research, experimental research, and support units located in 18 regional centres throughout France. Internationally, INRAE is among the top research organisations in the agricultural and food sciences, plant and animal sciences, as well as in ecology and environmental science. It is the world’s leading research organisation specialising in agriculture, food and the environment. INRAE’s goal is to be a key player in the transitions necessary to address major global challenges. Faced with a growing world population, climate change, resource scarcity, and declining biodiversity, the Institute has a major role to play in building solutions and supporting the necessary acceleration of agricultural, food and environmental transitions.

Work environment, missions and activities

• 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 thesis:

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).

You will be in charge of:

- Setting up and monitoring fieldwork in Rennes orchards, as well as capturing live predators at various sites (teamwork)

- Analysis of monitoring data and molecular data on predator consumption

- Biocontrol modelling

- Co-supervision of trainees

- Broadcasting results (publications and conference presentations)

- Participating in the scientific and organisational life of the EGI team

The PhD student will be based at UMR IGEPP in Rennes (https://igepp.rennes.hub.inrae.fr/equipes-de-recherche/egi-ecologie-et-genetique-des-insectes). The thesis will be supervised by Manuel Plantegenest (PR Institut Agro Rennes, 50%), Elsa Canard (CR INRAE Rennes, 30%), and Pierre Franck (CR INRAE Avignon, 20%). Technical support will be available locally and at the other project sites for the various tasks involved in the thesis. He/she 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.

•  Scientific environment:

The Institut de Génétique Environnement et Protection des Plantes - IGEPP (Institute of Plant Genetics, Environment and Protection) is a joint research unit (UMR) responding to major societal challenges in agronomy, for agriculture that is more economical in the use of fertilisers and pesticides, and that preserves and uses biodiversity. The IGEPP brings together experts with complementary theoretical and applied skills from INRAE, the Rennes-Angers Agro Institute and the University of Rennes 1, and trains young people for a range of careers in research and higher education. Located in the west of France, 2 hours from Paris, in the heart of one of Europe's largest agricultural regions, IGEPP is spread over five geographical locations.

Training and skills

• Recommended training: Master's degree in ecology with an interest in agriculture and entomology
• Knowledge required:

- Community and interaction ecology

- Diversity sciences

- Good English level

• Appreciated experience:

- Data analysis

- Modelling Programming and/or bioinformatics

- Genetics

• Skills sought:

- Enjoys working in a team, but is able to work independently

- Good written and verbal communication skills

INRAE's life quality

By joining our teams, you benefit from (depending on the type of contract and its duration):

- up to 30 days of annual leave + 15 days "Reduction of Working Time" (for a full time);
- parenting support: CESU childcare, leisure services;
- skills development systems: training, career advise;
- social support: advice and listening, social assistance and loans;
- holiday and leisure services: holiday vouchers, accommodation at preferential rates;
- sports and cultural activities;
- collective catering.

How to apply

Send a cover letter and CV, including the contact details of 2 referees, to the 3 thesis co-supervisors: 

Elsa Canard / Manuel Plantegenest / Pierre Franck

•  By e-mail:  elsa.canard@inrae.fr

manuel.plantegenest@agrocampus-ouest.fr

Pierre.Franck@inrae.fr