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Structure, strength and invasibility of aphid food webs

Final Report Summary - APHIWEB (Structure, strength and invasibility of aphid food webs)

The project aimed at addressing changes in food web structure resulting from emigration-invasion of some of the representative of lower trophic levels (herbivores) and of their natural enemies, from their origin place to invaded regions. Migration of a given herbivore species could release it from predation pressure as stated in the enemy release hypothesis. For agricultural pests, such enemy release could result in major pest outbreaks. Conversely, increased natural enemy pressure could occur if pest enemies are ‘freed’ from the restraints imposed by upper trophic levels after migration, e.g. fewer or no hyperparasitoids. The work aimed shedding light on the resilience and/or disruption of trophic interactions within a multi-level food web after migration (of pest) or importation events (release of natural enemies in framework of classical biocontrol programs). The project has focused on invasive aphid pests, their associated natural enemies (mainly parasitoids and predators in a lesser extent) and the consumers of the latter (such as hyperparasitoids) in 6 plant systems distributed worldwide: oilseed rape, wheat, Citrus trees, soybean, Tansy plant and the complex Nerium oleander/Asclepias plants. Aphids are worldwide known pests of major importance for multiple crops. However, the pest status of the aphids on the considered crops differs across the world: they are major pests in invaded regions but often minor pests in their native region. This could account for the lower number of natural enemy species and the simpler food webs observed in native areas and thus explain the higher impact of those pests in invaded areas. In this context, we characterized food webs including natural enemies of pest aphids, e.g. parasitoids and hyperparasitoids associated with aphids in their native regions, and compared them to remote sites where these agricultural or natural ecosystems and their aphid pests also occur. For each ecosystem, sites included the native area of the plant/crop and of aphid pest(s) and included region(s) across the world that have been invaded by the aphid(s) (and where natural enemies were or were not released). The partners have been chosen in a strategic way across all continents (except Africa) to target native vs. invaded areas for each crop considered. In addition to works carried out on food webs, the project has also focused on key factors structuring trophic networks associated with aphid pests notably the factors affecting aphid parasitoid specialization (the major natural enemies of aphids worldwide) as well as other natural enemies of aphids such as predators. The work was thus divided in four main activities: (1) collection and characterization of aphids, natural enemies and intraguild consumers in crops and areas considered, (2) identification of trophic links among these arthropods for each crop, (3) building of food webs to compare them between native and invaded areas, and (4) investigate factors, notably parasitoid specialization degree, affecting success rates of introduction and/or invasion by aphid-associated natural enemies and potential biocontrol service provided. The project development followed the main indications of EU and a large part of its activities has been devoted in training young researchers, and sharing and transferring information (seminars, work meetings, international talks, course e.g. MATI in UIAUS, and publications). The aims of the project have been achieved through a dense program of secondments from and to Europe partners, of young and experienced researchers. Particularly intense has been the collaboration with Chinese and Chilean partners regarding both incoming and outgoing secondments and United States regarding outgoing secondments from Europe. Many of the partners have been involved in long duration secondments with positive effects in terms of training and milestones achieved. Overall, they can be divided into 3 categories: 1) Production of new knowledge, 2) Training, and 3) sharing information.
1) Production of new knowledge: A list of published papers (in referred international journals) as well as papers submitted or in preparation relative to the activities of the project is attached to this report. It is worthy to point out that beyond knowledge acquired on food webs in general (Senft et al. 2017; Yang et al. 2017; Zheng et al. 2016), and methods (Staudacher et al. 2016; Ye et al. 2017), papers have been produced on potential optimization of agricultural practices for optimized pest management through biological control service (Damien et al. 2017; Djoudi et al. 2018, Ortiz-Martinez & Lavandero 2018). Key documents have been also produced on factors affecting and/or potentially modulating parasitoid specialization degree (and thus on trade-off between efficiency in biocontrol and safety for non-target species) and are submitted or in preparation (Benelli et al. 2017; Desneux et al. 2018; Raymond et al. 2017; Tena et al. 2016; 2018). A large extended network of institutions working and producing outstanding knowledge on food webs and aphid natural enemies has been created owing to the APHIWEB. Multiple members of the project have been involved in the submission of a RISE project in 2017, and this activity will be renewed in the upcoming European RISE call for running projects aiming to expand research and building from the knowledge generated by the APHIWEB project. Finally, new bi- or tri-partite collaborations generated through the APHIWEB project (e.g. UIAUS-CAAS-INRA, UR1-UMN-UTAL, UTAL-UNICT-UMN, etc.) will result in multiple new joint works in the future thanks to the APHIWEB project.
2) Training: Training activity has been considered important for the success of the project and has been concentrated on various countries in need of learning standardized high end methods for collection of materials and analytical tools for food webs analyses, as well as key information related to biological control and pest management methods. Knowledge has been transferred from Europe to other partners as well as from non-European countries to European partners, this making transfer of knowledge successfully balanced overall during the course of the project. Training activities consisted in courses, co-supervision (EU-non EU) of ESRs, in seminars and applied talks to target a wide audience (see list of talks), as well as in assisting trained staffs in laboratories and fields. This has been done as much as possible, through bilateral secondments that were particularly important for showing the updated tools of EU laboratories.
3) Sharing information: One symposium has been organized at the biggest international meeting dealing with arthropods, the International Conference in Entomology (ICE2016), which was held late 2016 in Orlando; more than four thousand persons attended the conference, including many ERs and ESRs involved in APHIWEB, thus ensuring a wide dissemination of APHIWEB activities and information. Multiple talks and seminars in universities, research centers and experimental stations have been done, this enabling dissemination to both scientists and extension specialists. In addition, knowledge generated both in applied and basic topics, promoted the spill-over of key information to be applied in other agricultural systems also studied by the various APHIWEB partners e.g. cotton, with obvious wider impact of the project than actually initially planned. Finally, more than 20 papers have been published during the project and 36 more have been submitted or in preparation (some secondments ended just close to the end of the project and data are being processed). Some of these papers have already collected numerous citations which is a benchmark of the general interest on them.