Title of the dissertation: Advancement in the study of cuckoo-wasps (Hymenoptera, Chrysididae)

Promoteur de thèse: Monsieur Denis MICHEZ

Summary of the dissertation: The Chrysididae are brightly coloured Hymenoptera known as « jewel wasps » or « ruby-tailed wasps » but also as “cuckoo-wasps” for their parasitoid or cleptoparasitic behaviour. The family Chrysididae includes more than 3,000 described species in 118 genera distributed all over the World, including fossils records. This family is well-known for being a taxonomically challenging group and probably for this reason cuckoo wasps have not been particularly popular among entomologists, thus suffering the taxonomic impediment, while ecology and biology are less studied than in other hymenopteran groups.The goals of the present thesis were to (i) revise the taxonomy and nomenclature of the family, both for existing and fossil taxa, for the Palaearctic region, with a focus on European fauna (ii) ascertain faunistic survey and new biological information (including potential economic and agronomic interest) and (iii) provide an update checklist of the world fauna, including all changes published in the last 35 years, the time passed since the latest global catalogue.Taxonomic goals for Europe and the Palaearctic region were reached by reordering genus-group names and describing more than 90 new species, genera, and 10 replacement names, synonymizing 88 taxa, resurrecting 73 taxa, and designating 44 lectotypes and 2 neotypes. Moreover, I contributed by adding to the barcode library of the European chrysidids some thousands barcodes for some hundreds identified species. Taxonomic work, including description of new species, including Palearctic and non-Palearctic species, particularly when these were relevant to understanding the distribution of European genera and species groups in the Afrotropical and Oriental region. A revision on Neotropical species and genera was published to provide numerous taxonomic and nomenclatural updates within the family. During the research period I also described 2 new fossils and transferred previously misidentified fossil genera and species to different subfamilies with significant new insight in the evolution timing of the family.Faunistic surveys identified endoparasitic larvae of chrysidid wasps and described in the field a novel host association of economic and agronomic interest impacting on populations of invasive alien species; in particular, together with the colleagues of the University of Turin (Italy), we described for the first time the biology of the Palaearctic species Elampus bidens (Förster, 1853) reporting a novel association with two Cicadellid leafhoppers of major agricultural economic importance that were introduced to Europe: Scaphoideus titanus Ball, 1932 and Orientus ishidae (Matsumura, 1902), both vectors of Flavescence Dorée. Moreover, faunistic surveys were often accompanied with a better definition of the distribution of cuckoo wasps in the Palaearctic, specifically in the Levant and the Middle East and Arabian, in Mongolia and the Himalayas. These surveys played a key role in improving our understanding of the distribution of European species, particularly by revealing previously unknown southernmost ranges of European species as well as easternmost ranges. Overall, the range of these taxonomic and faunistic publications highlights how much work remains to be done, not only in the Palaearctic region, which is currently the best studied in terms of taxonomy and distribution, but especially in other zoogeographical regions that still lack fundamental taxonomic research and essential tools such as identification keys.A the end of this research, two main catalogues were produced: (1) the first illustrated catalogue of chrysidid teratologies the first also in a non-social hymenopteran family synonymizing genera and species and providing frequencies of specific malformations evaluated on more than 16,000 specimens examined; (2) the new world catalogue for the whole family, listing more than 3,200 changes for 2,138 taxa, including new entries and corrections to the previous checklist on a total of 3,030 valid species and 4,902 names.All the taxonomic and faunistic work of the last years will be useful to develop study in Conservation Biology. By developing a collection of 140,000 distributional records of chrysidids from European museums, we are now ready of the next step of biodiversity assessments, such as the IUCN Red List. Cuckoo wasps are directly affected by the decline of their host species, as they are brood parasites. Any factor that negatively impacts the habitats of their hosts also poses a threat to cuckoo wasps themselves, such as intensive agricultural and forestry practices, habitat fragmentation, and pesticides. The scares European National Red Lists for Chrysididae classify about half of all chrysidid species as threatened, comparing historical and current data, and showing dramatic population declines for many species. However, while the decline appears more evident in Nordic and Central Europe, this impression is likely the result of collection bias, as no comparable temporal or spatial data exist for Mediterranean countries. The effects of climate change on cuckoo wasps are more complex to assess, as most species are considered thermophilic. A warming climate may negatively impact certain host species due to deteriorating environmental conditions. On the other hand, rising temperatures may allow some warmth-adapted species to expand their ranges into central and northern Europe. Conservation studies represent the next future step for this research.