Abstract EN:

Subterranean termites have been known to occur in France since the 17th century. Aquitaine, one of the most infested French regions, is inhabited by the Reticulitermes grassei species, which is particularly tricky to eradicate. The company Dow Agrosciences initiated a project together with the CNRS that aimed to clarify the patterns of this species biology in order to optimise the use of the baiting system technology. In order to elucidate the historical origins of the infestation by termites in France, we first inferred the evolutionary history of R. Grassei. We demonstrated that ancestral populations survived in the south of the Iberian Peninsula during the Quaternary glaciations, before expanding towards northern areas, successively colonising central and northern Spain, and finally France. A phylogeographical study of R. Grassei populations combining ecological, behavioural, chemical and genetic approaches enabled us to identify the migration routes followed by the pioneer populations and their consequences on the present genetic structure of populations established in geographically distinct areas. We also demonstrated the phylogenetic proximity that exists between R. Grassei and R. Banyulensi, another Iberian species. The study of subterranean termite's social and colonial organisation provided new insights on their ability to adapt to urban constraints. The identification of the genetic structure of R. Grassei colonies collected across France and Spain helped to understand their spatial distribution under natural conditions and on their ability to extend through the production of secondary reproductives. R. Grassei colonies can be divided in simple and complex families, based on the number and on the genetic relatedness of the reproductives. By investigating the survival and the development of laboratory colonies, we demonstrated this species' ability to restart an new colony in few months from a few dozens of isolated workers which can differentiate into secondary neotenic reproductives. The originality of termite's life cycle, their good lifespan and their ontogenetic potentialities, unique among social insects, are all factors that serve their settlement and their persistence in human inhabited areas, even the ones that are protected with chemical treatments.