Raymond Lucie

Thesis defended in december 6^th 2013
Direction: Manuel Plantegenest & Aude Vialatte

Abstract:

Frequent disturbances in agricultural landscapes cause recurring colonization events of cropland by pests and beneficial insects. The main objective of this work was to understand the ecological processes underlying field colonization and biological control by aphidophagous hoverflies which are important ecosystem service providers. Two different scales were considered for this purpose: (i) continental scale for identifying population-management units by looking for breaks in gene flow and by studying migration, and (ii) agro-ecosystem scale for identifying relevant habitat management measures by studying the population dynamics in the landscape. The results showed a lack genetic differentiation at European scale between individuals from different origins and between migrant and non-migrant individuals. This high level of genetic mixing leads to high genetic diversity which probably supports strong adaptive capacities in aphidophagous hoverfly populations in Europe. The study of population dynamics at local scale highlighted the key role of the individuals overwintering without migrating for the biological control of aphids. Biological control service provided in the fall by aphidophagous hoverflies overwintering in cropland was characterized for the first time. We also showed that semi-natural features of the landscape had a positive influence on the abundance of aphidophagous hoverflies, and that this influence varied during the year, in relation to the ecological cycle of hoverflies. This work provides valuable insights on the ecology of aphidophagous hoverflies and on the relative contribution of the diverse overwintering strategies for the biological control of aphids. It gives important information for designing landscape management measures in order to promote ecosystem services provided by hoverflies.