The apiarian and agricultural sectors got together to set up an apiary survey in Eure-et-Loir, in 2010, during oilseed rape flowering. The aim of this observatory was to highlight what can occur during oilseed rape flowering regarding bee population evolution and agricultural practices. The year 2010 was marked by important larvae and brood mortalities which induced a national investigation. Among the 4 surveyed apiaries, 2 were also concerned by these mortalities but this could not be explained by the observations and the analysis that were carried out. However, this survey enabled us to identify apiarian and agricultural practices around the apiaries and to combine expert testimonies of apiarian and agricultural professionals.