Hazards of pesticides to bees : 11th International Symposium of the ICP-BR Bee Protection Group ; Wageningen, (The Netherlands), November 2 - 4, 2011 / [International Commission for Plant-Bee Relationships, Bee Protection Group]. Pieter A. Oomen ... (eds.); Julius Kühn-Institut, Bundesforschungsinstitut für Kulturpflanzen