Increased density of honeybee colonies affects foraging bumblebees Kerstin Walther-Hellwig, Gerriet Fokul, Robert Frankl, Ralph Büchler, Klemens Ekschmitt and Volkmar WoltersApidologie, 37 5 (2006) 517-532DOI: https://doi.org/10.1051/apido:2006035