Bumblebee resource dynamics : a review of foraging and nesting in the agricultural landscape

Abstract: 90 % of all plants on earth either benefits or entirely depends on pollination. There are pollinators among families of bees (Apidea), butterflies (Lepidoptera) and birds (Aves). Bees of genus Bombus spp., bumblebees, are especially important and provide pollination service for 80 % of the crops of Europe and many wild plant species. The bumblebee community both rise and fall within the same year with few exceptions. Only the newborn queen survives to the next year to form a new community. Since the intensification of agriculture many bumblebees species have been declining in numbers. The purpose of this thesis was to review the drivers of bumblebees in the agricultural landscape, focusing on nesting and foraging. The aim was to understand what controls the quantity of bumblebees, which species were to be found and why them. This thesis consists of two parts: one reviewing foraging and nesting by a literature review and the other a field study of the effects of flower strips and honeybees. In the field study, I searched for bumblebee queens emerging in spring the year after an experiment with honeybees (Apis mellifera) and flower strips in fava beans (Vicia faba). I could not find a significant effect of flower strips nor honeybees in my field study. However, in my review several researches have come to the conclusion that both honeybees and flower strips can affect bumblebee density and thereby also potentially bumblebee dynamics. For instance, the impact of honeybees could be minimized by keeping the hives within the ecosystem the year around and not within areas with sensitive or endangered plant or bee species. Flower strips could potentially positively affect bumblebee population dynamics if the timing and floral quality meets the temporal need of the bumblebee populations, especially during critical events such as nest establishment and queen reproduction. We need further testing of the impact of floral abundance in the agricultural landscape and presence of honeybees on bumblebee population dynamics, mainly during critical events such as nest establishment. Because this field study was first of its kind in Sweden, the method needs to be refined to better handle the impact of timing and changes in weather. Therefore several more studies during nest establishment are needed, studying the impact of overwintering survival and fitness of queens.