Widespread contamination of wildflower and bee-collected pollen

15 There is considerable and ongoing debate as to the harm inflicted on bees by exposure to 16 agricultural pesticides. In part, the lack of consensus reflects a shortage of information on field17 realistic levels of exposure. Here, we quantify concentrations of neonicotinoid insecticides and 18 fungicides in the pollen of oilseed rape, and in pollen of wildflowers growing near arable fields. We 19 then compare this to concentrations of these pesticides found in pollen collected by honey bees and 20 in pollen and adult bees sampled from bumblebee colonies placed on arable farms. We also 21 compared this with levels found in bumblebee colonies placed in urban areas. Pollen of oilseed rape 22 was heavily contaminated with a broad range of pesticides, as was the pollen of wildflowers growing 23 nearby. Consequently, pollen collected by both bee species also contained a wide range of 24 pesticides, notably including the fungicides carbendazim, boscalid, flusilazole, metconazole, 25 tebuconazole and trifloxystrobin and the neonicotinoids thiamethoxam, thiacloprid and 26 imidacloprid. In bumblebees, fungicides carbendazim, boscalid, tebuconazole, flusilazole and 27 metconazole were present at concentrations up to 73 nanogram/gram (ng/g). Pesticide 28 concentrations in pollen collected by honeybees tended to be lower than those in pollen collected 29 by bumblebees. It is notable that pollen collected by bumblebees in rural areas contained high levels 30 of the neonicotinoids thiamethoxam (mean 18 ng/g) and thiacloprid (mean 2.9 ng/g), along with a 31 range of fungicides, some of which are known to act synergistically with neonicotinoids. Pesticide 32 exposure of bumblebee colonies in urban areas was much lower than in rural areas. Understanding 33 the effects of simultaneous exposure of bees to complex mixtures of pesticides remains a major 34 challenge. 35