Figure 4.

Exposure of bumblebee colonies to field-relevant levels of imidacloprid decreases colony performance. Bumblebee colonies of similar mass were provided with sugar syrup (UT, n = 12), containing chlorpyrifos (CP, 150 nM, n = 6), imidacloprid (IMD, 10 nM, n = 6), or both (IMD + CP, n = 12). No pollen was provided, and bees were free to forage in a wilderness/grassland area in the west of Scotland. After 43–48 d in the field, colony performance indicators were monitored. Nests within each box are depicted with the same symbol. A) Percentage colony mass increase for each nest. B) Total number of live bees remaining in each nest. C) Number of viable brood cells on the outer face of each nest. D) Size distribution scatter of individual bee masses within each treatment group. Median values are shown by red lines. E) To report on the condition of the nests, a representative image of each nest was collected. A representative example from each treatment group is illustrated (all images are available in Supplemental Fig. S2).