Total adult worker mass of imidacloprid-supplemented and unsupplemented colonies during pre-treatment, post-treatment, and mid-winter evaluations.

The adult population sizes of colonies supplemented with 0, 20, or 100 ppb imidacloprid sugar syrup during the treatment phase were estimated by mass at the pre-treatment (August), post-treatment (October), and mid-winter (December) evaluation time points. Error bars are S.E. (colonies n = 16 (0 ppb), n = 15 (20 ppb), or n = 4 (100 ppb, first to last time point)). For a given time point, treatment groups with different letters are significantly different by DSCF (colony ranks).